Summary. Rainbow trout testicular fragments were incubated at 8 different stages of the spermatogenetic cycle in the presence of tritiated progesterone or 17a-hydroxyprogesterone. This paper describes the potential enzymatic activities involved in the At route leading to the production of « major » derivatives. 1) A 5-reductase converted progesterone into 5Cï(!)-pregnane-3,20-dione. 2) A 20a-oxydoreductase converted 17a-hydroxyprogesterone into 17a-hydroxy-20/3-dihydroprogesterone. At some stages this synthesis reached or exceeded androgen production.3) 20¡J-oxydoreductase, 17-20 desmolase and 17j8-oxydoreductase are proposed as putative enzymatic steps in the regulation and modulation of steroidogenic metabolism in the trout testis.4) The physiological role of the different major steroids synthesized by the testis in vitro is discussed, and the hypothesis of the involvement of 17a-hydroxy-20¡J-dihydroprogesterone in the control of germ cell mitotic activity and/or feedback on the hypothalamo-pituitarv system is examined.Introduction.
Summary. Aromatase activity has been studied in the rainbow trout ovary in a perifusion system. During early vitellogenesis, as in other stages of the annual cycle, the ovaries were capable of aromatizing androstenedione and testosterone. Aromatase activity increased from the postovulatory stages to exogenous vitellogenesis.When highly purified salmon glycoprotein maturational gonadotropin was added to the medium (50 ng/ml), the androstenedione/testosterone ratio was reduced by half. This indicates a stimulation of 17p-hydroxysteroid dehydrogenase activity favourizing the formation of testosterone. At a concentration of 50, 150 or 300 ng/ml, the gonadotropin inhibited between 13 and 38 p. 100 of the aromatase enzymatic activity.Introduction.
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