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，它参与调节血管阻力、血压和几乎所有形式的高血压。肾素是血管紧张素形成过程中限速的酶促步骤。在肾脏中，血管紧张素引起的血管收缩被血管扩张剂内皮源性一氧化氮（NO）所缓冲。我们认为一氧化氮既可以抵消血管紧张素引起的血管收缩，又可以通过调节肾素分泌来调节血管收缩。据报道，一氧化氮可以抑制和刺激肾素分泌，但目前尚不清楚这些不同的作用是如何发生的。而刺激肾素分泌的环核苷酸是cAMP，我们假设cGMP， NO的第二信使，通过激活蛋白激酶GI，在cAMP水平低时抑制肾素的释放！（PKGII）和增加JG细胞内钙。相反，当前列腺素（PG）E等促分泌物增加肾素时，cGMP通过抑制磷酸二酯酶(PDE)-3间接刺激肾素释放，并通过降低其代谢来夸大cAMP的作用。在目的1中，我们提出在低cAMP水平下，NO通过刺激JG细胞中cGMP的产生和增加PKGII活性来抑制肾素。我们将在体外（分离的JG细胞和分离的肾小球的原代培养）和体内使用eNOS敲除小鼠研究NO和cGMP在不刺激cAMP的情况下对肾素的影响。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、分离肾小球（没有黄斑）和肾皮质切片（有黄斑）来研究cAMP和肾素对黄斑致密区的刺激，阻断分解cGMP或cAMP的PDEs。我们将使用nNOS敲除小鼠来观察来自黄斑致密的NO是否介导肾素刺激。在目标3中，我们提出前列腺素，特别是由COX-2在斑块致密中产生的PGE2，调节JG细胞中的cAMP水平。COX-2和nNOS在黄斑致密中的共同表达表明NO对肾素的影响取决于COX-2的表达和活性。我们将利用大鼠和nNOS敲除小鼠的肾皮质片和体内实验刺激黄斑介导的肾素分泌，调控COX-2在致密斑中的表达和PG合成，研究NO和cGMP的影响。这些研究应该揭示一氧化氮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.