Evidence for a Decrease in Aromatase Activity in the Ovarian Granulosa Cells of Amago Salmon (Oncorhynchus rhodurus) Associated with Final Oocyte Maturation

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Abstract
Aromatase activity in the isolated granulosa layers of amago salmon (Oncorhynchus rhodurus) ovarian follicles was examined during the course of vitellogenesis and final oocyte maturation and ovulation. Estradiol-17β production by isolated granulosa layers incubated with exogenous testosterone increased during the period of vitellogenesis to reach a peak in late vitellogenesis, and then declined rapidly, in association with the ability of the oocyte to mature in response to partially purified salmon gonadotropin (SG-G100). Extremely low levels of estradiol-17β were produced by granulosa layers from follicles which had undergone final oocyte maturation in vivo and by post-ovulatory follicles. SG-G100 had no discernible effect on estradiol-17β production. These results are discussed in relation to other studies on the endocrine control of steroidogenesis in this species.

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