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  • Title: 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.
    Author: Johnson DC, Griswold T.
    Journal: J Steroid Biochem; 1986 Feb; 24(2):637-43. PubMed ID: 3486324.
    Abstract:
    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.
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