Effects of sodium nitroprusside on renal functions and NO-cGMP production in anesthetized dogs

Although the renal nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) system plays an important role in maintaining urinary sodium and water excr etion, effects of an authentic NO donor sodium nitroprusside (SNP) on urine formation have been controversial. In this study, we examined whether SNP increases renal NO release and cGMP production and induces natriuresis in t he denervated kidney of anesthetized dogs. The intrarenal arterial infusion of SNP at 10, 30, and 100 ng/kg/min did not affect renal function or NO-cG MP production. The higher dose of SNP(1,000 ng/kg/min) reduced systemic blo od pressure and urine flow rare. The antidiuresis was observed also in the contralateral control kidney, the degree of which was larger than that obse rved in the ipsilateral SNP-infused kidney. During the SNP infusion, reduct ions in urinary Na+ excretion, fractional Na+ excretion, and urinary nitrit e + nitrate excretion occurred in the control kidney but not in the SNP-inf used kidney. Urinary cGMP excretion and renal venous plasma cGMP concentrat ion were significantly increased during the SNP infusion in the SNP-infused kidney but not in the control kidney. These renal effects of SNP were simi lar to those obtained by intrarenal arterial infusion of a specific NO dono r, NOC 7 (300 ng/kg/min). These results suggest that SNP can produce nitric oxide and increase cGMP levels in the kidney and suppress sodium reabsorpt ion, but the natriuretic property of SNP may be masked by its counteracting effects including the systemic hypotension in anesthetized dogs.