Characteristics of estrogen-2/4-hydroxylase of porcine ovarian follicles: influence of steroidal and non-steroidal agents on the activity of the enzyme in vitro.
The conversion of [3H]estradiol to 2-hydroxyestradiol (2-OH-E2) by homogenates of porcine ovarian follicles was assayed in vitro in the presence and absence of 10 and 100 microM concentrations of the following potential substrates or inhibitors of estrogen-2/4-hydroxylase (E-2/4-H): (1) estrogens; estrone (E1), estriol (E3) and 17 alpha-estradiol (17 alpha-E2), (2) catecholestrogens; 2-hydroxyestradiol (2-OH-E2), 4-hydroxyestradiol (4-OH-E2) and 2-hydroxyestrone (2-OH-E1); (3) 2-methoxyestradiol (2-MeO-E2); (4) halogenated estrogens; 2-bromoestradiol, (2-Bromo-E2) 4-bromoestradiol and 2,4-dibromoestradiol; (5) androgens; testosterone (T), dihydrotestosterone (DHT) and androstenedione; (6) progesterone; (7) epinephrine; (8) inhibitors of steroid aromatase; aminoglutethimide and 4-hydroxyandrostenedione and (9) SKF 525A, an inhibitor of cytochrome P-450. Progesterone and 2-Bromo-E2 were the two most effective inhibitors (2-OH-E2 formation = 4 and 5% of control at 100 microM and 29.6 and 17.4% at 10 microM of progesterone and 2-Bromo-E2, respectively). 2-MeO-E2 at 100 microM was nearly as effective as progesterone in inhibiting E-2/4-H activity but only caused about 50% inhibition at 10 microM. The three catecholestrogens reduced 2-OH-E2 formation to about the same degree (21-23% of control at 100 microM). The 2,4-dibromo-E2 was equipotent with the catecholestrogens while 4-bromo-E2 was about half as effective. The phenolic estrogens, potential substrates for the enzyme, reduced 2-OH-E2 formation to different degrees, with E3 being the most effective. Among the androgens, DHT was almost as effective an inhibitor as the catecholestrogens, T was about half as effective while androstenedione had no effect. Epinephrine and the two inhibitors of aromatase did not inhibit E-2/4-H activity. SKF 525A inhibited E-2/4-H activity but with a potency only about 1/10th that reported for liver.
D000077584:2-Methoxyestradiol; D000818:Animals; D002395:Catecholamines / Q000494:pharmacology; D002396:Catechols / Q000494:pharmacology; D019363:Cytochrome P-450 CYP1A1; D004958:Estradiol / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D004967:Estrogens / Q000494:pharmacology; D004970:Estrone / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D010053:Ovary / Q000187:drug effects / Q000201:enzymology*; D011335:Proadifen / Q000494:pharmacology; D011374:Progesterone / Q000494:pharmacology; D013250:Steroid Hydroxylases / Q000378:metabolism*; D013552:Swine
D002395:Catecholamines; D002396:Catechols; D004967:Estrogens; D004970:Estrone; D011374:Progesterone; D004958:Estradiol; D000077584:2-Methoxyestradiol; D011335:Proadifen; D013250:Steroid Hydroxylases; D019363:Cytochrome P-450 CYP1A1; C020120:estrogen 2-hydroxylase