Endothelial Derived Relaxing Factor Controls Renal Hemodynamics in the Normal Rat Kidney

These studies were conducted in the conscious, chronically catheterized rat to determine whether the endothelial derived relaxing factor (EDRF) controls renal function in the normal state. Administration of the EDRF synthesis inhibitors N-monomethyl-L-arginine (NMA; 100 mg/kg body weight) or N-nitro-L-arginine methylester (NAME; 10 mg/kg body wt) led to a large, sustained rise in blood pressure, a large rise in renal vascular resistance, a fall in renal plasma flow, a relatively slight reduction in glomerular filtration rate, and a consequent rise in filtration fraction. In addition, a marked natriuresis occurred because of a reduction in the fractional reabsorption of sodium. In separate studies, a continuous infusion of excess L-arginine (300 mg/kg body wt bolus followed by 50 mg/kg body wt per min) attenuated the NMA- or NAME-induced rise in blood pressure and reversed the renal hemodynamic effects such that a significant rise in renal plasma flow was seen. L-Arginine alone produced a selective renal vasodilation and large increases in sodium excretion. These observations support earlier suggestions that tonic release of EDRF controls the basal blood pressure and also show that renal function in the normal unstressed rat is markedly influenced by EDRF. These studies suggest that, in addition to controlling renal plasma flow, EDRF may have other, complex actions at the glomerulus. The natriuresis seen after acute inhibition of EDRF with NMA or NAME was probably the result of a pressure natriuretic response to the abrupt rise in blood pressure and also, perhaps, reflects removal of an EDRF influence to directly enhance sodium reabsorption somewhere in the nephron.