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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.
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