EVIDENCE FOR THE PRESENCE OF IMMUNOREACTIVE INHIBIN IN EXTRAGONADAL TISSUES OF OVARIECTOMIZED EWES

Six ewes were ovariectomized to determine the immediate and long-term effects of removal of ovaries on the immunoreactive concentrations of FSH, LH and inhibin. Three months after ovariectomy, ewes were slaught ered and tissue samples of brain, pituitary, spleen, liver, perirenal fat, lung, kidney, adrenals and uterus were collected to determine the immunoreactive inhibin content, Both gonadotrophins, FSH and LH, incr eased significantly after ovariectomy. The increase of FSH, however, w as more pronounced and remarkably faster than the changes of LH after ovariectomy. Immunoreactive concentrations of inhibin decreased sharpl y as early as 15 min after ovariectomy and subsequently decreased more gradually until 2 weeks after surgery, From this moment on, the level stabilized at 56% of the initial value. In control ewes, a considerab le amount of immunoreactive inhibin is found in tissue samples of ovar y, lung, kidney, pituitary and spleen. After ovariectomy, the level of immunoreactive inhibin decreased in spleen and lung samples while an important increase of immunoreactive inhibin is found in adrenals and pituitary. These results demonstrate a differential regulation of LH a nd FSH after ovariectomy and support an involvement of inhibin only in the immediate changes of FSH after ovariectomy in sheep. They further suggest that the adrenals and the pituitary may be extragonadal sourc es of inhibin. To explore the eventual contribution of the adrenals to circulating inhibin, dexamethasone (1.4 mg/ewe) and ACTH (200 IU/ewe) were in following experiment injected intravenously in control and ov ariectomized ewes. The lack of any effect of dexamethasone: or ACTH on the plasma concentration of immunoreactive: inhibin indicate that adr enal inhibin probably does not contribute to circulating inhibin. (C) 1997 Elsevier Science B.V.