Plasma and platelet lipid composition and platelet aggregation by arachidonic acid in women on the pill.

Sensitivity to induction of platelet aggregation by arachidonic acid (AA) and changes in plasma and platelet polyunsaturated fatty acid distribution were studied in seven women before and after six months of oral contraceptive (OC) treatment with a combination of d-norgestrel (0.25 mg) and ethinylestradiol (0.05 mg). Special interest was focused on AA because certain metabolites of fatty acid induce platelets to aggregate and are considered to play a crucial role in thromboembolic processes. In plasma, AA concentrations increased slightly, but significantly, in both the free fatty acid (FFA) and phospholipid fractions; in platelets AA increased in the phospholipid and neutral lipid fractions. The threshold aggregating concentration (TAC) of AA was significantly reduced in platelets of women after six months of OC treatment (0.65 +/- 0.08 versus 0.30 +/- 0.04 mM). This suggests that changes in platelet fatty acid composition may be associated with in vitro changes in platelet sensitivity to AA. Such changes may contribute to the thrombotic tendency associated with OC treatment.