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 (RP P). We examined whether administration of L-arginine, the substrate fo r nitric oxide production, restores the impaired vasa recta hemodynami c response to increases in RPP and the blunted pressure natriuresis of the spontaneously hypertensive rat (SHR). The response of descending (Q(DVR)) and ascending vasa recta blood flow (Q(AVR)) and of urinary s odium excretion (UNaV) was examined as RPP was increased by means of a n 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), Q(DVR) and Q(AVR) increased significan tly in association with increases in UN,V. In SHR receiving the inacti ve enantiomer, D-arginine (n = 7), similar increases in RPP failed to increase Q(AVR) and Q(DVR) and were associated with an attenuated incr ease in UNaV. WKY animals infused with either D-arginine or L-arginine had increases in Q(DVR), Q(AVR), 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-dependen t increases in renal medullary hemodynamics in association with restor ation of pressure natriuresis.