This article assesses the circulating levels of L-arginine, the renal response to L-arginine infusion, and the renal expression of inducible and constitutive nitric oxide synthase (NOS II and NOS III, respectively) in cirrhotic rats with ascites. Systemic and renal hemodynamics and renal function were measured in basal conditions and following two doses of L-arginine (5 and 10 mg x kg(-1) x min for 40 minutes). Renal NOS II and III messenger RNA (mRNA) expression was evaluated in basal conditions by polymerase chain reaction and Northern blot, respectively. Renal NOS II and III protein expression was assessed by Western blot and immunohistochemistry. Plasma concentration of L-arginine was significantly lower in cirrhotic rats than in control rats (48+/-11 vs. 86+/-9 micromol/L, P < .025). In both groups L-arginine infusion had no effect on systemic hemodynamics, but markedly increased renal perfusion. This effect was significantly more intense in cirrhotic rats. A very weak signal of similar intensity was found for NOS II mRNA in both groups of animals. However, no NOS II protein expression was detected. In contrast, higher NOS III mRNA abundance and protein expression, which was mainly located in the endothelial lining of the renal arterioles, were found in the kidney of cirrhotic animals. These results indicated increased renal expression of NOS III mRNA and protein, deficient circulating levels of L-arginine, and increased renal hemodynamic response to this amino acid in cirrhotic rats with ascites. Our results suggest that L-arginine supplementation at doses not affecting arterial pressure could have beneficial effects on renal perfusion in cirrhosis.