Regulation of testicular steroidogenesis by gonadotropin-releasing hormone agonists and antagonists.
Clinical and experimental studies are described on the effects of a gonadotropin-releasing hormone (GnRH) agonist (A) and antagonist (Ant.) on testicular endocrine function. Testicular effects of long-term gonadotropin suppression by GnRH-A were assessed during treatment of prostatic cancer patients. The testis tissue removed after 6 months of A treatment had less than 5% of the testosterone(T)-producing capacity in comparison to testis tissue removed from untreated control patients. However, the LH receptors (R) and responsiveness of T output to LH stimulation in vitro were unchanged. FSH-R decreased by 70%. Hence, despite suppression of gonadotropins and testicular androgen production during long-term GnRH-A treatment the responsiveness to exogenous gonadotropins is maintained. The testicular effects of a gonadotropin suppression induced with GnRH-Ant. and testicular GnRH-R blockade were studied in rats. Besides decreases of gonadotropins and testicular T, systemic Ant. treatment decreased testicular Prl-R, but had no effect on LH-R or FSH-R. Bromocriptine-induced hypoprolactinemia, in contrast, decreased LH-R but had no effect on Prl-R. The results indicate reciprocal regulation of LH-R and Prl-R, and that testicular steroidogenesis and LH-R are under differential regulation, the former by LH, the latter by Prl. In another study, testicular GnRH-R, and consequently the action of a putative testicular GnRH-like factor, were blocked by unilateral intratesticular infusion of Ant. (1 week, Alzet osmotic pumps). The treatment resulted in 90% occupancy of testicular GnRH-R in the Ant.-infused testes, and this was associated with decreased levels of R for LH, FSH and Prl, and of T. The results indicated that the testicular GnRH-R have a physiological function in subtle stimulation of Leydig cell functions.
D000135:Acid Phosphatase / Q000097:blood; D000368:Aged; D000818:Animals; D002064:Buserelin / Q000494:pharmacology* / Q000627:therapeutic use; D005640:Follicle Stimulating Hormone / Q000097:blood; D006801:Humans; D007986:Luteinizing Hormone / Q000097:blood; D008297:Male; D008875:Middle Aged; D010906:Pituitary Hormone-Releasing Hormones / Q000037:antagonists & inhibitors / Q000276:immunology / Q000494:pharmacology*; D011471:Prostatic Neoplasms / Q000188:drug therapy; D051381:Rats; D011956:Receptors, Cell Surface / Q000032:analysis / Q000502:physiology; D011962:Receptors, FSH; D011974:Receptors, LH; D011966:Receptors, LHRH; D011981:Receptors, Prolactin; D013737:Testis / Q000187:drug effects* / Q000378:metabolism; D013739:Testosterone / Q000096:biosynthesis*
D010906:Pituitary Hormone-Releasing Hormones; D011956:Receptors, Cell Surface; D011962:Receptors, FSH; D011974:Receptors, LH; D011966:Receptors, LHRH; D011981:Receptors, Prolactin; D013739:Testosterone; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D000135:Acid Phosphatase; D002064:Buserelin