title: Further characterization of the direct inhibitory effect of LHRH agonists at the testicular level in the rat.
abstract: To further clarify the relative importance of the pituitary and gonadal sites of LHRH action, intact and hypophysectomized adult male rats were treated with hCG for 7 days, in the presence or absence of simultaneous treatment with increasing doses of the LHRH agonist [D-Ser(TBU)6des-Gly-NH2(10)]LHRH ethylamide, Buserelin (0.025, 0.25, 2.5 or 25 micrograms/rat, twice daily). Daily treatment of intact adult rats with hCG (25 IU) markedly increased ventral prostate and seminal vesicle weight, while a dose-dependent inhibition of the effect was observed following combined administration of Buserelin. In hypophysectomized rats, treatment with hCG resulted in a partial restoration of ventral prostate and seminal vesicle weight, while combined treatment with a high dose of the LHRH agonist (25 micrograms, twice daily) partially (P less than 0.05) inhibited the stimulatory effect of hCG. LH/hCG receptors were almost completely inhibited after hCG injection alone and a further decrease was observed in the presence of simultaneous LHRH agonist treatment. The hCG-induced stimulation of GH/PRL receptors was counteracted by Buserelin treatment in hypophysectomized animals. The present data demonstrate that although LHRH-induced LH release has been shown to play a major role in the loss of testicular functions induced by low doses of LHRH agonists in the rat, a direct inhibitory action of LHRH agonists can be exerted at the testicular level at high doses of the peptide.
mesh_terms: D000818:Animals; D002064:Buserelin / Q000494:pharmacology*; D006063:Chorionic Gonadotropin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005837:Genitalia, Male / Q000187:drug effects*; D007016:Hypophysectomy; D008297:Male; D009929:Organ Size / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000378:metabolism; D011974:Receptors, LH; D011981:Receptors, Prolactin; D011986:Receptors, Somatotropin
chemical_list: D006063:Chorionic Gonadotropin; D011956:Receptors, Cell Surface; D011974:Receptors, LH; D011981:Receptors, Prolactin; D011986:Receptors, Somatotropin; D002064:Buserelin