The effects of NG-nitro-L-arginine, a nitric oxide synthase inhibitor, on norepinephrine overflow and antidiuresis induced by stimulation of renal nerves in anesthetized dogs.

We examined the involvement of endogenous nitric oxide (NO) in noradrenergic neurotransmission and renal function in anesthetized dogs, by using NG-nitro-L-arginine (NOARG), a NO synthase inhibitor. Renal nerve stimulation (RNS) produced the frequency-dependent increase in the rate of norepinephrine secretion. The low frequency RNS (0.5-2.0 Hz) decreased urine flow and urinary excretion of sodium, without affecting renal hemodynamics. High frequency RNS (2.5-5.0 Hz) caused a more potent antidiuresis and renal vasoconstriction that resulted in reductions in renal blood flow and glomerular filtration rate. Intrarenal arterial infusion of NOARG, at a dose (10 micrograms/kg/min) which had no effect on renal hemodynamics, significantly enhanced the RNS-induced reductions of urine formation and renal vasoconstriction and increments in norepinephrine secretion rate. Qualitatively similar results were observed with a higher dose of NOARG (40 micrograms/kg/min), although this dose did decrease basal levels of renal blood flow and urine flow. Enhancement of NOARG on RNS-induced actions was abolished by the simultaneous administration of L-arginine. Endogenous NO probably has a role as inhibitory modulator of renal noradrenergic neurotransmission.