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Departments of Surgery, and Physiology and Biophysics, Mayo Clinic and Foundation, Rochester, Minnesota 55905
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 F2
, platelets (25,000 platelets/µl)
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
endothelium-dependent 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.
estrogen; venous thrombosis
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