AJP - Regulatory, Integrative and Comparative Physiology, Vol 261, Issue 4 957-R964, Copyright © 1991 by American Physiological Society
Vasopressin-induced bradycardia in barodenervated rats
B. L. Brizzee, E. M. Adams and B. R. Walker
Department of Physiology, Tulane University School of Medicine, New Orleans, Louisiana 70112.
Experiments were performed on conscious chronically instrumented rats to
determine the contribution of baroreceptor reflex (BRR)-independent
mechanisms in the bradycardia associated with intravenous administration of
arginine vasopressin (AVP). At least 2 wk prior to experimentation, the
aortic and carotid baroreceptors were denervated in six rats. Following
recovery, the maximum bradycardic responses to pressor doses of
phenylephrine (PE) or AVP were determined on separate days in each animal.
Pulse interval (PI) was calculated from heart rate (HR), and the slopes of
PI vs. mean arterial blood pressure (MABP) and PI vs. dose were determined
for each experiment by linear regression. There was no significant
correlation of PI vs. MABP in response to bolus PE in these barodenervated
rats. However, there was a significant correlation of PI vs. MABP and PI
vs. dose in response to AVP in five of the six barodenervated rats. These
data suggest that pressor levels of AVP may elicit bradycardia independent
of the BRR. Another group of experiments was performed in the
Langendorff-isolated rat heart preparation to assess the direct
chronotropic effect of AVP. Hearts were not paced, and the coronary
arteries were perfused at a constant flow. HR was determined at various
concentrations of AVP (n = 4 at each dose). In addition, because unpaced
hearts exhibited low intrinsic rates, the same protocol was performed in
hearts receiving isoproterenol to elevate basal HR (n = 4 at each AVP
dose). There was no chronotropic effect of AVP in isolated hearts with or
without isoproterenol administration.(ABSTRACT TRUNCATED AT 250 WORDS)
