| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1Department of Physiology, The Medical School, University of Birmingham, Birmingham B15 2TT, UK2Department of Physiology, University College Cork, Cork, Ireland
The present study investigated the effect of acute hypothermia on baroreflex control of heart rate (HR) and renal sympathetic nerve activity (RSNA) by generating baroreflex logistic function curves, using bolus doses of phenylephrine and sodium nitroprusside, in anaesthetized male Wistar rats at a core temperature (Tb) of 37°C, during acute severe hypothermia at Tb= 25°C and on rewarming to 37°C. Comparisons were made between rats without (euthermic, n= 6) and with (acclimated, n= 7) prior exposure to lower ambient temperatures and shorter photoperiod, simulating adaptation to winter conditions. In both groups of rats, acute hypothermia to Tb= 25°C shifted the baroreflex-RSNA curve slightly leftwards and downwards with decreases in the setpoint pressure and maximal gain, whereas it markedly impaired the baroreflex-HR curve characterized by decreases in response range by 
90% (P < 0.001), minimum response by 10% (P < 0.05) and maximum gain by 95% (P < 0.001), from that at Tb= 37°C. All parameters were restored to precooling levels on rewarming. Electrical stimulation of cardiac vagal efferents induced a voltage-related bradycardia, the magnitude of which was partially reduced during acute hypothermia, and there was a significant prolongation of the electrocardiogram intervals indicating a delay in cardiac conduction. Mild suppression of baroreflex control of RSNA could contribute to hypothermic hypotension and may primarily reflect an effect of Tb on central drive. The marked attenuation of the baroreflex control of HR during hypothermia was likely to be due to an impairment of both the central and peripheral components of the reflex arc. Baroreflex control of RSNA and HR was similar between both groups of rats, which implied that the control was non-adaptive on chronic cold exposure.
(Received 10 December 2003;
accepted after revision 18 February 2004;
first published online 20 February 2004)
Corresponding author S. Egginton: Department of Physiology, The Medical School, University of Birmingham, Vincent Drive, Birmingham B15 2TT, UK. Email: s.egginton{at}bham.ac.uk
This article has been cited by other articles:
|
|
 |
|
  V. Orea, R. Kanbar, B. Chapuis, C. Barres, and C. Julien Transfer function analysis between arterial pressure and renal sympathetic nerve activity at cardiac pacing frequencies in the rat J Appl Physiol, March 1, 2007; 102(3): 1034 - 1040. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 B. G. Helwig, S. Parimi, C. K. Ganta, R. Cober, R. J. Fels, and M. J. Kenney Aging alters regulation of visceral sympathetic nerve responses to acute hypothermia Am J Physiol Regulatory Integrative Comp Physiol, September 1, 2006; 291(3): R573 - R579. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
