AJP - Regulatory, Integrative and Comparative Physiology, Vol 257, Issue 4 909-R916, Copyright © 1989 by American Physiological Society
Role of hemodynamic factors in osmoregulatory alterations of rat pregnancy
W. M. Barron, J. A. Durr, R. W. Schrier and M. D. Lindheimer
Department of Medicine, Pritzker School of Medicine, University of Chicago, Illinois 60637.
Plasma osmolality (Posmol) decreases in pregnancy, possibly because of
hemodynamically mediated arginine vasopressin (AVP) secretion, i.e.,
inadequate vascular filling and/or decreased blood pressure. This
hypothesis was tested in Sprague-Dawley rats treated on gestational days
1-18 or 13-18 with 1) deoxycorticosterone acetate (DOCA) + standard chow
(0.5% Na), 2) vehicle + standard chow, or 3) high-Na (1.25%) diet. Renal
sodium "escape" and suppression of the renin-aldosterone system suggested
"effective volume expansion," yet Posmol was similar in all pregnant
groups, 7-10 mosmol/kg below levels in virgin controls, and plasma AVP was
unaltered. Apparent osmotic thresholds for AVP secretion, similar in
control and DOCA-treated gravid animals, were 8-10 mosmol/kg below those of
untreated virgin rats. Norepinephrine + DOCA, administered to gravid
animals consuming normal or high-Na chow, increased blood pressure
approximately 10% above control levels, but this also failed to alter
Posmol. These data suggest that mechanisms other than hemodynamically
mediated AVP secretion are responsible for the osmoregulatory alterations
accompanying rodent pregnancy.
