Abstract P200: Role of Macula Densa Neuronal Nitric Oxide Synthase in Control of Renin Release and Blood Pressure Recovery Following Hemorrhagic Shock

Abstract

Renin is a rate limiting factor for generation of angiotensin II, which is essential for blood pressure regulation. The role of macula densa nitric oxide (NO) in renin release is not conclusive. The goal of this study was to elucidate the role of macula densa neuronal NO synthase (NOS1) in control of renin release in response to sodium challenges and hemorrhagic shock, as well as in blood pressure recovery after hemorrhagic shock. C57BL/6L mice and macula densa specific NOS1 knockout (MD-NOS1KO) mice were given 10 days of low (0.1% NaCl), normal (0.4% NaCl) and high (1.4% NaCl) sodium diet. Hemorrhagic shock was induced by withdrawing 0.4 ml whole blood from the right retro-orbital sinus. Mean arterial pressure (MAP) in conscious mice was monitored by radio-telemetry system. Plasma renin concentration (PRC) was determined by radioimmunoassay. Low sodium diet stimulated PCR by 29% (from 685 ± 32 to 883 ± 112 ng/ml/hr) in WT mice and by 16% (from 652 ± 24 to 756 ± 124 ng/ml/hr) in the MD-NOS1KO mice (n=5/group, p<0.01 vs WT). PCR was not significantly different between the WT and MD-NOS1KO mice fed a normal or high salt diet. As shown in Fig1A, following removal of 0.4ml of blood, MAP dropped to about 40mmHg in the WT mice and 35mmHg in the MD-NOS1KO mice. MAP recovered faster in WT mice than the MD-NOS1KO mice. In Fig1B, PRC increased over 200% of the basal value in WT mice, but only increased about 26% in the MD-NOS1KO mice (n=4/group, p<0.01 vs WT). We conclude that NOS1 in the macula densa facilitates renin release. Lack of macula densa NO generation impairs blood pressure recovery, which may be mediated by limiting renin release during hemorrhagic shock.