Nephron-Specific Disruption of Nitric Oxide Synthase 3 Causes Hypertension and Impaired Salt Excretion.

Background: In vitro studies suggest that nephron nitric oxide synthase 3 (NOS3) modulates tubule Na transport.

Methods And Results: To assess nephron NOS3 relevance in vivo, knockout (KO) mice with doxycycline-inducible nephron-wide deletion of NOS3 were generated. During 1 week of salt loading, KO mice, as compared with controls, had higher arterial pressure and Na retention, a tendency towards reduced plasma renin concentration, and unchanged glomerular filtration rate. Chronic high salt-treated KO mice had modestly decreased total NCC and total SPAK/OSR1 versus controls, however percent phosphorylation of NCC (at T) and of SPAK/OSR1 was increased. In contrast, total and phosphorylated NKCC2 (at T) were suppressed by 50% each in KO versus control mice after chronic salt intake. In response to an acute salt load, KO mice had delayed urinary Na excretion versus controls; this delay was completely abolished by furosemide, partially reduced by hydrochlorothiazide, but not affected by amiloride. After 4 hours of an acute salt load, phosphorylated and total NCC were elevated in KO versus control mice. Acute salt loading did not alter total NKCC2 or SPAK/OSR1 in KO versus control mice but increased the percent phosphorylation of NKCC2 (at T and S) and SPAK/OSR1 in KO versus control mice.

Conclusions: These findings indicate that nephron NOS3 is involved in blood pressure regulation and urinary Na excretion during high salt intake. Nephron NOS3 appears to regulate NKCC2 and NCC primarily during acute salt loading. These effects of NOS3 may involve SPAK/OSR1 as well as other pathways.