Alteration of platelet responses to metabolites of arachidonic acid by oral contraceptives.

The effects of oral contraceptive (OC) usage on platelet responsiveness to arachidonic acid metabolites was investigated. Platelets obtained from women who had been taking oral contraceptives for at least 3 months were compared with those of age-matched controls. Both the basal and prostacyclin (PGI2)-stimulated platelet cAMP levels were significantly lower in OC users than in non-users. There was no significant difference in the PGD2-stimulated cAMP levels between the two groups. Furthermore, platelet aggregability to U46619, a TXA2 agonist, was greatly enhanced by OCs. Our data suggests that OC usage can specifically enhance platelet responsiveness to TXA2 while suppressing platelet responsiveness to PGI2. Thus their overall effect would be a disruption of normal platelet responses in favour of thrombus formation.