Restoration of vasa recta hemodynamics and pressure natriuresis in SHR by L-arginine.

An increase in medullary blood flow has been implicated as a mediator of the natriuresis following increases in renal perfusion pressure (RPP). We examined whether administration of L-arginine, the substrate for nitric oxide production, restores the impaired vasa recta hemodynamic response to increases in RPP and the blunted pressure natriuresis of the spontaneously hypertensive rat (SHR). The response of descending (QDVR) and ascending vasa recta blood flow (QAVR) and of urinary sodium excretion (UNaV) was examined as RPP was increased by means of an adjustable aortic clamp placed above the renal arteries in young SHR and Wistar-Kyoto (WKY) rats. When RPP was increased in SHR receiving infusion of L-arginine (n = 7), QDVR and QAVR increased significantly in association with increases in UNaV. In SHR receiving the inactive enantiomer, D-arginine (n = 7), similar increases in RPP failed to increase QAVR and QDVR and were associated with an attenuated increase in UNaV. WKY animals infused with either D-arginine or L-arginine had increases in QDVR, QAVR, and UNaV in response to increases in RPP that were of similar magnitude to SHR receiving L-arginine. Thus the administration of L-arginine to SHR restores the pressure-dependent increases in renal medullary hemodynamics in association with restoration of pressure natriuresis.