AJP - Heart and Circulatory Physiology, Vol 249, Issue 3 450-H456, Copyright © 1985 by American Physiological Society
Hypotension 1.5 min after 10% hemorrhage permits evaluation of rabbit's baroreflex
T. Yamazaki and K. Sagawa
In seven chronically instrumented rabbits, we studied the influence of the
vasopressin system on the evaluation of acute reflex compensation of
arterial pressure for a mild hemorrhage. Rabbits were bled 10% of estimated
blood volume in 1 min. The hemorrhage was repeated before and after
administration of a vasopressin antagonist [d(CH2)5Tyr(Me)arginine
vasopressin, 10 micrograms/kg] and in the conscious and anesthetized
(pentobarbital sodium 20 mg/kg) state. The efficacy of the vasopressin
antagonist was preliminarily tested in each rabbit by confirming its
antagonism against the hemodynamic effects of infused vasopressin (50 ng X
min-1 X kg-1). Mean arterial pressure (MAP), heart rate (HR), mean aortic
flow (MAF), and total peripheral resistance (TPR) were measured before and
at 1.5 min after completion of hemorrhage. The hemorrhage caused
statistically significant decrease in MAP (84 +/- 6 to 78 +/- 6 mmHg) and
MAF (195 +/- 28 to 158 +/- 26 ml X kg-1 X min-1) and increase in TRP (0.44
+/- 0.05 to 0.51 +/- 0.07 mmHg X kg X min X ml-1) and HR (271 +/- 21 to 284
+/- 22 beat/min). However, there was no statistically significant
interaction in any variables between vasopressin and hemorrhage, i.e.,
whether vasopressin was blocked or intact did not affect the fall in MAP by
hemorrhage. We conclude that in the rabbit vasopressin's role in the acute
compensation of arterial pressure for a quick 10% hemorrhage is small
enough to permit accurate estimation of the arterial baroreflex gain from
the depressor responses to mild hemorrhage with and without the reflex
function.
