Formation of steroids by the pregnant mare. IV. Metabolism of 14 C-mevalonic acid and 3 H-dehydroisoandrosterone injected into the fetal circulation.

Abstract

A mixture of 2-14C-mevalonic acid and 3H—dehydroisoandrosterone was injected into the umbilical circulation of a horse fetus following which the maternal urine was collected for 3 days. Steroid conjugates present in urine were hydrolyzed and separated into neutral and phenolic fractions. From the phenolic fraction estrone, 17aestradiol, equilin and equilenin were isolated. Only the classical estrogens estrone and 17α—estradiol contained both 3H and 14C, while the ring B unsaturated estrogens contained only 14C. From the neutral fraction 14C—labeled 3β—hydroxy-5α—pregnan- 20-one, 5α—pregnane-3β,20β—diol, and 5β—pregnane- 3(3,20α—diol were isolated. These results demonstrate that the route of biosynthesis of both the classical estrogens and the ring B unsaturated estrogens is the same up to the stage of mevalonic acid. Thus the bifurcation in the classical pathway of estrogen biosynthesis reported previously by us is occurring at a point after the formation of mevalonic acid and prior to the formation of squalene. (Endocrinology92: 1397, 1973)