Effects of ovarian steroids on the 17 alpha-hydroxylase activity toward progesterone in a human ovarian follicle at the late follicular phase.

The dominant follicle at the late follicular phase was obtained from a human ovary, the follicular wall was homogenized and centrifuged at 800 g. Then, the supernatant fluid was incubated with [14C]-progesterone and the radioactive products were quantitated. 17-Hydroxyprogesterone, 16 alpha-hydroxyprogesterone and androstenedione were identified under the present experimental conditions. The apparent KM value of the 17 alpha-hydroxylase toward progesterone was 0.19 +/- 0.01 microM. Various ovarian steroids (17-hydroxyprogesterone, 20 alpha-hydroxy-4-pregnen-3-one. 16 alpha-hydroxyprogesterone, androstenedione, testosterone, estrone and estradiol-17 beta) were tested for their effects on this hydroxylase activity. Among them, 20 alpha-hydroxy-4-pregnen-3-one and 17-hydroxyprogesterone inhibited on the enzyme activity, significantly. They acted competitively and their Ki values were 0.23 microM for 20 alpha-hydroxy-4-pregnen-3-one and 0.54 microM for 17-hydroxyprogesterone.