Pharmacological profiles of a novel specific platelet activating factor (PAF) antagonist, TCV-309 (3-bromo-5-[N-phenyl-N-[2-[2- (1,2,3,4-tetrahydro-2-isoquinolycarbonyloxy)ethyl] carbamoyl]ethyl] carbamoyl]-1-propylpyridinium nitrate] and its beneficial effects in shock were examined. TCV-309 specifically inhibited PAF-induced aggregation of rabbit and human platelets, and [3H]PAF binding to rabbit platelet microsomes with IC50 values of 33, 58 and 27 nM, respectively. It was as potent as WEB 2086 and more potent than CV-6209 and CV-3988. TCV-309 did not cause hemolysis in human or rat blood due to a detergent-like action. In rats, TCV-309 selectively inhibited the PAF-induced hypotension, hemoconcentration and death with ED50 values of 2.7, 6.4 and 1.7 micrograms/kg (i.v.), respectively. TCV-309 most potently protected mice from death induced by PAF and due to anaphylactic shock with ED50 values of 2.1 and 2.6 micrograms/kg (i.v.), respectively, when compared with CV-3988, CV-6209, WEB 2086 (i.v.) and L-652731 (p.o.). TCV-309 also reversed PAF-induced hypotension and endotoxin-induced hypotension in rats with ED50 values of 3.3 and 1.2 micrograms/kg (i.v.), respectively. There was a significant linear relationship between the ability (ED50 value) of these PAF antagonists to prevent death induced by PAF and death due to anaphylactic shock in mice, and between their reversing ability (ED50 value) for the hypotension induced by PAF and endotoxin in rats. TCV-309 (100 micrograms/kg i.v.) protected rats from death induced by endotoxin. Thus, PAF may be a lethal mediator in anaphylactic shock and a hypotensive mediator in endotoxin shock in rodents.