Although platelet-activating factor (PAF) is a well-known mediator in experimental shock, its precise role in acute renal failure remains to be defined. Male Wistar rats (209 +/- 12 g) were placed in individual metabolic cages for 24 h before i.v. injection of PAF (2-6 micrograms/kg). Injection of 6 micrograms/kg PAF proved lethal and use of such a high dose was thus discontinued. Administration of 2 micrograms/kg and 4 micrograms/kg PAF resulted in a fall of glomerular filtration rate (GFR) associated with a reduction in urinary flow rate (UFR). Rats pretreated with BN 52021 (25 mg/kg p.o.) exhibited values of GFR similar to that of the control group, but not after 4 micrograms/kg PAF. In addition, in the group of BN 52021 pretreated rats and injected with 2 micrograms/kg or 4 micrograms/kg PAF, UFR was not significantly different from that of the control group at 24 h. Examination by electron microscopy revealed the presence of platelets in the glomeruli, as well as loss of fixed anionic charges in PAF injected rats. The presence of these platelets was not observed in rats treated with BN 52021 and injected with PAF. No changes in GFR and UFR were observed at 6 h or 24 h in vehicle or BN 52021 treated rats. Thus, BN 52021 which affords protection against acute renal failure induced by PAF may be of therapeutic value in other types of kidney disease in which this mediator is active.