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Effect of cortisol on blood pressure and the renin-angiotensin system in fetal sheep during late gestation

Alison J. Forhead, Fiona Broughton Pipkin* and Abigail L. Fowden

MS 9845 Received 15 July 1999; accepted after revision 28 March 2000.

	ABSTRACT

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1. The effects of cortisol on blood pressure and the circulating components of the renin-angiotensin system (RAS) were investigated in sheep fetuses during late gestation and after exogenous cortisol infusion.

2. Plasma cortisol concentration was greater in fetuses at 140 ± 1 days of gestation (term 145 ± 2 days) compared to those studied earlier in gestation (128 ± 1 days), although, because of wide inter-animal variation, no differences were observed in blood pressure or plasma angiotensin II (AII), renin or angiotensinogen (Ao) concentrations.

3. At 129 ± 1 days of gestation, an infusion of cortisol for 5 days (2-3 mg kg^-1 day^-1 i.v.) increased plasma cortisol concentration to a value normally seen close to term. This rise in plasma cortisol was accompanied by increases in blood pressure and plasma concentrations of AII, renin and Ao.

4. When observations from all fetuses were considered, plasma cortisol concentration correlated with plasma AII and renin, and blood pressure correlated with plasma cortisol and AII concentrations.

5. Intravenous administration of an AII type 1 (AT₁)-specific receptor antagonist (3 mg kg^-1 GR138950) caused a reduction in blood pressure in all fetuses; the hypotensive response was greatest in fetuses studied near term and in the cortisol-treated fetuses. Overall, the magnitude of the hypotension induced by GR138950, and the concomitant rise in plasma renin, both correlated with the plasma cortisol concentration before GR138950 treatment.

6. These findings show that, in the sheep fetus during late gestation, the RAS becomes more important in the maintenance of resting blood pressure when plasma cortisol concentration is elevated, whether endogenously or exogenously.

	INTRODUCTION

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Glucocorticoids increase blood pressure in fetal and adult animals (Krakoff et al. 1975; Nakamoto et al. 1991; Tangalakis et al. 1992) although the mechanisms of action are poorly understood. A number of studies have suggested that activation of the renin-angiotensin system (RAS) may be partially responsible for the hypertension induced by glucocorticoids both before and after birth (Krakoff et al. 1975; Suzuki et al. 1982; Nakamoto et al. 1991; Tangalakis et al. 1992; Sato et al. 1994b). For example, in fetal sheep, the rise in blood pressure caused by a 24 h period of cortisol infusion is associated with an increase in vascular sensitivity to exogenous angiotensin II (AII; Tangalakis et al. 1992).

In all species studied so far, plasma glucocorticoid concentration in the fetus normally rises close to term (Fowden et al. 1998). In several species, this prepartum cortisol surge coincides with an ontogenic increase in fetal blood pressure (Reeves et al. 1972; Boddy et al. 1974; Macdonald et al. 1983; Forhead et al. 1998a), and is associated with a number of maturational changes in the activity of the fetal RAS. In fetal sheep, increases in renal renin mRNA and content, and plasma renin concentration are observed towards term (Broughton Pipkin et al. 1974; Carbone et al. 1993; Rawashdeh et al. 1996), and the plasma renin response to stimuli such as haemorrhage, hypoxaemia and nitroprusside-induced hypotension is greater in fetuses near term compared to those studied earlier in gestation (Robillard et al. 1981, 1982; Rawashdeh et al. 1988). Furthermore, in many species, there are ontogenic and tissue-specific changes in the expression of the two major AII receptor subtypes, AT₁ and AT₂, over the perinatal period (Robillard et al. 1995; Shanmugam & Sandberg, 1996). Moreover, the ability of the sheep fetus to maintain normal blood pressure during haemorrhage improves near term but only in fetuses with an intact RAS (Robillard et al. 1982; Gomez & Robillard, 1984).

These findings suggest that the fetal RAS becomes more important in cardiovascular control with increasing gestational age and that developmental changes in its activity may contribute to the ontogenic rise in blood pressure seen in the fetus towards term. However, the extent to which maturation of the fetal RAS and cardiovascular function depend upon the prepartum cortisol surge is unclear. Therefore, the present study investigated the effects of endogenous and exogenous rises in plasma cortisol on basal blood pressure and the circulating components of the RAS, and on the blood pressure response to AT₁-specific receptor antagonism, in fetal sheep during late gestation. Changes in the activity of the fetal RAS after AT₁-specific receptor blockade were also examined.

	METHODS

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Animals

Twenty-nine Welsh Mountain sheep fetuses of known gestational age were used in this study. Twenty were twins and nine were single fetuses. All the ewes were kept in pens individually and maintained on 200 g day^-1 concentrates with free access to hay, water and a salt-lick block. Food, but not water, was withheld for 18-24 h before surgery, which occurred between 115 and 133 days of gestation (term 145 ± 2 days). All surgical and experimental procedures were carried out in accordance with the UK Animals (Scientific Procedures) Act 1986.

Surgical procedures

Under halothane anaesthesia (1·5 % in O₂-N₂O) with positive pressure ventilation, an intravascular catheter was inserted into the maternal femoral artery. In all of the fetuses, the femoral artery and two branches of the femoral vein were catheterised as described previously (Comline & Silver, 1972). In brief, a mid-line incision was made in the abdominal wall of the ewe in dorsal recumbency. The hindlimb of the fetus was exposed through an incision in the uterine wall and the catheters were inserted such that the tips were placed in the inferior vena cava and dorsal aorta. An additional catheter was sutured to the fetal hindlimb to monitor amniotic fluid pressure. All catheters were exteriorised through the flank of the ewe and secured in a plastic pouch sutured to the skin. From the day after surgery, the catheters were flushed daily with heparinised saline solution (100 i.u. ml^-1 heparin in 0·9 % w/v saline). Antibiotic (procaine penicillin: Depocillin, Mycofarm, Cambridge, UK) was administered I.M. to all ewes on the day of surgery and for 3 days thereafter. The fetuses were injected I.V. with 100 mg ampicillin (Penbritin, Beecham Animal Health, Brentford, UK) and 2 mg gentamicin (Frangen-100, Biovet Ltd, Mullingar, Ireland) at surgery. Experiments were carried out at least 4 days after surgery.

Experimental protocol

The fetuses were randomly divided into one of three treatment groups. On the day of study, they were all administered a bolus injection of an AT₁-specific receptor antagonist 1-((3-bromo-2-(2(((trifluromethyl)sulphonyl)amino)-phenyl)-5-benzofuranyl)methyl)4-cyclopropyl-2-ethyl-1H-imidazole-5-carboxamide (GR138950; Glaxo-Wellcome Research and Development Ltd, Ware, UK) I.V. at a dose of 3 mg kg^-1. Twenty-three fetuses were studied on either 128 ± 1 days (n = 11) or 140 ± 1 days (n = 12) of gestation. Seven of the fetuses at 128 days were given GR138950 on the fifth day of a continuous infusion of saline (0·9 % sodium chloride I.V.) and the remainder were untreated before GR138950 administration. A third group of six fetuses aged 129 ± 1 days were administered GR138950 on the fifth day of a continuous infusion of cortisol (2-3 mg kg^-1 day^-1 in 0·9 % sodium chloride I.V.; Efcortelan, Glaxo-Wellcome Ltd, Ware, UK). The dose of exogenous cortisol infused was calculated to achieve plasma cortisol concentrations similar to those normally seen close to term, i.e. similar to those determined in the fetuses at 140 days of gestation on the day of the study. Solutions of cortisol and saline were infused at a rate of 2·5 ml day^-1.

In the fetuses infused with either cortisol or saline, maternal and fetal arterial blood pressures, and amniotic fluid pressure were measured for at least 2 h before the infusion began. Mean fetal and maternal basal blood pressures were calculated from five measurements made at 10 min intervals. An arterial blood sample (10-12 ml) was taken from the ewe and fetus at the end of the recording period, and smaller blood samples (2 ml) were taken daily thereafter for the duration of the infusion. In all animals on the day of GR138950 administration, maternal and fetal blood pressures, and amniotic fluid pressure were monitored continuously from 0·5 h before to at least 2 h after drug treatment. Blood pressure measurements were made at -30, 0, 15 and 30 min, and 1 and 2 h. The mean value of blood pressure taken before GR138950 administration was used as the basal blood pressure measurement. Blood samples were taken from the ewe and fetus at 0 h (10-12 ml) and at 2 h (2 ml) after the administration of GR138950.

Exogenous AII pressor response tests were carried out in all of the fetuses in order to determine the efficacy of blockade of RAS activity using GR138950. Bolus injections of AII (100 ng (kg estimated fetal body weight)^-1 in 0·9 % saline I.V.; Hypertensin, Ciba-Geigy Pharmaceuticals, Horsham, UK) were given to the fetuses at 0, 0·5, 1 and 2 h after GR138950 administration. There were no significant differences in the pressor responses to exogenous AII between the three treatment groups at any time point. Before GR138950 administration, the mean change in blood pressure in response to AII was 10 ± 1 mmHg (n = 29). In all fetuses, GR138950 abolished the pressor response to AII at all time points examined.

At the end of the experimental period, all ewes and fetuses were killed by maternal administration of a lethal dose of barbiturate (200 mg kg^-1 sodium pentobarbitone I.V.).

Physiological and biochemical analyses

Mean maternal and fetal blood pressures, and amniotic fluid pressure were monitored using pressure transducers connected to a chart recorder (Lectromed UK Ltd, Letchworth, UK). Measurements were made with the transducers placed at the level of the maternal and fetal hearts. Fetal blood pressure was expressed less amniotic fluid pressure.

Arterial blood samples were analysed for pH and gas tensions (P_a,O2 and P_a,CO2) by an ABL330 Radiometer analyser, and for O₂ saturation and haemoglobin (Hb) concentration by an OSM2 Hemoximeter (Radiometer, Copenhagen, Denmark). For the determination of plasma AII, 8 ml of blood was placed into chilled tubes containing 0·025 M o-phenanthroline and 0·125 M EDTA, centrifuged at 1000 g and 4°C for 5 min, and the plasma was immediately extracted onto cation exchange resin (Dowex AG50W-X2; Bio-Rad Laboratories, Richmond, VA, USA). The remainder of the blood was placed into EDTA-containing tubes and centrifuged at 1000 g and 4°C for 5 min. The plasma was removed and stored at -20°C to await analysis.

Plasma AII, renin and Ao concentrations were measured by radioimmunoassay as described previously (Broughton Pipkin & Smales, 1977; Craven & Symonds, 1978; Tetlow & Broughton Pipkin, 1983). The lower limits of detection were 5 pg ml^-1 for AII, 0·5 ng ml^-1 h^-1 for renin and 0·01 µg ml^-1 for Ao, and the interassay coefficients of variation were 9·9, 16·1 and 12·7 %, respectively. The antiserum against AII cross-reacted with the hexapeptide (85 %) and heptapeptide (63 %) fragments of AII (Broughton Pipkin & Smales, 1977). Plasma cortisol concentration was measured by radioimmunoassay as described previously (Robinson et al. 1983). The lower limit of detection was 1·0-1·5 ng ml^-1 and the inter-assay coefficient of variation was 11 %.

Statistical analyses

The hormonal data are presented as median values followed by lower and upper quartiles (25 %, 75 %), and the haematological data and arterial blood pressure are presented as mean values ± S.E.M. All data were assessed for normality using the Kolmogorov-Smirnov test. Data that demonstrated a normal distribution were subsequently analysed by parametric statistical tests, whereas data that did not were analysed by non-parametric methods.

No significant differences were observed between the variables measured in the untreated and saline-infused fetuses at 128 days and, therefore, these values were pooled for analysis. Significant differences in basal values between the three treatment groups were determined by either factorial ANOVA followed by Tukey's test or Kruskal-Wallis ANOVA followed by Dunn's test. Significant differences in measurements made only on days 0 and 5 in the saline and cortisol-infused fetuses, and in the values observed at 0 and 2 h after GR138950 administration in all fetuses, were determined using either Student's paired t test or Wilcoxon's signed-rank test. The effects of saline or cortisol infusion on variables with 5 days of data were analysed by two-way ANOVA using log-transformed data. Where plasma renin was zero, an arbitrary value of 0·1 was used and added to all other plasma renin values in the analysis. Subsequent effects of treatment or time were analysed by Tukey's test and ANOVA for repeated measures, respectively. Blood pressure responses to GR138950 were assessed by ANOVA for repeated measures. Relationships between the variables measured were determined by Spearman's Rank Order correlation and partial correlation analyses. The correlation analyses were performed using all observations available from all fetuses. Differences where P < 0·05 were regarded as significant.

	RESULTS

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Effect of gestational age

Fetal plasma cortisol concentration was significantly increased with increasing gestational age (Table 1). The plasma concentration of cortisol in the fetuses at 140 days was significantly greater than that observed in those at 128 days (P < 0·05, Table 1). The mean value of arterial blood pressure in the older group of fetuses was greater than that observed in the fetuses studied earlier in gestation, but this difference was not statistically significant (P > 0·05, Table 1). There were no significant differences in plasma concentrations of AII, renin and Ao between the two age groups (P > 0·05 in all cases, Table 1).

Table 1. Mean (± S.E.M.) blood pressure, and median (25%, 75 %) plasma concentrations of cortisol, AII, renin and Ao, in the three groups of fetuses before the administration of GR138950

Effect of exogenous cortisol infusion

An exogenous infusion of cortisol for 5 days significantly increased plasma concentrations of cortisol (F = 94·2, P < 0·0005, Fig. 1A and Table 2), renin (F = 11·4, P < 0·005, Fig. 1B and Table 2) and Ao (F = 24·1, P < 0·0005, Fig. 1C and Table 2) above those seen in the saline-infused fetuses. On all days of infusion, plasma cortisol concentration in the cortisol-treated fetuses was significantly greater than that observed in the saline-treated fetuses at the same gestational age (P < 0·001, Fig. 1A and Table 2), and on the fifth day of infusion was similar to the value seen in the fetuses studied close to term (Table 1). Plasma renin concentration in the cortisol-treated fetuses was significantly increased to a value above that seen in the saline-treated fetuses on days 3 and 4 of infusion (P < 0·05, Fig. 1B and Table 2). On days 2, 3, 4 and 5 of infusion, plasma Ao concentration was significantly greater in the fetuses treated with cortisol compared to those treated with saline (P < 0·05, Fig. 1C and Table 2). On the fifth day of infusion, a significant increase in plasma AII was observed in the cortisol-, but not saline-treated fetuses (P < 0·05, Table 2).

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Figure 1. Mean (± S.E.M.) log10 plasma concentrations of cortisol (A), renin (B) and Ao (C) in saline- () and cortisol-infused () fetuses during 5 days of cortisol infusion For each variable, values with different letters are significantly different (P < 0·05); significant differences between values in saline- and cortisol-infused fetuses are indicated at each time point (*P < 0·05).

Table 2. Median (25 %, 75 %) plasma concentrations of cortisol, AII, renin and Ao, and mean (±S.E.M.) blood pressure, in the saline and cortisol-treated fetuses over the period of infusion

After 5 days of exogenous cortisol infusion, blood pressure was significantly increased by 8 ± 2 mmHg (P < 0·05, Table 2). Mean arterial blood pressure in the cortisol-infused fetuses was significantly greater than that observed in untreated and saline-infused fetuses studied at the same gestational age (P < 0·05, Table 1), and resembled that seen in the fetuses near term (P > 0·05, Table 1). Saline infusion had no significant effect on blood pressure or plasma concentrations of cortisol, AII, renin and Ao (P > 0·05 in all cases, Fig. 1 and Table 2).

When all observations from the fetuses of all groups were considered, irrespective of treatment or gestational age, significant positive relationships were seen between blood pressure and plasma concentrations of both cortisol (r = 0·47, n = 42, P < 0·005) and AII (r = 0·45, n = 30, P < 0·05). Partial correlation analysis showed that the plasma concentration of cortisol in the fetus was the more important determinant of blood pressure (r = 0·59, n = 30, P < 0·05) than the circulating AII concentration (r = -0·10, n = 30, P > 0·05) or gestational age (r = 0·15, n = 30, P > 0·05). Plasma cortisol concentration was significantly correlated with plasma AII (r = 0·63, n = 30, P < 0·0005) and renin (r = 0·48, n = 94, P < 0·0005), but not Ao concentrations (r = 0·20, n = 94, P > 0·05). Overall, a significant positive relationship was also observed between circulating AII and renin concentrations (r = 0·82, n = 30, P < 0·0005).

Effect of AT₁-specific receptor blockade

In all three groups of fetuses, the AT₁-specific receptor antagonist GR138950 caused a significant decrease in blood pressure within 15 min of administration (P < 0·001 in all cases, Fig. 2). This hypotensive response was maintained for at least 2 h after drug treatment (Fig. 2). At all time points examined, the magnitude of the fall in blood pressure induced by GR138950 in the fetuses near term, whether expressed as an absolute or percentage value, was significantly greater than that seen in the fetuses studied at an earlier age (P < 0·05, Fig. 2). Overall, a significantly greater maximal reduction in blood pressure was seen within 2 h of GR138950 administration in fetuses at 140 days (-14 ± 2 mmHg, -28·9 ± 2·5 %) compared with those at 128 days (-7 ± 1 mmHg, -15·0 ± 1·4 %, P < 0·05 in both cases). Furthermore, the hypotension induced by GR138950 in the cortisol-infused fetuses (-14 ± 1 mmHg, -26·3 ± 1·6 %) was almost identical to that observed in the fetuses near term, and was significantly greater than that seen in the untreated and saline-infused fetuses studied at the same gestational age (P < 0·05, Fig. 2). When values from all fetuses were pooled, significant positive relationships were observed between the magnitude of the fall in blood pressure induced by GR138950 within 2 h of administration and pretreatment plasma concentrations of both cortisol (r = 0·68, n = 29, P < 0·0005, Fig. 3) and renin (r = 0·41, n = 29, P < 0·05).

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Figure 2. Mean (± S.E.M.) percentage change, from the pretreatment baseline, in fetal blood pressure following the administration of GR138950 in the untreated and saline-infused fetuses at 128 days (), the untreated fetuses at 140 days () and the cortisol-infused fetuses at 129 days () Baseline values are given in Table 1. In all groups, significant differences from baseline are indicated at each time point (*P < 0·05). For each individual time point, values with different letters are significantly different (P < 0·05).

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Figure 3. Relationship between basal plasma cortisol concentration and the maximal change in blood pressure induced by GR138950 within 2 h of administration Untreated () and saline-infused () fetuses at 128 days, untreated fetuses at 140 days () and cortisol-infused fetuses at 129 days (); r = 0·68, n = 29, P < 0·0005.

Within 2 h of GR138950 administration, plasma renin concentration was significantly increased in all three groups of fetuses (P < 0·005 in all cases, Fig. 4). A significantly greater rise in plasma renin was induced by GR138950 in the fetuses at 140 days compared with those at 128 days (P < 0·05, Fig. 4). Overall, a significant positive correlation was observed between the magnitude of the fall in blood pressure induced by GR138950 and the concomitant change in plasma renin concentration (r = 0·75, n = 29, P < 0·0005, Fig. 5). In addition, the change in plasma renin was significantly correlated with basal plasma concentrations of both cortisol (r = 0·50, n = 29, P < 0·005) and renin (r = 0·50, n = 29, P < 0·05). A significant decrease in plasma Ao concentration was observed within 2 h of GR138950 administration in all three groups of fetuses (P < 0·05 in all cases, Table 3). No significant difference was seen in the change in plasma Ao induced by GR138950 between the three treatment groups (P > 0·05, Table 3).

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Figure 4. Median (25 %, 75 %) values of plasma renin concentration in the three groups of fetuses before (0 h) and 2 h after the administration of GR138950 Group 1, untreated and saline-infused fetuses at 128 days; Group 2, untreated fetuses at 140 days; Group 3, cortisol-infused fetuses at 129 days. For each treatment group, significant changes are indicated at each column (*P < 0·05, **P < 0·005). Between the treatment groups, columns with different letters are significantly different (P < 0·05). The lower and upper quartiles are indicated by the dots below and above the median values.

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Figure 5. Relationship between the changes in plasma renin and blood pressure induced by GR138950 within 2 h of administration Untreated () and saline-infused () fetuses at 128 days, untreated fetuses at 140 days () and cortisol-infused fetuses at 129 days (); r = 0·65, n = 28, P < 0·0005.

Table 3. Median (25 %, 75 %) plasma Ao and mean (± S.E.M.) haematological parameters in the three groups of fetuses before (0 h) and 2 h after the administration of GR138950

In all treatment groups, GR138950 caused a significant increase in arterial P_CO2 and significant reductions in pH and O₂ saturation (P < 0·05 in all cases, Table 3). A small but significant decrease in P_a,O2 was observed in the untreated and saline-infused fetuses at 128 and 140 days (P < 0·05 in both cases, Table 3). Arterial O₂ content was reduced in all fetuses within 2 h of GR138950 administration, but this change was only significant in the two groups of fetuses at 128 days (P < 0·05 in both cases, Table 3). Haemoglobin content was significantly increased by GR138950 in the untreated and saline-infused fetuses at 128 and 140 days (P < 0·05 in both cases), but remained unchanged in the cortisol-infused fetuses (P > 0·05, Table 3).

	DISCUSSION

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The present study showed, in fetal sheep during late gestation, that the rise in blood pressure induced by an infusion of cortisol was accompanied by an enhanced hypotensive response to AT₁-specific receptor blockade. This suggests that activation of the RAS may be one mechanism by which cortisol induces hypertension in utero. Indeed, an infusion of cortisol raised circulating concentrations of AII, renin and Ao. Because of wide inter-animal variation, no significant differences in blood pressure or in the components of the RAS measured were seen in fetuses with an endogenous increase in plasma cortisol, although the hypotensive response to the AT₁-specific receptor antagonist was accentuated. Indeed, in all animals, high plasma renin concentration was associated with a greater reduction in blood pressure following GR138950 treatment. These findings suggest that the fetal RAS makes a significant contribution to the maintenance of blood pressure, and that this influence increases with gestational age and after cortisol administration.

Previous studies have indicated a role for the RAS in glucocorticoid-induced hypertension in both fetal and adult animals. Cortisol infusion for 24 h in sheep fetuses has been shown to cause a rise in blood pressure which is accompanied by an increase in vascular sensitivity to exogenous AII (Tangalakis et al. 1992). In adult rats, the hypertension induced by administration of the synthetic glucocorticoid dexamethasone is markedly attenuated in the presence of an angiotensin-converting enzyme (ACE) inhibitor (Sato et al. 1994b). In addition, the RAS appears to be more important in the maintenance of blood pressure in sheep fetuses whose growth is restricted by carunclectomy (Edwards et al. 1999). Plasma cortisol concentration is elevated in these fetuses during late gestation (Phillips et al. 1996), and the hypotensive response to captopril, an ACE inhibitor, is greater than that seen in control fetuses (Edwards et al. 1999). Adrenalectomy in utero has been shown to attenuate the ontogenic rise in blood pressure observed in sheep fetuses between 115 and 125 days of gestation (Unno et al. 1999). However, to date, the effects of adrenalectomy on fetal blood pressure and the RAS have not been investigated close to term when plasma cortisol concentration is normally high.

There are a number of possible mechanisms by which cortisol may upregulate the activity of the RAS and, consequently, influence cardiovascular control in utero. First, in the present study, cortisol increased the circulating concentration of AII. As in the adult animal, AII via peripheral and central actions is a potent vasoconstrictor in the fetus, and has been shown previously to increase fetal blood pressure (Iwamoto & Rudolph, 1981). In addition, in fetal sheep, AII increases blood pressure without causing a significant change in heart rate which may reset resting blood pressure to a higher level (Ismay et al. 1979).

The cortisol-induced increase in plasma AII may originate from activation of the factors responsible for AII production. Indeed, cortisol caused increases in plasma renin and Ao concentrations in the present study. This finding contrasts with those from previous investigations in which cortisol infusion for 48 h (3 mg h^-1 I.P.) and 5 h (0·25 mg h^-1 I.V.) in sheep fetuses at a similar gestational age decreases renal renin mRNA and plasma renin concentration, respectively (Wood et al. 1984; Segar et al. 1995). However, in these earlier studies, no significant change in fetal blood pressure was observed (Wood et al. 1984; Segar et al. 1995). Dexamethasone administration to pregnant rats for 5 days increases Ao mRNA levels in both the maternal and fetal liver (Everett et al. 1991). However, in fetal sheep, 48 h of cortisol infusion (2 mg h^-1 I.P.) has been shown previously to decrease hepatic Ao gene expression (Olson et al. 1991). The duration and timing of cortisol exposure is likely to account for the differences observed in the levels of renin and Ao between the present and previous studies.

Cortisol may also raise plasma AII concentration by increasing ACE activity. In sheep and pony fetuses, an increase in plasma ACE concentration has been demonstrated towards term which coincides with the prepartum cortisol surge (Forhead et al. 1998a,b). Furthermore, ACE activity in the placenta and fetal lungs has been shown to increase with gestational age in a variety of other species (Kokubu et al. 1977; Wallace et al. 1979; Sim & Seng, 1984; Raimbach & Thomas, 1990). Although the role of cortisol in the regulation of ACE activity in fetal and placental tissues is unknown, glucocorticoids have been shown to upregulate the activity and gene expression of ACE in adult pulmonary cells in culture (Dasarathy et al. 1992).

Glucocorticoids may also influence the bioavailability of AII in utero at the level of the AT₁ receptor in both peripheral and central locations. Developmental changes in the tissue distribution of AT₁ and AT₂ receptor subtypes occur over the perinatal period, although receptor binding studies in fetal sheep appear to show that only the AT₂ receptor subtype is expressed in systemic blood vessels before birth and that AT₁ receptors primarily occur in the umbilical artery (Robillard et al. 1995; Shanmugam & Sandberg, 1996; Cox & Rosenfeld, 1999). In fetal sheep, a 48 h period of cortisol infusion has been shown previously to decrease the gene expression of the AT₁ receptor in the kidney and liver, but to increase AT₁ receptor mRNA levels in the atrium and ventricles (Segar et al. 1995). The effect of cortisol on AT₁ receptor expression in the brain and vasculature of the fetus has not been examined to date, but, in adult rats, dexamethasone is known to upregulate AT₁ receptor density and mRNA levels in aortic vascular smooth muscle cells (Sato et al. 1994a,b). A glucocorticoid-induced increase in AT₁ receptor density in fetal tissues concerned with cardiovascular function may also explain, in part, the enhanced hypotensive response to GR138950 seen in fetuses close to term and in immature cortisol-infused fetuses.

In the present study, AT₁-specific receptor blockade caused a significant increase in plasma renin concentration, the magnitude of which was dependent upon the degree of the concomitant hypotension. This rise in plasma renin was likely to be responsible for the concomitant decrease in plasma Ao concentration, and may have been stimulated by a variety of mechanisms. The normal inhibitory influence of AII on renin secretion may have been suppressed by antagonism of the AT₁ receptor responsible for mediating this effect (Iwamoto & Rudolph, 1981). Renin release may have also been activated by the drug-induced fall in blood pressure either directly via juxtaglomerular baroreceptors and/or indirectly via arterial baroreceptors and increased renal sympathetic nerve activity. Indeed, a significant relationship has been observed previously between plasma renin activity and blood pressure in sheep fetuses in which renal perfusion was lowered by aortic occlusion (Binder & Anderson, 1992). In addition, renin release may have partially increased in response to the small decrease in fetal oxygenation observed in the present study since hypoxaemia is known to be an effective stimulus in fetal sheep (Robillard et al. 1986).

The magnitude of the plasma renin response to AT₁-specific receptor blockade may have also been increased in the fetuses with a high circulating cortisol concentration by a mechanism independent of the hypotension produced. Cortisol may induce maturational changes that enhance the sensitivity of the factors responsible for renin secretion. Renal sympathetic nerve activity is increased at delivery in mature sheep fetuses and in immature fetuses after maternal antenatal treatment with dexamethasone (Segar et al. 1998). Indeed, the plasma renin responses to both haemorrhage and sodium nitroprusside-induced hypotension have been shown to increase with gestational age (Robillard et al. 1982; Rawashdeh et al. 1988). Furthermore, greater plasma renin responses to haemorrhage are observed in immature sheep fetuses after a 6 day period of cortisol infusion (Carbone et al. 1995).

The findings of the present study have implications for fetal, neonatal and adult health. First, they may explain why premature infants born before the prepartum cortisol surge often have poor cardiovascular and renal control (Vanpee et al. 1988; Watkins et al. 1989). Maturational changes in the activity of the fetal RAS normally induced by cortisol may have been circumvented by preterm delivery. Secondly, the current findings may provide a mechanism by which exposure to glucocorticoids in utero could programme hypertension in adult life. In sheep and rats, exposure of the fetus to glucocorticoids at critical periods of development has been shown to cause an increase in resting blood pressure in the adult animal (Benediktsson et al. 1993; Lindsay et al. 1996; Dodic et al. 1998). It is possible that glucocorticoids in utero may act by inducing organisational changes in the activity of the RAS which persist after birth into adult life. Indeed, previous studies have indicated that components of the RAS may be influenced permanently by the intrauterine environment. The hypertension seen in the adult offspring of rats fed a low-protein diet during pregnancy is accompanied by increased plasma and pulmonary concentrations of ACE (Langley & Jackson, 1994; Langley-Evans & Jackson, 1995). It remains to be established whether the changes in the activity of the fetal RAS induced by cortisol in the present study have long-term consequences for cardiovascular and renal function in the sheep.

	REFERENCES

Top Abstract Introduction Methods Results Discussion References

Benediktsson, R., Lindsay, R. S., Noble, J., Seckl, J. R. & Edwards, C. R. W. (1993). Glucocorticoid exposure in utero: new model for adult hypertension. Lancet 341, 339-341	[Medline]
Binder, N. D. & Anderson, D. F. (1992). Plasma renin activity responses to graded decreases in renal perfusion pressure in fetal and newborn lambs. American Journal of Physiology 262, R524-529	[Medline]
Boddy, K., Dawes, G. S., Fisher, R., Pinter, S. & Robinson, J. S. (1974). Foetal respiratory movements, electrocortical and cardiovascular responses to hypoxaemia and hypercapnia in sheep. The Journal of Physiology 243, 599-618	[Medline]
Broughton Pipkin, F., Lumbers, E. R. & Mott, J. C. (1974). Factors influencing plasma renin and angiotensin II in the conscious pregnant ewe and its foetus. The Journal of Physiology 243, 619-636	[Medline]
Broughton Pipkin, F. & Smales, O. R. C. (1977). A study of factors affecting blood pressure and angiotensin II in newborn infants. Journal of Pediatrics 91, 113-119	[Medline]
Carbone, G. M. R., Sheikh, A. U., Rogers, S., Brewer, G. & Rose, J. C. (1993). Developmental changes in renin gene expression in ovine kidney cortex. American Journal of Physiology 264, R591-596	[Medline]
Carbone, G. M. R., Sheikh, A. U., Zehnder, T. & Rose, J. C. (1995). Effect of chronic infusion of cortisol on renin gene expression and renin response to haemorrhage in fetal lambs. Pediatric Research 37, 316-320	[Abstract]
Comline, R. S. & Silver, M. (1972). The composition of foetal and maternal blood during parturition in the ewe. The Journal of Physiology 222, 233-256	[Medline]
Cox, B. E. & Rosenfeld, C. R. (1999). Ontogeny of vascular angiotensin II receptor subtype expression in ovine development. Pediatric Research 45, 414-424	[Abstract]
Craven, D. J. & Symonds, E. M. (1978). Increased renin concentration in plasma and amniotic fluid during storage. Clinical Chemistry 24, 933-935	[Abstract]
Dasarathy, Y., Lanzillo, J. J. & Fanburg, B. L. (1992). Stimulation of bovine pulmonary artery endothelial cell ACE by dexamethasone: involvement of steroid receptors. American Journal of Physiology 263, L645-649	[Medline]
Dodic, M., May, C. N., Wintour, E. M. & Coghlan, J. P. (1998). An early prenatal exposure to excess glucocorticoid leads to hypertensive offspring in sheep. Clinical Science 94, 149-155	[Medline]
Edwards, L. J., Simonetta, G., Owens, J. A., Robinson, J. S. & McMillen, I. C. (1999). Restriction of placental and fetal growth in sheep alters fetal blood pressure response to angiotensin II and captopril. The Journal of Physiology 515, 897-904	[Abstract/Full Text]
Everett, A. D., Chevalier, R. L. & Gomez, R. A. (1991). Hepatic angiotensinogen gene regulation in the fetal and pregnant rat. Pediatric Research 30, 252-255	[Abstract]
Forhead, A. J., Broughton Pipkin, F., Giussani, D. A. & Fowden, A. L. (1998a). Maturation of the renin-angiotensin system and cardiovascular function in the pony fetus. Journal of Endocrinology 159, P61 (abstract).
Forhead, A. J., Melvin, R., Balouzet, V. & Fowden, A. L. (1998b). Developmental changes in plasma angiotensin-converting enzyme concentration in fetal and neonatal lambs. Reproduction, Fertility and Development 10, 393-398.	[Medline]
Fowden, A. L., Li, J. & Forhead, A. J. (1998). Glucocorticoids and the preparation for life after birth: are there long-term consequences of the life insurance? Proceedings of the Nutrition Society 57, 113-122.	[Medline]
Gomez, R. A. & Robillard, J. E. (1984). Developmental aspects of the renal responses to hemorrhage during converting-enzyme inhibition in fetal lambs. Circulation Research 54, 301-312	[Abstract]
Ismay, M. J. A., Lumbers, E. R. & Stevens, A. D. (1979). The action of angiotensin II on the baroreflex response of the conscious ewe and conscious fetus. The Journal of Physiology 288, 467-479	[Abstract]
Iwamoto, H. S. & Rudolph, A. M. (1981). Effects of angiotensin II on the blood flow and its distribution in fetal lambs. Circulation Research 48, 183-189	[Abstract]
Kokubu, T., Ueda, E., Nishimura, K. & Yoshida, N. (1977). Angiotensin I converting enzyme activity in pulmonary tissue of fetal and newborn rabbits. Experientia 33, 1137-1138	[Medline]
Krakoff, L. R., Selvadurai, R. & Sutter, E. (1975). Effect of methylprednisolone upon arterial pressure and the renin angiotensin system in the rat. American Journal of Physiology 228, 613-617	[Medline]
Langley, S. C. & Jackson, A. A. (1994). Increased systolic blood pressure in adult rats induced by fetal exposure to maternal low protein diets. Clinical Science 86, 217-222	[Medline]
Langley-Evans, S. C. & Jackson, A. A. (1995). Captopril normalises systolic blood pressure in rats with hypertension induced by fetal exposure to maternal low protein diets. Comparative Biochemistry and Physiology 110A, 223-228.
Lindsay, R. S., Lindsay, R. M., Edwards, C. R. W. & Seckl, J. R. (1996). Inhibition of 11-hydroxysteroid dehydrogenase in pregnant rats and the programming of blood pressure in the offspring. Hypertension 27, 1200-1204	[Abstract/Full Text]
Macdonald, A. A., Colenbrander, B. & Wensing, C. J. G. (1983). The effects of gestational age and chronic fetal decapitation on arterial blood pressure in the fetus. European Journal of Obstetrics, Gynecology and Reproductive Biology 16, 63-70.	[Medline]
Nakamoto, H., Suzuki, H., Kageyama, Y., Ohishi, A., Murakami, M., Naitoh, M. & Saruta, T. (1991). Characterization of alterations of hemodynamics and neuroendocrine hormones in dexamethasone induced hypertension in dogs. Clinical and Experimental Hypertension A13, 587-606.
Olson, A. L., Robillard, J. E., Kisker, C. T., Smith, B. A. & Perlman, S. (1991). Negative regulation of angiotensinogen gene expression by glucocorticoids in fetal sheep liver. Pediatric Research 30, 256-260	[Abstract]
Phillips, I. D., Simonetta, G., Owens, J. A., Robinson, J. S., Clarke, I. J. & McMillen, I. C. (1996). Placental restriction alters functional development of the pituitary-adrenal axis in the sheep fetus during late gestation. Pediatric Research 40, 861-866	[Abstract]
Raimbach, S. J. & Thomas, A. L. (1990). Renin and angiotensin converting enzyme concentrations in the fetal and neonatal guinea-pig. The Journal of Physiology 423, 441-451	[Abstract]
Rawashdeh, N. M., Ray, N. D., Sundberg, D. K. & Rose, J. C. (1988). Comparison of hormonal responses to hypotension in mature and immature fetal lambs. American Journal of Physiology 255, R67-72	[Medline]
Rawashdeh, N. M., Rose, J. C., Rogers, M. S., Giammattei, C. & Iskandar, S. S. (1996). Immunocytochemical localization of renin in the developing ovine fetus. Reproduction, Fertility and Development 8, 97-101.	[Medline]
Reeves, J. T., Daoud, F. S. & Gentry, M. (1972). Growth of the fetal calf and its arterial pressure, blood gases, and hematologic data. Journal of Applied Physiology 32, 240-244	[Medline]
Robillard, J. E., Gomez, R. A., Meernik, J. G., Kuehl, W. D. & Van Orden, D. (1982). Role of angiotensin II on the adrenal and vascular responses to hemorrhage during development in fetal lambs. Circulation Research 50, 645-650	[Medline]
Robillard, J. E., Nakamura, K. T. & Dibona, G. F. (1986). Effects of renal denervation on renal responses to hypoxemia in fetal lambs. American Journal of Physiology 250, F294-301	[Medline]
Robillard, J. E., Page, W. V., Mathews, M. S., Schutte, B. C., Nuyt, A. M. & Segar, J. L. (1995). Differential gene expression and regulation of renal angiotensin II receptor subtypes (AT1 and AT2) during fetal life in sheep. Pediatric Research 38, 896-904	[Abstract]
Robillard, J. E., Weitzman, R. E., Burmeister, L. & Smith, F. G. (1981). Developmental aspects of the renal response to hypoxemia in the lamb fetus. Circulation Research 48, 128-138	[Abstract]
Robinson, P. M., Comline, R. S., Fowden, A. L. & Silver, M. (1983). Adrenal cortex of fetal lambs: changes after hypophysectomy and effects of synacthen on cytoarchitectures and secretory activity. Quarterly Journal of Experimental Physiology 68, 15-27	[Medline]
Sato, A., Suzuki, H., Murakami, M., Nakazato, Y., Iwaita, Y. & Saruta, T. (1994a). Glucocorticoid increases angiotensin II type 1 receptor and its gene expression. Hypertension 23, 25-30	[Abstract]
Sato, A., Suzuki, H., Nakazato, Y., Shibata, H., Inagami, T. & Saruta, T. (1994b). Increased expression of vascular angiotensin II type 1A receptor gene in glucocorticoid-induced hypertension. Journal of Hypertension 12, 511-516	[Medline]
Segar, J. L., Bedell, K., Page, W. V., Mazursky, J. E., Nuyt, A.-M. & Robillard, J. E. (1995). Effect of cortisol on gene expression of the renin-angiotensin system in fetal sheep. Pediatric Research 37, 741-746	[Abstract]
Segar, J. L., Lumbers, E. R., Nuyt, A. M., Smith, O. J. & Robillard, J. E. (1998). Effect of antenatal glucocorticoids on sympathetic nerve activity at birth in preterm sheep. American Journal of Physiology 274, R160-167	[Medline]
Shanmugam, S. & Sandberg, K. (1996). Ontogeny of angiotensin II receptors. Cell Biology International 20, 169-176	[Medline]
Sim, M. K. & Seng, K. M. (1984). Development of angiotensin converting enzyme in fetal lung and placenta of the rat and human. Clinical and Experimental Pharmacology and Physiology 11, 497-502	[Medline]
Suzuki, H., Handa, M., Kondo, K. & Saruta, T. (1982). Role of renin-angiotensin system in glucocorticoid hypertension in rats. American Journal of Physiology 243, E48-51	[Medline]
Tangalakis, K., Lumbers, E. R., Moritz, K. M., Towstoless, M. K. & Wintour, E. M. (1992). Effect of cortisol on blood pressure and vascular reactivity in the ovine fetus. Experimental Physiology 77, 709-717	[Medline]
Tetlow, H. J. & Broughton Pipkin, F. (1983). Studies on the effect of mode of delivery on the renin-angiotensin system in mother and fetus at term. British Journal of Obstetrics 90, 220-226.
Unno, N., Wong, C. H., Jenkins, S. L., Wentworth, R. A., Ding, X.-Y., Li, C., Robertson, S. S., Smotherman, W. P. & Nathanielsz, P. W. (1999). Blood pressure and heart rate in the ovine fetus: ontogenic changes and effects of fetal adrenalectomy. American Journal of Physiology 276, H248-256	[Medline]
Vanpee, M., Herin, P., Zetterstrom, R. & Aperia, A. (1988). Postnatal development of renal function in very low birthweight infants. Acta Paediatrica Scandinavica 77, 191-197	[Medline]
Wallace, K. B., Bailie, M. D. & Hook, J. B. (1979). Development of angiotensin-converting enzyme in fetal rat lungs. American Journal of Physiology 236, R57-60	[Medline]
Watkins, A. M., West, C. R. & Cooke, R. W. (1989). Blood pressure and cerebral haemorrhage and ischaemia in very low birthweight infants. Early Human Development 19, 103-110	[Medline]
Wood, C. E., Keil, L. C. & Rudolph, A. M. (1984). Physiological inhibition of ovine fetal plasma renin activity by cortisol. Endocrinology 115, 1792-1796	[Abstract]

Acknowledgements

The authors are grateful to Paul Hughes for assistance with the surgical preparation, to Averil Warren, Suzanne Cooper and Malcolm Bloomfield for the biochemical analyses, and to Alan Graham, Sue Nicholls and Ivor Cooper for the care of the animals. GR138950 and Hypertensin were gifts from Glaxo-Wellcome Research and Development Ltd and Ciba-Geigy Pharmaceuticals, respectively. A.J.F. was in receipt of a Newnham College Research Lectureship. This work was funded in part by The Royal Society.

Corresponding author

A. J. Forhead: Department of Physiology, University of Cambridge, Downing Street, Cambridge CB2 3EG, UK.

Email: ajf1005{at}cam.ac.uk

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