Impaired renin response to hemorrhage in hypertensive rabbits.
Courneya, C. A.
Department of Physiology, University of British Columbia, Vancouver
B.C. V6T 1Z3
APStracts 3:0183H, 1996.
It is not known how the intrarenal mechanisms which control Renin
release, in particular the intra-renal receptor, respond to the
structural changes in renal vasculature which are secondary to
hypertension. It is also not known whether baroreflex control of
Renin release is affected by hypertension. We hypothesized impairment
at both levels. Thus we compared Plasma Renin Activity (PRA) during
hemorrhage between conscious normotensive (NT) and renal wrap
hypertensive (HT) rabbits. Mean Arterial Pressure (MAP) and PRA were
measured prior to and during hemorrhage at 4 ml/min. To look at
intrarenal control of Renin we hemorrhaged NT and HT rabbits after
pharmacological Autonomic Nervous System (ANS) Blockade, thus
eliminating the influence of reflexes. The slope of the logPRA-MAP
relationship was significantly (p<0.002) reduced in ANS-Blocked
HT rabbits as compared to NT rabbits. In other words for a given fall
in MAP the HT rabbits had lower plasma levels of PRA. To examine
baroreflex control of Renin we hemorrhaged rabbits with an intact
ANS. The slope of the logPRA-MAP relationship was significantly
attenuated (p<0.0087) in ANS Intact HT rabbits compared to NT
rabbits. Cardiac Receptor Denervation had no effect on the slope of
this relationship for either NT or HT rabbits, indicating no
appreciable role for Cardiac Receptors in the reflex control of Renin
under these circumstances. Although Sinoaortic Denervation
significantly attenuated the slope of the logPRA-MAP relationship
(suggesting an important role in reflex control of Renin) it did so
equally in NT (p<0.0261) and HT (p<0.0189) rabbits. We
concluded that Renin release was impaired in ANS Blocked HT rabbits
and that the impairment may be due to dysfunction of intra-renal
mechanisms (for example: the intra-renal receptor). These results
also support the hypothesis that reflex control of PRA was impaired
in HT rabbits, however, no particular role could be ascribed to
either the cardiac or arterial baroreceptors in contributing to this
impairment.
Received 22 June 1995; accepted in final form 3 April 1996.
APS Manuscript Number H567-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 8 May 96