Role of neuronal nitric oxide synthase in mediating renal hemodynamic changes during pregnancy

Renal plasma flow (RPF) and glomerular filtration rate (GFR) are markedly i ncreased during pregnancy. We recently reported that the renal hemodynamic changes observed during pregnancy in rats are associated with enhanced rena l protein expression of neuronal nitric oxide synthase (nNOS). The purpose of this study was to determine the role of nNOS in mediating renal hemodyna mic changes observed during pregnancy. To achieve this goal, we examined th e effects of the nNOS inhibitor 7-nitroindazole (7-NI) on kidney function i n normal conscious, chronically instrumented virgin (n = 6) and pregnant ra ts (n = 9) at day 16 of gestation. Infusion of 7-NI had no effect on RPF (4 .7 +/- 0.7 vs. 4.8 +/- 0.9 ml/min), GFR (2.2 +/- 0.2 vs. 2.5 +/- 0.4 ml/min ), or mean arterial pressure (MAP; 127 +/- 7 vs. 129 +/- 10 mmHg) in virgin rats. In contrast, 7-NI infused into pregnant rats decreased RPF (8.9 +/- 1.6 vs. 6.5 +/- 1.4 ml/min) and GFR (4.4 +/- 0.7 vs. 3.3 +/- 0.7 ml/min) wh ile having no effect on MAP (123 +/- 4 vs. 123 +/- 3 mmHg). In summary, inh ibition of nNOS in pregnant rats at midgestation results in significant dec reases in RPF and GFR. nNOS inhibition in virgin rats had no effect on rena l hemodynamics. These data suggest that nNOS may play a role in mediating t he renal hemodynamic changes that occur during pregnancy.