AJP - Regulatory, Integrative and Comparative Physiology, Vol 262, Issue 4 604-R609, Copyright © 1992 by American Physiological Society
Pressor effect of posterior hypothalamic stimulation is enhanced in pregnant rats
T. Hines and J. P. Porter
Department of Physiology and Biophysics, University of Louisville, Kentucky 40292.
In contrast to the attenuated pressor response to intravenous angiotensin
II (ANG II) in rat pregnancy, the response to intracerebroventricular ANG
II is not blunted. To test whether this difference was due to enhanced
effects of sympathetic nervous system activation, blood pressure, heart
rate, and renal and mesenteric blood flow were measured in conscious
term-pregnant and age-matched virgin rats during electrical stimulation of
the posterior hypothalamus and during intravenous infusion of
norepinephrine (NE). The pressor responses to endogenous NE release by
hypothalamic stimulation were significantly greater (P less than 0.05) in
pregnant rats at 10, 15 and 20 Hz. In contrast, the pressor response to
exogenous NE was significantly blunted in gravid animals. These differences
were not associated with significant differences in renal or mesenteric
vascular resistance changes. We conclude that the lack of an attenuated
response to intracerebroventricular ANG II in the pregnant rat can be
explained in part by an enhanced pressor effect of sympathetic nervous
system activation.
