Possible mechanisms for the differential effects of high linoleate safflower oil and high α-linolenate perilla oil diets on platelet-activating factor production by rat polymorphonuclear leukocytes

As compared with high dietary linoleate safflower oil, high dietary α-linolenate perilla oil decreased platelet-activating factor (PAF) production by nearly half in calcium ionophore (CaI)-stimulated rat polymorphonuclear leukocytes (PMN). In the CaI-stimulated PMN from the perilla oil group, the accumulated amount of arachidonate (AA) plus eicosapentaenoate (EPA) was 30% less and that of lyso-PAF was 50% less, indicating that the decreased availability of lyso-PAF is a factor contributing to the relatively low PAF production. Consistently, eicosatetraynoic acid (ETYA), a dual inhibitor of cyclooxygenase and lipoxygenase, increased free fatty acids (FFA) and decreased PAF production possibly by decreasing the availability of lyso-PAF. Although, leukotrienes (LTs) have been proposed to stimulate PAF production synergistically, a potent LTB₄ receptor antagonist, ONO-4057, decreased the formation of free fatty acids and LTB₄, but stimulated PAF production somewhat, indicating that LTB₄ may not stimulate PAF production in PMN. Lysophospholipid-induced transacylase (CoA-independent transacylase) activity in PMN homogenates was 25∼30% lower in the perilla oil group but no significant differences were observed in the lyso-PAF acetyltransferase and PAF acetylhydrolase activities between the two dietary groups. Thus, decreased transacylase activity is another factor associated with the relatively low PAF production in the perilla oil group.