Surgical correction of renal artery stenosis in Goldblatt hypertension rapidly normalizes blood pressure and increases renal function. This study was conducted in 1-kidney, 1 clip (1K1C) Goldblatt hypertensive rats to examine whether the unclipping-induced reversal of blood pressure and renal function is mediated by nitric oxide (NO). The 1K1C rats were prepared and given tap water with or without supplementation of NG-nitro-L-arginine methyl ester (L-NAME). Systolic blood pressure (SBP) before and after renal artery clipping was measured with the tail-cuff method. Four weeks later, surgical unclipping was performed while blood pressure and renal function responses were determined. The results show that clipping the renal artery for 4 weeks increased SBP from 140+/-5 to 183+/-6 mm Hg (P<0.05). Concurrent L-NAME treatment accelerated and aggravated the clipping-induced increases in SBP from 138+/-6 to 219+/-8 mm Hg (P<0.05). Surgical unclipping reduced blood pressure to normotensive levels within 2 hours in all hypertensive rats with and without chronic or acute L-NAME treatment. However, the magnitude of reductions in blood pressure in the initial 1 hour after unclipping was significantly less in L-NAME-treated rats than in nontreated rats (9+/-2% versus 16+/-1%, P<0.05). Despite reducing blood pressure, unclipping significantly increased glomerular filtration rate, urine flow, and sodium and potassium excretions, but the extent of the increases in these renal functions was significantly attenuated in L-NAME-treated rats. These data suggest that NO production partly contributes to the hypotensive and renal responses to unclipping but does not mediate the reversal of renovascular hypertension of this model.