Although the renal nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) system plays an important role in maintaining urinary sodium and water excretion, 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 the 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-cGMP production. The higher dose of SNP (1,000 ng/kg/min) reduced systemic blood pressure and urine flow rate. The antidiuresis was observed also in the contralateral control kidney, the degree of which was larger than that observed in the ipsilateral SNP-infused kidney. During the SNP infusion, reductions in urinary Na+ excretion, fractional Na+ excretion, and urinary nitrite + nitrate excretion occurred in the control kidney but not in the SNP-infused kidney. Urinary cGMP excretion and renal venous plasma cGMP concentration were significantly increased during the SNP infusion in the SNP-infused kidney but not in the control kidney. These renal effects of SNP were similar to those obtained by intrarenal arterial infusion of a specific NO donor, 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 reabsorption, but the natriuretic property of SNP may be masked by its counteracting effects including the systemic hypotension in anesthetized dogs.
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