Platelet-activating factor (PAF) may contribute to the renal functional impairment of endotoxemia. We therefore examined 1) the effects of two specific PAF-receptor antagonists, L-653,150 and L-652,731, on endotoxin-induced acute renal insufficiency and 2) the renal hemodynamic actions of PAF in anesthetized postpartum Wistar rats. An intravenous injection of endotoxin at 150 micrograms/kg reduced glomerular filtration rate (GFR), renal plasma flow (RPF), and filtration fraction (FF) without a change in mean arterial pressure. L-653,150, 50 mg/kg orally, attenuated the endotoxin-induced fall in GFR, RPF, and FF. An intravenous injection of L-652,731, 0.3 mg/kg, followed by an infusion at 16 micrograms.kg-1. min-1 prevented the endotoxin-elicited reduction in GFR, RPF, and FF. L-652,731 also reversed the endotoxin-induced renal functional impairment. PAF, infused at 16 ng.kg-1.min-1 into the suprarenal aorta, reduced GFR, RPF, and FF without a significant change in renal arterial pressure. L-652,731 prevented the PAF-induced changes. In contrast, meclofenamate worsened the renal hemodynamic effects of PAF. We conclude that PAF may play an important role in mediating the endotoxin-induced acute hemodynamic renal insufficiency in rats with normotensive endotoxemia.