Effects of estradiol and progesterone on platelet calcium responses

We investigated the effects of 17β-estradiol (βE₂), α-estradiol (αE₂), 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 βE₂, αE₂, P, or ethanol vehicle for 30 min at 37°C. In males, both βE₂ and P at 10^-5mol/L reduced the AVPinduced rise in [Ca²⁺]_i, to 72 ± 3% (mean ± SEM) and 53 ± 3%, respectively. However, at 10^-6 mol/L only βE₂ had a significant effect (P < .02). In females, 10^-6 and 10^-5 βE₂ 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 αE₂ had no effect on basal or AVP-induced rise in [Ca²⁺]_i in either subject population, suggesting hormonal specificity. Neither βE₂ nor P affected baseline [Ca²⁺]_i in either population. Thus, by attenuating [Ca²⁺]_i responses in platelets, βE₂ and P may modulate platelet aggregation and atherosclerosis.