Abstract-Nitric oxide (NO) plays important roles in the regulation of renal function and the long-term control of blood pressure. New roles of NO have been proposed recently in diabetes, nephrotoxicity, and pregnancy. NO derived from all 3 NOS isoforms contributes to the overall regulation of kidney function, and recent advances in our understanding of their regulation have been made lately. In this regard, substrate and cofactor availability play important roles in regulating nitric oxide synthase (NOS) activity not only by limiting enzyme activity but also by influencing the coupling of NOS with its cofactors, tetrahydrobiopterin and NADPH. Protein-protein interactions are now recognized to be important negative and positive regulators of NOS. Phosphorylation is another component of the mechanism whereby NOS is activated or deactivated. Increased NOS expression can also influence enzyme activity; however, the degree of expression does not always correlate with enzyme activity because increased NO levels can result in inhibition of NOS. Finally, other potential regulators of NOS such as endogenous L-arginine analogs may also be important. In this article, we summarize recent advances in the regulation of activity and expression of the NOS isoforms within the kidney. renal function and long-term regulation of blood pressure. [1][2][3][4] This is best evidenced by the fact that inhibiting intrarenal NO production increased blood pressure. 5 In addition, reduced NO has been identified as a common denominator of many hypertensive models. 6 -9 The effects of NO on blood pressure via actions in the kidney occur through multiple mechanisms. These include increasing renal blood flow caused by vasodilatation, 10 increasing glomerular filtration, 11 inhibiting sodium transport along the nephron, 12-14 and regulating release of renin. 15 NO produced by each of the 3 nitric oxide synthases (NOS), NOS 1, NOS 2, and NOS 3, reportedly contributes to the regulation of renal function. Inhibition of NOS activity within the kidney is known to lead to sodium retention and hypertension. This review addresses recent advances in our understanding of the role played by renal NO in various physiological and pathophysiological conditions, as well as how NO production is regulated.
Roles for Renal NOHistorically, NO produced by the kidney has been thought of primarily as a factor that regulates urinary volume and sodium excretion. The physiological effects of NO can be mediated via changes in renal hemodynamics and/or salt and water absorption by the nephron. NO reduces renal vascular tone in part by dilating the afferent arteriole. 16 It also increases glomerular filtration rate. 11 NO modulates renin secretion by the juxtaglomerular apparatus 15 and tubuloglomerular feedback. 3 Finally, NO regulates transport in various nephron segments as reviewed recently by Ortiz and Garvin. 12 More recently it has been recognized that in a number of pathophysiological conditions, the actions of NO on renal hemodynamics and/or nephron transport are ...