The human corpus luteum secretes 5 alpha-pregnane-3,20-dione

A radioimmunoassay for 5 alpha-pregnane-3,20-dione (5 alpha-DHP) in plasma is described. The concentration of 5 alpha-DHP in peripheral plasma during the follicular phase of the menstrual cycle was of the same order of magnitude as that of progesterone (P). During the luteal phase, the plasma 5 alpha-DHP was 8-fold higher than in the follicular phase and about 1/3 of the P concentration. The concentration of 5 alpha-DHP in ovarian venous plasma draining an ovary containing the corpus luteum was 22-fold higher than the concentration in plasma from the contralateral ovarian vein. These results show that the corpus luteum secretes significant amounts of 5 alpha-DHP.