The main aims of the studies described in this thesis were firstly to determine the source of inhibin from the ovary of the sheep, and secondly to investigate the physiological role of inhibin in the control of gonadotrophin production, particularly that of FSH. The source of ovarian inhibin production was investigated by measuring inhibin secretion directly from the ovary <i>in vivo</i>, and by individual follicles <i>in vitro</i>. Inhibin secretion did not differ between animals at different stages of the luteal and follicular phase of the oestrous cycle. The secretion rate of inhibin was unaffected by the presence or absence of luteal tissue leading to the suggestion that, in the sheep, the corpus luteum does not produce significant quantities of inhibin. The results of these studies indicated that, like oestradiol, the majority of inhibin is produced by large (≥3mm) antral follicles. However, while most oestradiol was secreted by the large oestrogenic follicle(s), a significant amount of inhibin was also produced by large non-oestrogenic atretic follicles and by small antral follicles. A series of experiments involving passive immunisation against inhibin and/or oestradiol were then undertaken to investigate the relative importance of these two hormones in the control of gonadotrophin production. Peripheral LH concentrations were unaffected by immunisation against inhibin, and in a further experiment administration of inhibin in 'steroid stripped' ovine follicular fluid was shown to have no effect on the timing or magnitude of the oestradiol benzoate-induced LH surge in ovariectomised ewes, or on the concentration of LH following acute ovariectomy. In the passive immunisation studies, injection of antibodies to inhibin or oestradiol resulted in a highly significant, though transitory rise in the peripheral plasma concentration of FSH during both the luteal and follicular phases of the oestrus cycle, while combined immunisation against both hormones resulted in a significantly larger rise in FSH concentration of similar size to that seen following acute ovariectomy. Furthermore, treatment with physiological quantities of inhibin or oestradiol was found to partly prevent the rise in FSH concentration seen following acute ovariectomy, while a combined treatment with both hormones completely prevented this rise. Finally, immunisation against inhibin or oestradiol was shown to cause a large increase in the number of follicles per ovary, resulting in an increase in ovarian inhibin secretion following immunisation against oestradiol, and an increase in ovarian oestradiol secretion following immunisation against inhibin. These results indicate that inhibin plays an important physiological role in the control of FSH secretion during both the luteal and follicular stages of the sheep oestrous cycle, and suggest that inhibin and oestradiol act together in the control of FSH secretion.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:657272 |
| Date | January 1991 |
| Creators | Mann, George Edward |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/19978 |
Page generated in 0.0016 seconds