Inhibition of Platelet Aggregation and Reduction of Gpiib/Iiia Receptor by Progesterone

Abstract

Several studies have suggested that hormone replacement therapy (HRT) may

attenuates the increased risk of cardiovascular disease in postmenopausal woman. The

effects of progestin in the combined HRT is widely used to attenuate the endometrialcancerogenic effect of estrogen. However the effects of progesterone on the

atherogenic process have not been understood. In the preliminary study, in vitro

effects of progesterone (P) and medroxyprogesterone acetate (MPA) on ADP-and

collagen-induced-platelet aggregation were examined using impedance aggregometry.

As well as the quantification of the expression of CD41 antigen, a marker of platelet

GP IIb-Illa receptor which play a critical role for platelet aggregation and

pathogenesis of atherosclerosis. Preincubation of citrated whole blood from Thai male

healthy volunteers 3 minutes with P(1-1000 nM) or MPA (1-1000 nM) caused a

concentration-dependent inhibition of ADP (50uM) and collagen (0.3mg/ml) induce-platelet

aggregation. Furthermore P and MPA also reduced CD41 expression in dose-dependent

manner, assessed by using a single-color FACS cell analysis. These results

suggesting that the reduction of GP Ilb/Illa receptor expression by P and MP A may

contributed, in part, to its anti-aggregatory effect and that its anti-aggregatory effect

might be one of the factors involved in the decrease of the incidence of atherosclerotic

cardiovascular disease in postmenopausal HRT.