Regulation of prostacyclin and thromboxane production by human umbilical vessels: the effect of estradiol and progesterone in a superfusion model.

To study the production of the vasodilatory prostacyclin (PGI2) and vasoconstrictory thromboxane A2 (TxA2) by the human umbilical vessels, vascular segments collected from the cords of healthy newborns (n = 15) after normal pregnancies were superfused with Eagle's medium at 37 degrees C under continuous oxygenation. The stable metabolites of PGI2 and TxA2, 6-keto-prostaglandin F1 alpha and thromboxane B2 (TxB2) respectively, were measured from the superfusates with radioimmunoassays. All vascular segments studied produced 6-keto-PGF1 alpha and TxB2 without any significant difference between the arteries and veins. 6-keto-PGF1 alpha was produced some 10-15 times more than TxB2. 17-beta-estradiol at concentrations of 10, 100 and 1000 ng/ml dose-dependently stimulated the 6-keto-PGF1 alpha formation, but had no effect on TxB2 generation. Progesterone 50, 500 and 5000 ng/ml caused no changes in 6-keto-PGF1 alpha or TxB2 generations but even the smallest concentration of progesterone abolished the stimulating effect of estradiol. These results thus suggest that the high circulating levels of 17-beta-estradiol and progesterone in the umbilical vessels may be important in the regulation of PGI2 synthesis in the umbilical vessels in vivo.