Tumor necrosis factor-alpha (TNF-alpha) has been implicated in the pathogenesis of hypertension and renal injury. However, the direct effects of TNF-alpha on renal hemodynamic and excretory function are not yet clearly defined. We examined the renal responses to infusion of TNF-alpha (0.33 ng.g(-1).min(-1)) in anesthetized mice. Renal blood flow (RBF) and glomerular filtration rate (GFR) were determined by PAH and inulin clearance. The urine was collected from a cannula inserted into the bladder. Following the 60-min control clearance period, TNF-alpha infusion was initiated and 15 min were given for stabilization followed by another 60-min clearance period. TNF-alpha alone (n = 7) caused decreases in RBF (7.9 +/- 0.3 to 6.4 +/- 0.3 ml.min(-1).g(-1)) and GFR (1.04 +/- 0.06 to 0.62 +/- 0.08 ml.min(-1).g(-1)) as well as increases in absolute (0.8 +/- 0.3 to 1.4 +/- 0.3 micromol.min(-1).g(-1)) and fractional excretion of sodium (0.5 +/- 0.2 to 1.5 +/- 0.4%) without affecting arterial pressure. TNF-alpha also increased 8-isoprostane excretion (8.10 +/- 1.09 to 11.13 +/- 1.34 pg.min(-1).g(-1)). Pretreatment with TNF-alpha blocker etanercept (5 mg/kg sc; 24 and 3 h before TNF-alpha infusion; n = 6) abolished these responses. However, TNF-alpha induced an increase in RBF and caused attenuation of the GFR reduction in mice pretreated with superoxide (O(2)(-)) scavenger tempol (2 microg.g(-1).min(-1); n = 6). Pretreatment with nitric oxide (NO) synthase inhibitor nitro-l-arginine methyl ester (0.1 microg.g(-1).min(-1); n = 6) resulted in further enhancement in vasoconstriction while natriuresis remained unaffected in response to TNF-alpha. These data suggest that TNF-alpha induces renal vasoconstriction and hypofiltration via enhancing the activity of O(2)(-) and thus reducing the activity of NO. The natriuretic response to TNF-alpha is related to its direct effects on tubular sodium reabsorption.