Role of renal medullary blood flow in the development of L-NAME hypertension in rats

The effect of chronic intravenous infusion of the nitric oxide inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME; 8.6 mg · kg^-1 · day^-1) on blood pressure, intrarenal blood flow distribution, and sodium and water balance was studied in conscious rats. On the 1st day of intravenous L-NAME infusion, renal medullary blood flow was reduced by 22%, renal cortical blood flow was unaltered, ~1 meq of sodium and 12 ml of water were retained, and blood pressure increased from 96 ± 2 to 118 ± 2 mmHg. Medullary blood flow was maintained at this decreased level, sodium continued to be retained, body weight continued to increase, and blood pressure remained elevated for the 5 days of L-NAME infusion. During the postcontrol period, blood flow in the renal medulla returned to levels not significantly different from control; the animals went into negative sodium balance and stopped gaining weight, and blood pressure returned to control. The present experiments indicate that decreased renal medullary blood flow and retention of sodium and water play an important role in the development of hypertension during chronic systemic L-NAME administration despite no measurable changes in renal cortical blood flow.