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RESEARCH PRODUCT

The effect of hormone replacement therapy on Ca2+ mobilization and P-selectin (CD62P) expression in platelets examined under flow cytometry.

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A series of events, such as increase of cytoplasmic free calcium (Ca 2+ ) and expression of P-selectin (CD62P), an adhesion molecule, on the platelet surface, are significant indicators of platelet activation. We have used flow cytometry to examine Ca 2+ mobilization and CD62P expression in platelets in whole blood obtained in women prior to, and after, different forms of hormone replacement therapy. Thirty-two women completed a protocol consisting of two consecutive 1-month periods under oestradlol (E 2 ), administered orally (2 mg/day) or transdermally (50 μg/day) in random order, followed by a 4-week transdermal sequential regime, in which, during the last 14 days, either progesterone (300 mg/day) or medroxyprogesterone acetate (5 mg/day) was added to the 50 μg/day E 2 , administered orally in random order. None of the hormonal combinations determined significant changes in Ca 2+ mobilization or CD62P expression in non-stimulated platelets. However, stimulation of platelets with adenosine diphosphate, but not with thrombin, caused a significant increase in cytoplasmic Ca 2+ concentration during treatment with transdermal E 2 plus progesterone. Also when stimulating with thrombin, transdermal E 2 was more active than oral E 2 in increasing CD62P expression, a difference that was not reduced by the addition of progestogens. In conclusion, hormone replacement therapy only increased Ca 2+ mobilization or CD62P expression in stimulated platelets, and then followed a varied pattern that was dependent on the stimulant and on the specific hormonal formulation.