STRUCTURE-ACTIVITY-RELATIONSHIPS FOR PLATELET-ACTIVATING-FACTOR (PAF) AND ANALOGS REVEAL DIFFERENCES BETWEEN PAF RECEPTORS ON PLATELETS AND MACROPHAGES

Analogues of PAF were examined for their potency in stimulating either platelet aggregation or macrophage superoxide anion generation. Modification of either the alkyl side-chain or the acetyl side-chain increased the relative potency of PAF analogues in macrophages, but all these compounds were more active in platelets. However, an analogue of PAF with an increased inter-ionic distance in the polar head group, hexanolamine PAF, showed a greater potency in macrophages than platelets. The latter compound also appeared to act as a partial agonist in both rabbit platelets and guinea-pig macrophages, but not in guinea-pig platelets. Differences in the rank order of potency of the PAF analogues in stimulating these cell elements suggest that platelet and macrophage PAF receptors differ.