| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
CARDIOVASCULAR |
1 Henry Wellcome L.I.N.E, University of Bristol, Whitson Street, Bristol BS1 3NY, UK
2 Department of Physiology, Bristol Heart Institute, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK
An elevation in plasma osmolality elicits a complex neurohumoral response, including an activation of the sympathetic nervous system and an increase in arterial pressure. Using a combination of in vivo and in situ rat preparations, we sought to investigate whether hypothalamic vasopressinergic spinally projecting neurones are activated during increases in plasma osmolality to elicit sympathoexcitation. Hypertonic saline (HS, I.V. bolus), which produced a physiological increase in plasma osmolality to 299 ± 1 mosmol (kg water)–1, elicited an immediate increase in mean arterial pressure (MAP) (from 101 ± 1 to 121 ± 3 mmHg) in vivo. Pre-treatment with prazosin reversed the HS-induced pressor response to a hypotensive response (from 121 ± 3 to 68 ± 2 mmHg), indicating significant activation of the sympathetic nervous system. In an in situ arterially perfused decorticate rat preparation, hyperosmotic perfusate consisted of either 135 mM NaCl, or a non-NaCl osmolyte, mannitol (0.5%); both increased lumbar sympathetic nerve activity (LSNA) by 32 ± 5% (NaCl) and 21 ± 1% (mannitol), which was attenuated after precollicular transection (7 ± 3% and 1 ± 1%, respectively). Remaining experiments used the NaCl hyperosmotic stimulus. In separate preparations the hyperosmotic-induced sympathoexcitation (21 ± 2%) was also significantly attenuated after transection of the circumventricular organs (2 ± 1%). Either isoguvacine (a GABAA receptor agonist) or kynurenic acid (a non-selective ionotropic glutamate receptor antagonist) microinjected bilaterally into the paraventricular nucleus (PVN) attenuated the increase in LSNA induced by the hyperosmotic stimulus (control: 25 ± 2%; after isoguvacine: 7 ± 2%; after kynurenic: 8 ± 3%). Intrathecal injection of a V1a receptor antagonist also reduced the increase in LSNA elicited by the hyperosmotic stimulus (control: 29 ± 6%; after blocker: 4 ± 1%). These results suggest that a physiological hyperosmotic stimulus produces sympathetically mediated hypertension in conscious rats. These data are substantiated by the in situ decorticate preparation in which sympathoexcitation was also evoked by comparable hyperosmotic stimulation. Our findings demonstrate the importance of vasopressin acting on spinal V1a receptors for mediating sympathoexcitatory response to acute salt loading.
(Received 21 June 2006;
accepted after revision 20 July 2006;
first published online 27 July 2006)
Corresponding author J. F. R. Paton: Department of Physiology, School of Medical Sciences, University of Bristol, University Walk, Bristol BS8 1TD, UK. Email: julian.f.r.paton{at}bristol.ac.uk
This article has been cited by other articles:
|
|
 |
|
  D. M. Baekey, T. E. Dick, and J. F. R. Paton Pontomedullary transection attenuates central respiratory modulation of sympathetic discharge, heart rate and the baroreceptor reflex in the in situ rat preparation Exp Physiol, July 1, 2008; 93(7): 803 - 816. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. Shi, S. D. Stocker, and G. M. Toney Organum vasculosum laminae terminalis contributes to increased sympathetic nerve activity induced by central hyperosmolality Am J Physiol Regulatory Integrative Comp Physiol, December 1, 2007; 293(6): R2279 - R2289. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. Frithiof, S. Eriksson, F. Bayard, T. Svensson, and M. Rundgren Intravenous hypertonic NaCl acts via cerebral sodium-sensitive and angiotensinergic mechanisms to improve cardiac function in haemorrhaged conscious sheep J. Physiol., September 15, 2007; 583(3): 1129 - 1143. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
K. L. Freeman and V. L. Brooks AT1 and glutamatergic receptors in paraventricular nucleus support blood pressure during water deprivation Am J Physiol Regulatory Integrative Comp Physiol, April 1, 2007; 292(4): R1675 - R1682. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 J. Qiu, S. Yao, C. Hindmarch, V. Antunes, J. Paton, and D. Murphy Transcription Factor Expression in the Hypothalamo-Neurohypophyseal System of the Dehydrated Rat: Upregulation of Gonadotrophin Inducible Transcription Factor 1 mRNA Is Mediated by cAMP-Dependent Protein Kinase A J. Neurosci., February 28, 2007; 27(9): 2196 - 2203. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
J. H. Coote Landmarks in understanding the central nervous control of the cardiovascular system Exp Physiol, January 1, 2007; 92(1): 3 - 18. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
