Autoregulation of renal blood flow and glomerular filtration rate in the pregnant rabbit

Our purpose was to determine whether renal autoregulatory capability is retained in pregnancy despite the marked renal vasodilation that occurs at this time. Renal blood flow and glomerular filtration rate (GFR) were measured in anesthetized pregnant (22-27 days gestation) and nonpregnant rabbits during step reductions in renal perfusion pressure from control (100 +/- 3 mmHg) to 50 mmHg. Control renal blood flow and GFR were significantly higher in pregnant animals, averaging 65 +/- 5 and 13.1 +/- 1.1 ml/min, respectively, compared with 50 +/- 5 and 9.4 +/- 1.2 ml/min in nonpregnant rabbits. Filtration fraction was also significantly elevated in pregnant animals (0.33 +/- 0.02 vs. 0.27 +/- 0.01 in nonpregnant rabbits). During step reductions in renal perfusion pressure, renal blood flow was well autoregulated down to approximately 70 mmHg in both nonpregnant and pregnant animals, falling by only 9 +/- 4 and 12 +/- 5%, respectively. Likewise, GFR was also well autoregulated, falling by 10 +/- 2 and 8 +/- 3% in nonpregnant and pregnant animals, respectively, when perfusion pressure was reduced from 90 to 70 mmHg. These results suggest that renal autoregulation is preserved in pregnancy despite the fact that the renal circulation is already markedly vasodilated.