Chronic Nitric Oxide Inhibition Model Six Years On

Abstract

T he discovery in 1987 that endothelium-derived nitric oxide (NO) mediates the vasodilatory effect of certain endothelium-dependent agonists 1,2 inaugurated the current huge field of NO biology.It is now recognized that NO plays essential roles in many diverse physiological processes and in some pathophysiologic events.Development of these concepts has been based largely on evidence obtained by limiting NO biosynthesis.This review is centered on the cardiovascular and particularly the renal functional and structural consequences of chronic pharmacologic NO inhibition by L-arginine analogues.We devoted special attention to the mechanisms of hypertension and organ injury that occur under these circumstances, while appreciating the inherent limitations surrounding interpretation of this data. Ubiquity and Heterogeneity of NO BiosynthesisNO is made by the enzymatic action of several widely distributed NO synthases (NOS).In the presence of the substrates L-arginine and oxygen, as well as a number of essential cofactors, NO is produced in response to appropriate stimuli.The constitutively expressed NOS play a major role in the physiological control of vascular tone and kidney function.3,4 Vascular endothelial NOS (eNOS) and brain-type NOS (bNOS) are widely distributed throughout the kidney 5 as well as the cardiovascular system and in strategic locations in the peripheral and central nervous system (CNS).6,7 Both eNOS and particularly bNOS are abundant in the kidney, glomeruli, and vasculature as well as in most segments of the tubule, 3,5 and NOS activity in medulla is considerably greater than in cortex.8 NO generated within the kidney controls the glomerular filtration rate (GFR), total renal and medullary blood flow, pressure natriuresis, epithelial sodium transport, and production of various vasoactive factors including renin.[3][4][5] eNOS is distributed throughout most parts of the arterial and venous circulation, although there is considerable heterogeneity in the extent to which NO controls tone in regional circulations.9 Although there is some basal NO release from eNOS, shear stress is the physiologically important regulator of vascular NO production.3 In the CNS, NO is made in the nucleus tractus solitarius, the paraventricular nucleus, and the ventral medulla and can control sympathetic outflow.6,10 In addition to central regulation of efferent renal sympathetic nerve activity, there is direct nitrergic innervation to several locations including the renal vasculature.7