Abstract P188: Nephron-wide Deletion of Nos3 Impairs Salt Excretion and Causes Hypertension

Abstract

In vitro studies have suggested that nephron nitric oxide synthase 3 (NOS3) plays a role in the regulation of urinary Na + excretion (UNaV) and potentially contributes to blood pressure (BP) control. To assess whether NOS3 is indeed involved in the physiological regulation of UNaV and BP, mice with doxycycline-inducible nephron-wide deletion of NOS3 were generated. These mice were homozygous for loxP-flanked exons 9-12 of the NOS3 gene (contains the calmodulin binding site) and hemizygous for Pax8-rtTA and LC-1 transgenes (Pax8 promoter-rtTA confers nephron-specific targeting and LC-1 transgene contains doxycycline/rtTA-inducible Cre recombinase). Mice were treated with either vehicle (controls) or doxycycline (knockouts, KO) at 1 month of age for 12 days and studied at ~3 months of age. Nephron-specific NOS3 KO mice had renal-specific NOS3 gene recombination and reduced mRNA levels in microdissected nephron segments. Renal vascular NOS3 mRNA levels were markedly increased in KO mice, presumably as a compensatory response to nephron NOS3 KO. KO mice had modestly increased mean arterial pressure (100 ± 2 mmHg in controls and 103 ± 1 mmHg in KO, N=6, p<0.05) on a normal (0.3% Na + ) salt diet that increased further during high (3.2% Na + ) salt intake (103 ± 2 mmHg in controls and 118 ± 3 mmHg in KO, N=6, p<0.05). KO mice had reduced daily UNaV and greater cumulative Na + retention compared to controls over the 7 days of high salt feeding. PRC tended to be lower in KO mice on a high salt diet compared to controls (85.8 ± 13.5 ng/ml in controls and 60.1 ± 10.3 ng/ml in KO, N=12, p<0.07). Control mice excreted most of an acute I.P. salt load by 4 hr post-load, while KO mice excreted the acute salt load between 5-7 hr after loading. Furosemide, but not hydrochlorothiazide, abolished the differences in UNaV between control and control mice following an acute salt load. No sex-dependent differences in UNaV or BP were observed. In summary, these findings indicate that nephron NOS3 is involved in acute and chronic control of renal Na + excretion and BP during high salt intake. Taken together with previous studies showing that collecting duct-specific KO of NOS3 does not alter UNaV or BP, our data suggest that thick ascending limb is at least partly involved – further mechanistic studies are ongoing.