Production of 17-hydroxypregnenolone and 17-hydroxyprogesterone by the immature rat ovary

Evidence that immature rat liver is capable of participating in steroidogenesis by expressing 17alpha-hydroxylase/17,20-lyase P450c17

Steroid hydroxylase cytochrome P450c17 has been previously purified from microsomal fractions of immature rat livers. In this study, we investigated the expression of P450c17 in rat livers to understand a role of steroidogenesis in the extrasteroidogenic tissue. Upon immunoblot analysis utilizing liver microsomes from rats, P450c17 was detected in 1 and 3 week old rats but not in adult rats. Data from immunohistochemical studies also showed a similar age-dependent expression of P450c17 and indicated that P450c17 detected in immature rat livers is localized in cells surrounding interlobular veins. This age-dependent expression of P450c17 in rat livers was observed in both sexes. Upon enzymatic analysis utilizing microsomal fractions from livers, levels of 17alpha-hydroxylase and 17,20-lyase activity for pregnenolone and progesterone increased by 3 weeks and dramatically reduced at 7 weeks, which is consistent with the expression level of P450c17. These data clearly indicate that P450c17 is expressed in immature rat liver to produce 17alpha-hydroxysteroids and C19-steroids. Based upon immunoblot analysis, the expression level of P450c17 in immature rat livers was approximately one third of that in testis. Compared expression level of P450c17 and total volume of organs between liver and testis, the total amount of steroid metabolites produced by liver P450c17 could be greater than that produced by gonadal P450c17. Because of the absence of P450c17 in rat adrenal glands, rat liver could be the major site for producing 17alpha-hydroxysteroids and C19-steroids in this particular period of life. Although physiological products formed by P450c17 in liver and their roles remain to be elucidated, this study suggests a large capacity of prepubertal rat liver for participating the production of steroid hormones and a putative importance of 17alpha-hydroxysteroids and C19-steroids, such as cortisol and androstendione, which are generally believed to be minor components of steroid hormones in rodents.

Conversion of 17 alpha-hydroxyprogesterone to 5 alpha, 3 alpha, and 20 alpha-reduced metabolites by female rat anterior pituitary and hypothalamus

The metabolism of 17 alpha-[3H]hydroxyprogesterone was examined in female rat anterior pituitary and hypothalamic tissues. After reverse isotopic dilution analysis and purification to constant specific activity, the following 5 alpha-, 3 alpha- and 20 alpha-reduced products were detected in both tissues: 17 alpha-hydroxy-5 alpha-pregnane-3,20-dione; 3 alpha,17 alpha-dihydroxy-5 alpha-pregnan-20-one; 17 alpha,20 alpha-dihydroxy-4-pregnen-3-one and 5 alpha-pregnane-3 alpha,17 alpha,20 alpha-triol. While the metabolites formed were qualitatively the same, there were quantitative differences between the two tissues. The 3 alpha,5 alpha-reduced metabolite, 3 alpha,17 alpha-dihydroxy-5 alpha-pregnan-20-one, was the principal product in the anterior pituitary while the 5 alpha-reduced metabolite, 17 alpha-hydroxy-5 alpha-pregnane-3,20-dione, was produced in largest amount by the hypothalamus. With both tissues, the aforementioned four products plus starting substrate accounted for nearly all of the starting radioactivity. There was no evidence for the formation of C19 steroids (androgens) despite the presence of the 17 alpha-hydroxy group.

Relationship between in vivo and in vitro 17 alpha-hydroxylase and C17,20-lyase activity in ovaries of immature hypophysectomized rats treated chronically with human chorionic gonadotropin

The production of 3H2O from 17 alpha-3H-progesterone and 14CH3COOH from [21-14C]progesterone were used to measure the 17 alpha-hydroxylase and C17,20-lyase activities respectively in the microsomal + mitochondrial fraction of homogenates of ovaries from immature hypophysectomized rats chronically treated with human chorionic gonadotropin (hCG). The highly stimulated thecal and interstitial tissues were considered the only source of enzyme. hCG produced an increase in 17-hydroxyprogesterone, and androstenedione, but a drastic decrease in enzyme activity within 6 h; this could be largely prevented by pretreatment of the rats with cycloheximide or aminoglutethimide but actinomycin D was ineffective. After a nadir at 24 h, enzyme activities increased to more than double those of the starting level; this could be prevented by cycloheximide. Maximal activity levels were greatly decreased by cycloheximide and modestly increased by aminoglutethimide. Cessation of treatment at 60 h followed by a single injection of hCG 24 h later did not cause a loss, but delays of 36 or more hours produced a dramatic decrease in enzyme activity, which could be prevented by aminoglutethimide. The results indicate that the level of activity of these enzymes attained in the ovary following exposure to hCG is determined by a balance between the amount of substrate provided and production of enzyme and/or stimulating factors. Therefore, maintenance of increased enzyme activity induced by gonadotropin appears to be under genomic control.

The C17,20-lyase, 17 alpha-hydroxylase and aromatase activity in rat ovarian granulosa cells stimulated in vivo by gonadotropins

Immature hypophysectomized rats were injected with PMS; some groups received hCG 48h later. The C17,20-lyase activity in the granulosa cells removed from the large preovulatory follicles was estimated by the amount of labelled acetic acid produced from 21 (14C) progesterone or 17-hydroxyprogesterone. 17 alpha-hydroxylase and aromatase activity were measured by the tritium exchange method. Although the granulosa cells contained lyase, it was considerably less than their hydroxylase activity. The remaining tissue, consisting of small follicles and hypertrophied thecal and interstitial tissue, had a great deal more lyase and hydroxylase activity than did the granulosa cells. The results are consistent with the view that granulosa cells can produce estrogen from progesterone and do not require androgen precursors from the theca and/or interstitium.