The influence of age, sex, and the use of oral contraceptives on the inhibitory effects of endothelial cells and PGI2 (prostacyclin) on platelet function.

The inhibitory effects of human endothelial cells (ECM) and PGI2 (prostacyclin) on platelet function have been examined in 60 healthy subjects. 5 groups were studied. I. 10 women (19-33 yrs.); II. 10 women (21-31 yrs.) using combined oral contraceptives; III. 10 postmenopausal women (45-66 yrs.); IV. 20 men (24-48 yrs.) and V. 10 men (48-71 yrs.). Spontaneous platelet aggregation in platelet-rich plasma (PRP) was commonly observed in groups II, III, and V. This was prevented when PRP was incubated with ECM, aspirin (ASA), or PGI2. ADP-induced platelet aggregation (PA) was always reduced by ECM, but significantly less in groups II and III. Collagen-induced PA was inhibited by ECM, but less in groups I, II, III and V than in young men (IV). ECM significantly reduced collagen-induced prostaglandin (MDA) production in platelets. Again, the inhibitory effect was significantly reduced in groups II and III. Platelet factor 3 activity, measured after exposure of PRP to ADP, was significantly reduced by ECM, but was significantly less in groups II, III, and V than in group I. Less of an inhibitory, effect of PGI2 upon ADP-induced PA was shown by all groups of females than by the two groups of males.