Aggregation, release and desensitization induced in platelets from five species by platelet activating factor (PAF).

PAF-induced aggregation and dense granule release (ATP release) were investigated in human, primate, guinea pig, rabbit and rat platelet-rich plasma (PRP). Guinea pig PRP was most sensitive to PAF, followed by rabbit and then human. PRP from rats and primates did not aggregate or release when exposed to PAF. In guinea pig and rabbit PRP, release was independent of aggregatory response. In human PRP high doses of PAF (5 X 10(-7) M) caused maximum aggregation and a biphasic ATP release, whilst lower concentrations (3 X 10(-8) M) induced biphasic aggregation and one phase of ATP release concomitant with the second phase of aggregation. Aggregation and ATP release induced by PAF in guinea pig and rabbit PRP is dependent upon Ca++ levels, whilst the response of human platelets is relatively independent of the Ca++ level above a certain threshold concentration. The PRP from the three species which aggregated with PAF also demonstrate the phenomenon of desensitization.