Possible mechanisms for changes in renal hemodynamics during pregnancy: studies from animal models.

Glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) increase during gestation in humans, rats, rabbits, dogs, and sheep. Serial studies performed in chronically instrumented conscious pregnant rats show that the relative time course of changes in renal hemodynamics resembles that of human pregnancy. Because gestational alterations of renal hemodynamics in humans are similar to those in other mammalian species, animal models are being used to investigate possible mechanisms for these changes. In gravid rats and rabbits, vasodilatory prostaglandins most likely do not mediate the increase of GFR and ERPF. Chronic administration of prolactin has been tested in nonpregnant rats, and although some studies suggest that this hormone can augment renal hemodynamics, others do not. The decline in GFR and ERPF, which in rats occurs close to term despite ongoing increments of plasma volume, does not appear to be mediated by angiotensin II. Cyclic guanosine 3',5'-monophosphate (cGMP) is increased in the plasma of pregnant rats, and urinary excretion rates are also enhanced. Research is presently continuing to determine if intracellular and/or extracellular cGMP contribute to the vasodepressor phenomena observed during pregnancy.