title: Minor interference of low-dose pulses of GnRH with the positive effect of oestradiol on the pituitary gland.
abstract: In the ovariectomized rat we investigated the effects of prolonged treatment with oestradiol and 'physiological' pulses of exogenous GnRH on the GnRH-responsiveness of the pituitary gland. Rats were for 20 h pre-treated with either GnRH (3-ng pulses of 3 min duration every 20 min) or saline and for 19 h with either oestradiolbenzoate (OB; 3 micrograms/sc injection) or oil. Then LH and FSH responses were evoked by continuous test infusions of GnRH at the rates of either 60, 100, 150 or 1000 ng/h, lasting 10 h. It appeared that, irrespective of pre-treatment with either GnRH or saline, OB caused an increase of the maximal LH and FSH responses (that is the responses to the maximal stimulus of 1000 ng GnRH/h), and an increase of the GnRH-sensitivity of the pituitary gland, as far as the FSH secretion is concerned. GnRH pulses caused, irrespective of pre-treatment with OB or oil, a decrease of the GnRH-sensitivity of the pituitary gland, as well as a decrease of the maximal FSH response and of the pituitary FSH content. It was concluded that low-dose pulses of exogenous GnRH desensitize the pituitary gland and deplete the pituitary FSH stores, but do not change the positive effect of oestradiol on the maximal gonadotropin response.
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D004958:Estradiol / Q000008:administration & dosage*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000378:metabolism; D007031:Hypothalamus / Q000187:drug effects; D007986:Luteinizing Hormone / Q000378:metabolism; D010052:Ovariectomy; D010902:Pituitary Gland / Q000187:drug effects*; D010906:Pituitary Hormone-Releasing Hormones / Q000008:administration & dosage*; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D010906:Pituitary Hormone-Releasing Hormones; D004958:Estradiol; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone