Purification of rat testicular microsomal 17-ketosteroid reductase. Evidence that 17-ketosteroid reductase and 17 beta-hydroxysteroid dehydrogenase are distinct enzymes

17 beta-Oxidation of estradiol and testosterone in the human testis

The oxidation of 17 beta-estradiol in the human testis was studied in order to characterize a potentially important regulatory step in the action of estradiol in the human testis. 17 beta-Estradiol was shown to be converted to estrone, a weaker estrogen, in a reaction which was not inhibited by testosterone to any greater extent. When compared with the corresponding 17 beta-oxidation of testosterone, differences in coenzyme preferences, hydrogen ion sensitivity and inhibitions by estradiol and testosterone were observed, suggesting to a presence of different 17 beta-hydroxysteroid dehydrogenases in the human testis. Thus the human testis may counteract some of the deleterious effects of 17 beta-estradiol on androgen biosynthesis by metabolizing it to a weaker estrogen, in a reaction which probably is not inhibited by high testicular testosterone concentrations.

Steroid 17 alpha-hydroxylase activity of ovarian granulosa cells from hypophysectomized immature rats treated with pregnant mare's serum gonadotropin (PMS)

Immature hypophysectomized rats were injected with 2mg of diethylstilbestrol to increase granulosa cell numbers and with 20 IU of PMS to stimulate ovarian growth. Steroid 17 alpha-hydroxylase activity of cultured granulosa cell, harvested from mature follicles 48 h after injection of PMS, was demonstrated using a tritium exchange assay with 17 alpha 3H-pregneneolone as substrate. For comparison, aromatase activity of the same cells was examined by a similar assay using 1 beta 3H-testosterone as the substrate. The activities of the two enzymes were similar when expressed in terms of the amount of substrate converted per unit time. While an NADPH generating system in the incubation medium was essential for demonstrating any hydroxylase activity, 10-15% of the total aromatase activity could be found without added cofactor. Attempts to alter hydroxylase activity of granulosa cells by inclusion of LH, FSH or prolactin in the incubation medium were unsuccessful. However, activity could be change by prostaglandins (PG) or agents which can alter PG synthesis. Activity was increased by low concentrations of phospholipase A2 (PLA2), histamine, and arachidonic acid (AA). Large doses of PLA2, or AA, were inhibitory. PGE2, but not PGF2 alpha, increased, while indomethacin decreased, hydroxylase activity. The results clearly indicate that granulosa cells in the rat have a potent 17-hydroxylase system and therefore do not support the widely held contention that lack of this enzyme is one of the bases for the need for two kinds of cells for ovarian estrogen production.