Nitric oxide and the immature kidney.

Nitric oxide (NO) is a very potent vasodilator synthesized from L-arginine by endothelial cells. By activating guanylate cyclase, it promotes vasodilatation of adjacent smooth muscle cells. NO is thus involved in the control of vascular tone in various organs. There is increasing evidence that NO is tonically synthesized within the kidney and plays a crucial role in the modulation of renal hemodynamics and excretory function. The blockade of basal NO synthesis has been shown to result in decreases in renal blood flow and, to a lesser extent, in glomerular filtration rate. NO may also be involved in sodium excretion. In the neonatal period, a time associated with a hyperactivation of vasoactive systems, NO seems to play a greater role than in the adult. It could also be implicated in the response to vasoconstrictive stresses, such as perinatal hypoxia, frequently encountered during this period.