Renal nerves do not mediate vasoconstrictor responses to acute nitric oxide synthesis inhibition in conscious rats

Nitric oxide is a physiologically important peripheral and renal vasodilator. The studies presented here were conducted in the conscious, chronically catheterized, unstressed rat to investigate whether NO interacts with renal efferent sympathetic nerve activity in control of blood pressure, renal vascular resistance, and sodium excretion. Renal clearance studies were conducted in normal rats with innervated kidneys and in a separate group of rats with chronic, bilateral renal denervation. Acute systemic inhibition of NO synthesis with n-nitro L-arginine methyl ester (L-NAME) leads to hypertension, renal vasoconstriction, and natriuresis in rats with intact renal nerves. Chronic renal denervation does not diminish the pressor and renal vasoconstrictor response to NO synthesis inhibition, although the natriuretic response is prevented. Stimulation of renal NO synthesis with the substrate L-arginine produces selective renal vasodilation and a marked osmotic diuresis in the innervated kidney. Renal denervation has little impact on the responses to L-arginine. These studies suggest that in the normal, conscious, chronically catheterized rat in which the sympathetic nervous system is operating at basal levels, renal nerve activity does not contribute to the pressor or renal vasoconstrictor response to NO inhibition or the renal vasodilator response to NO stimulation. These observations contrast with earlier observations made under conditions of stress-induced activation of renal nerve activity.