Renal effects of moderate hemorrhage in the conscious pregnant rat

Studies were performed in conscious, chronically catheterized virgin, 8- to 9-day-pregnant, and 15- to 16-day-pregnant Sprague-Dawley rats in baseline state and after removal of 7.5% total blood volume. Measurements were made of glomerular filtration rate (GFR), renal plasma flow (RPF), renal vascular resistance (RVR), arterial blood pressure (AP), and urinary electrolyte excretion. In baseline state, GFR and RPF were elevated at days 8-9 and days 15-16 of pregnancy (vs. virgins) due to a gestational renal vasodilation. The fall in hematocrit indicates substantial plasma volume expansion by days 15-16 of pregnancy. After removal of 7.5% total blood volume, little change occurred in AP in any group. However, the renal vasculature provided a sensitive response to moderate hemorrhage, since RPF fell and RVR increased similarly in virgin, 8- to 9-day- and 15- to 16-day-pregnant rats. GFR was protected in virgin and 8- to 9-day-pregnant rats but fell significantly in late pregnancy. Urinary electrolyte excretion tended to fall but was not significantly reduced by hemorrhage in any group. These studies indicate that renal vascular response to moderate hemorrhage is similar in virgin, early, and late pregnancy. Thus effector mechanisms that sense volume and regulate RVR must be continually reset to respond to progressive plasma volume expansion of pregnancy as normal.