Abstract 039: Blockade of Macula Densa NOS1 Decreases GFR and Promotes the Development of Hypertension During Pregnancy

Abstract

We hypothesized that neuronal nitric oxide synthesis (NOS1) β in the macula densa promotes the renal hemodynamic changes during normal pregnancy and inhibition of macula densa NOS1 induces hypertension during pregnancy. First, we measured the protein levels of NOS1β in the renal cortex, which increased by 11.5±1.7 folds in pregnant mice (n=5) compared with virgin mice (n=7, p<0.01 vs virgin), while there was no change in NOS1α. Then, in isolated and perfused juxtaglomerular apparatus, we measured tubuloglomerular feedback (TGF)-induced NO generation by the macula densa, which increased by 66.7±6.1% in pregnant mice (n=5) compared with the virgin mice (n=5, p<0.01 vs virgin). We next measured TGF in vivo using micropuncture, which was 3.6±0.3 mmHg in mice at day 19 of pregnancy (n=3) and 5.5±0.7 mmHg in virgin mice (n=7, p<0.05 vs virgin). To determine the significance of the macula densa NOS1, we measured glomerular filtration rate (GFR) and mean arterial pressure (MAP) with telemetry in macula densa specific NOS1 knockout (KO) mice (NKCC2 cre ; NOS1 flox/flox ) and WT (NOS1 flox/flox ) mice. In the WT mice, GFR raised by 25.7±1.1% while the MAP decreased by 6.1±2.7 mmHg at day 18 of pregnancy (n=7, p<0.01). The elevations in GFR were largely blunted in KO mice with only a 13.7±2.8% increase while MAP gradually rose by 28.2±3.3 mmHg above basal level at day 18 of pregnancy (n=5, p<0.05 vs baseline). Finally, we examined macula densa NOS1 in a mouse model of preeclampsia, a reduced uterine perfusion pressure (RUPP) model. At day 19 of pregnancy, the protein levels of NOS1β decreased 71.4±9.6% (n=5), NO generation reduced 26.7±5.8% (n=5) and TGF in vivo increased 41.6±12.2% (n=3) in RUPP mice, compared with normal pregnant mice (p<0.05). Moreover, the MAP or GFR was no significant different between the pregnant KO mice with RUPP and the pregnant KO mice. In conclusion, upregulated macula densa NOS1β blunts TGF response and promotes elevation of GFR during normal pregnancy. In contrast, downregulation of NOS1β in the macula densa enhances the TGF response, decreases GFR and promotes hypertension during pregnancy. These results suggest that inhibition of macula densa NOS1β could be an important mechanism mediating the decrease in GFR and elevation in MAP in preeclampsia.