Sex difference in platelet aggregation detected by new aggregometry using light scattering

Earlier studies in platelet aggregation have shown that females seemed to h ave greater aggregability than males as detected by conventional aggregomet ry which used light transmission (LT), but controversy still remains. This study was performed to determine whether sex difference exists in platelet aggregation by using the recently developed laser light scattering (LS) met hod, which can detect small aggregates (i.e., two or three platelets). Bloo d was drawn from healthy volunteers (10 male and 10 female in follicular ph ase after menstruation), and platelet aggregation was detected by either LT or LS method in platelet rich plasma. Platelet aggregation was stimulated by increasing concentration of adenosine 5'-diphosphate (ADP, 0, 0.5, 1 and 2 muM). To detect the effect of sex hormones, platelets were incubated wit h estradiol (10 nM) or testosterone (40 nM) for 30 min, then platelet aggre gation studies were performed. LT method revealed that female had greater a ggregability than male. With weak stimuli (less than or equal to 1 muM ADP) , LS method showed that females had more medium aggregates than males, and that testosterone decreased small aggregates, and that estradiol decreased all sizes of aggregates. These data suggest that the female is more conduct ive to platelet aggregation than the male at a physiologic concentration of ADP (less than or equal to 1 muM), but that both estradiol (10 nM) and tes tosterone (40 nM) have countereffects on platelet aggregation at the same c ondition. Therefore, the reason why females have greater aggregability than males may partly be explained by their lack of testosterone, but the mecha nism still remains to be elucidated.