AJP - Heart and Circulatory Physiology, Vol 240, Issue 6 908-H913, Copyright © 1981 by American Physiological Society
Effect of volume expansion on pressor response to angiotensin II in pregnant ewes
S. Matsuura, R. P. Naden, N. F. Gant Jr, C. R. Parker Jr and C. R. Rosenfeld
Vascular refractoriness to infused angiotensin II (AII) characterizes
normal human and ovine pregnancy. To ascertain whether the refractoriness
in the gravid ewe is mediated by either endogenous plasma concentrations of
renin and AII or vasomotor reflexes, effects of acute volume expansion (VE)
on the pressor response to AII were studied in chronically instrumented
nonpregnant and near-term pregnant sheep. Dose-response curves describing
the pressor response (delta BP) were determined before and after infusions
of 1.0 1 of isotonic saline (NS) or 0.5 1 of 10% dextran (D). In
nonpregnant sheep, hematocrit (Hct) and plasma renin activity (PRA) fell in
all animals after NS (n = 7) and D (n = 6) (P less than 0.005). After VE
with NS and D, delta BP increased at each dose of AII (P less than 0.05).
The pressor response to AII in pregnant sheep was not altered by NS
although decreases in Hct and PRA were comparable to those in nonpregnant
sheep. Baroreceptor responses were not altered. Vascular refractoriness to
infused AII in pregnant sheep is not due primarily to changes in plasma
concentrations of renin-AII but more likely to another factor, vessel wall
refractoriness. In this respect, the ewe is similar to the human.
