title: Effect of testosterone on the hypothalamic-pituitary-testicular axis of the old male rat.
abstract: Old rats show lower serum testosterone, a lower increase in serum LH either after orchidectomy or after LHRH stimulation, and a lower number of hCG binding sites in testis, compared to younger controls. Treatment with testosterone for 5 to 6 weeks was followed by an increment in the androgen serum levels of about 70% in adult, and of 170% in old animals, a reduction to about one half testicular weight in both groups, and an inhibition of similar magnitudes in the LH increase that followed castration or LHRH stimulation. Testosterone treatment reduced the binding sites for hCG in testis of young rats but did not correct the already low values observed in the old animals. It is suggested that similarities and differences occur in the hypothalamic-pituitary-testicular axis of young and old animals and that differences could be due to changes in set points regulation of the system and/or some intrinsic modification of the hormone producing mechanisms.
mesh_terms: D000818:Animals; D002369:Castration; D006063:Chorionic Gonadotropin / Q000378:metabolism; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D007030:Hypothalamo-Hypophyseal System / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D007986:Luteinizing Hormone / Q000378:metabolism; D008297:Male; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism; D011974:Receptors, LH; D013737:Testis / Q000187:drug effects / Q000502:physiology*; D013739:Testosterone / Q000494:pharmacology*
chemical_list: D006063:Chorionic Gonadotropin; D011956:Receptors, Cell Surface; D011974:Receptors, LH; D007987:Gonadotropin-Releasing Hormone; D013739:Testosterone; D007986:Luteinizing Hormone