Kidneys of control and arthritic rats were perfused with a hemoglobin-free perfusion fluid with simultaneous monitoring of perfusion pressure and oxygen uptake. The basal values of renal perfusion pressure were 76.3 +/- 4.63 and 59.96 +/- 3.65 mm Hg in control and arthritic rats, respectively. Infusion of 100 microM Nomega-nitro-L-arginine methyl ester (L-NAME) an inhibitor of constitutive and inducible nitric oxide synthase, increased the renal perfusion pressure to 91.6 +/- 5.52 and 106.69 +/- 8.47 mm Hg in control and arthritic rats, respectively. Oxygen uptake of kidneys from control rats was 2.48 +/- 0.74 micromol min(-1) g(-1) and that of the arthritic rats was 2.44 +/- 0.75 micromol min(-1) g(-1). These results are consistent with an increased production of hemodynamically active nitric oxide in kidneys of arthritic rats.