Renin regulation by nitric oxide

肾素-血管紧张素系统产生有效的血管收缩剂血管紧张素II，其参与调节血管阻力、血压和几乎所有形式的高血压。 肾素是血管紧张素形成的限速酶步骤。 在肾脏中，血管紧张素引起的血管收缩被血管舒张剂内皮衍生的一氧化氮（NO）缓冲。 我们认为，NO既能抵消血管紧张素诱导的血管收缩，又能通过差异调节肾素分泌来调节血管收缩的形成。 据报道，NO既能抑制又能刺激肾素分泌，但这些不同的作用是如何发生的尚不清楚。 虽然环核苷酸刺激肾素分泌的cAMP，我们假设cGMP，NO的第二信使，抑制肾素释放时，cAMP水平低激活蛋白激酶GI！（PKGII）和增加JG细胞内钙。 相比之下，当cAMP被促分泌素如前列腺素（PG）E增加时，cGMP通过抑制磷酸二酯酶（PDE）-3间接刺激肾素释放，并通过减少其代谢来夸大cAMP的作用。 在目标1中，我们提出，低cAMP水平，NO抑制肾素刺激cGMP的生产和增加PKGII活性的JG细胞。 我们将在体外（分离的JG细胞和分离的肾小球的原代培养物）和体内使用eNOS敲除小鼠研究NO和cGMP对肾素的影响，而不刺激cAMP。 在目标2中，我们提出，如果cAMP水平升高，NO通过cGMP抑制PDE-3和增强cAMP介导的肾素刺激来增强肾素释放。 我们将使用原代JG培养物、分离的肾小球（无致密斑）和肾皮质切片（有致密斑）研究cAMP和致密斑对肾素的刺激，阻断破坏cGMP或cAMP的PDE。 我们将使用nNOS敲除小鼠来观察来自致密斑的NO是否介导肾素刺激。 在目的3中，我们提出前列腺素类，特别是由考克斯-2在斑致密产生的PGE 2，调节JG细胞中的cAMP水平。 考克斯-2和nNOS在致密斑中的共表达表明NO对肾素的作用依赖于考克斯-2的表达和活性。 我们将操纵考克斯-2的表达和PG的合成在致密斑和研究NO和cGMP的影响，使用肾皮质切片和体内实验刺激致密斑介导的大鼠和nNOS敲除小鼠的肾素分泌。 这些研究应揭示NO抑制或刺激肾素分泌的双重途径。

The renin-angiotensin system produces the potent vasoconstrictor angiotensin II, which is involved in i regulation of vascular resistance, blood pressure, and virtually every form of hypertension. Renin is the rate-i limilmg enzymatic step in angiotensin formation. In the kidney, the vasoconstriction by angiotensin is buffered by the vasodilator endothelium-derived nitric oxide (NO). We propose that NO both counteracts angiotensin-induced vasoconstriction and regulates its formation by differentially regulating renin secretion. NO has been reported to both inhibit and stimulate renin secretion, but it is unclear how these different effects could occur. While the cyclic nucleotide which stimulates renin secretion is cAMP, we hypothesize that cGMP, the second messenger of NO, inhibits renin release when cAMP levels are low by activating protein kinase GI! (PKGII) and increasing JG cell intracellular calcium. In contrast, when cAMP is increased by secretagogues such as prostaglandin (PG)E, cGMP stimulates renin release indirectly by inhibiting phosphodiesterase (PDE)-3 and exaggerating cAMPs effects by reducing its metabolism. In aim 1, we propose that with low cAMP levels, NO inhibits renin by stimulating cGMP production and increasing PKGII activity in the JG cells. We will study effects of NO and cGMP on renin without stimulating cAMP both in vitro (primary cultures of isolated JG cells and isolated glomeruli) and in vivo using eNOS knockout mice. In aim 2, we propose that if cAMP levels are elevated, NO enhances renin release by cGMP inhibition of PDE-3 and potentiation of cAMP-mediated renin stimulation. We will study cAMP and macula densa stimulation of renin, blocking PDEs that break down either cGMP or CAMP, using primary JG cultures, isolated glomeruli (without the macula densa) and renal cortical slices (with the macula densa). We will use nNOS knockout mice to see if NO from the macula densa mediates renin stimulation. In aim 3 we propose that prostanoids, particularly PGE2 produced by COX-2 in the macule dense, regulate cAMP levels in JG cells. Co-expression of COX-2 and nNOS in the macula densa suggests NO's effect on renin depends on COX-2 expression and activity. We will manipulate COX-2 expression and PG synthesis in the macula densa and study the effects of NO and cGMP, using renal cortical slices and in vivo experiments stimulating macula densa-mediated renin secretion in rats and nNOS knockout mice. These studies should reveal the dual pathways by which NO can either inhibit or stimulate renin secretion.