Interralation between various hormones for egg production in birds

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Domestic birds are an ideal experimental model for the study of the inter-action of the granulosa and theca cells in ovarian steroidogenesis, for two main reasons. First, the follicles are arranged in a distinct hierarchical order and their exact time to ovulation can easily be predicted from the time of oviposition of the previously ovulated follicle. Second, major components of the follicle walls, the granulosa and theca cells can be easily separated from one another.All follicles are exposed to a daily surge of LH, but only the largest follicle (FL) ovulates each day. This has been attributed to the ability of progesterone synthesis of F1 in response to LH. From the in vitro studies on steroidogenesis by ovarian cells of the Japanese quail, the following differences between F1 and small follicles have been clarifed:1. When stimulated with LH, the granulosa cells of F1 responded with a tenfold increase over unstimulated progesterone levels, whereas progesterone production in the granulosa cells of small follicles less than doubled.2. Activity of 17<alpha>-hydroxylase, which catalyzes the conversion of progesterone to 17<alpha>-hydroxyprogesterone, was high in the theca cells of small follicles. the theca cells of F1 and the granulosa cells of all follicles examined were essentially devoid of this enzyme. Similar tissue distribution was found for the activity of C17-C20 lyase, which convert 17<alpha>-hydroxyprogesterone to androstenedione.These findings indicate that when the follicle becomes the largest, not only the granulosa cells acquire the machinery for response to LH, but also the theca cells lose the enzyme activities, which metabolize progesterone to other steroids. In vivo studies using hypophysectomized quail reveal that these cellular chnges are under the influence of gonadotropins.