Production of steroids by the ovary of the Japanese quail

Onagbesan, Mohammed Okanlawon (1982) Production of steroids by the ovary of the Japanese quail. University of Southampton, Doctoral Thesis.

Abstract

This study examined the production of steroid hormones (progesterone, testosterone, oestradiol and oestrone) by ovarian follicles of the Japanese quail in relation to age and sexual maturity; the mechanisms of action of and control by pituitary hormones of steroid production, oviposition and ovulation during the ovulatory cycle of the laying quail were investigated. Female quail raised on a short photoperiod (8L:16D) remained sexually immature while those raised on a long photoperiod (16L:SD) became sexually mature. Plasma steroid hormone levels rose significantly just before the onset of lay, explaining the observed oviduct growth, yolk-formation, follicle growth, induction of first ovulation and onset of lay which were absent in photosuppressed birds. The sites and relative amounts of steroids produced in the hierarchy of follicles were investigated. The largest follicles produced predominantly progesterone while the medium-sized follicles produced oestrogen. An histochemical study performed on the yolk-filled follicles revealed that the granuloss and theca cells in the follicle contained 30-HSDH and 1 7P-HSDH enzyme respectively. These sites parallel the postulated sites of steroidogenesis in chicken follicles. The distribution of these enzymes in the cells of the hierarchy of follicles parallel the relative amounts and types of steroids produced in vitro. Ovine LH and HCG stimulated progesterone and testosterone production by the cells dispersed from the yolk-filled follicles using collagenase while oFSH stimulated oestrogen production. The responsiveness to LH and HCG increased with the size of the follicle while the responsiveness to oFSE decreased with size. The mechanisms of action of these hormones were shown to involve the adenylate cyclase system. Experiments were designed to study the underlying causes of the changes in steroid hormone levels during the ovulatory cycle of the quail. In vitro, steroid production by follicular cell::-harvested at 12, 6 and 2 hrs before the expected ovulation time showed that the capacity for steroid production during the cycle change both at basal level and in response to putative hormones. Generally steroid production increases in all follicles up to the time of the endogenous LH surge and decreased after it. The duration of this desensitization varied among follicles: the F2 resumed steroid production 2 bra before ovulation while the F1 did not. Injections of LH or LH RE 18 and 12 hrs before ovulation also caused differential increases in progesterone levels in the plasma. It is proposed that LH and PSH control steroidogenesis in the ovary of the quail and also through stimulation and desensitization control the transition of one follicle to another. Studies on the control of oviposition and ovulation by injections of LE, LH-RH and progesterone indicated that the exogenous LH surge causes ovulation and that LH release is controlled by hypothalamic LH-RH through progesterone feedback from the ovarian follicles. The existence of an ~ovarian rhythm~ in the production of an ovulation-inducing amount of progesterone through changes in the sensitivity of the follicular cells to gonadotrophin stimulation during the ovulatory cycle was demonstrated.

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