Effects of estradiol and progesterone on platelet calcium responses

We investigated the effects of 17 beta-estradiol (beta E2), alpha-estradiol (alpha E2), and progesterone (P) on baseline and vasopressin (AVP)-induced [Ca2+]i in human platelets obtained from healthy male and female volunteers. Platelets were treated with beta E2, alpha E2, P, or ethanol vehicle for 30 min at 37 degrees C. In males, both beta E2 and P at 10(-5) mol/L reduced the AVP-induced rise in [Ca2+]i, to 72 +/- 3% (mean +/- SEM) and 53 +/- 3%, respectively. However, at 10(-6) mol/L only beta E2 had a significant effect (P < .02). In females, 10(-6) and 10(-5) beta E2 reduced the AVP response to 85.3 +/- 4.6% and 80.8 +/- 5.4% of control values, respectively. Progesterone (10(-6) and 10(-5) mol/L) reduced the AVP response to 83.8 +/- 5.1% and 60.3 +/- 2.0% of control values, respectively. The inactive estrogen alpha E2 had no effect on basal or AVP-induced rise in [Ca2+]i in either subject population, suggesting hormonal specificity. Neither beta E2 nor P affected baseline [Ca2+]i in either population. Thus, by attenuating [Ca2+]i responses in platelets, beta E2 and P may modulate platelet aggregation and atherosclerosis.