Genome and Hormones: Gender Differences in Physiology Selected Contribution: Effects of sex and ovariectomy on responses to platelets in porcine femoral veins

Lewis, D. A., M. P. Bracamonte, K. S. Rud, and V. M. Miller. Selected Contribution: Effects of sex and ovariectomy on responses to platelets in porcine femoral veins. J Appl Physiol 91: 2823–2830, 2001.—Estrogen replacement increases risk of venous thrombosis. In this study, we determined responses in vitro to platelets and platelet products in veins from adult male and intact and ovariectomized female pigs. When contracted with prostaglandin F2a, platelets (25,000 platelets/ml) caused relaxation in veins with endothelium. Higher numbers of platelets caused contraction in veins with and without endothelium. In veins without endothelium, contractions were greater in veins from male than in veins from female pigs, and contractions in intact female pig veins were greater than in ovariectomized females pig veins. Platelet products 5-hydroxytryptamine and thromboxane (analog U-46619) caused comparable contractions in all veins; contractions to prostacyclin were less in veins from intact female pigs. ADP caused comparable endotheliumdependent relaxations in all groups. These relaxations were increased by indomethacin in veins from intact males and females; with inhibition of nitric oxide, relaxations were comparable in all groups. These results suggest that venous responses to platelets vary with sex and presence of ovaries in female pigs. These variations reflect differences in type and quantity of substances released from platelets as well as the sensitivity of the smooth muscle to some vasoactive substances. In addition, products of cyclooxygenase may reduce endothelium-dependent relaxations in veins.