Pituitary-testicular responses of estradiol-17 beta-implanted bull calves to continuous versus pulsatile infusion of luteinizing hormone releasing hormone.
The luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone response of bull calves implanted with estradiol-17 beta to continuous and pulsatile infusion of luteinizing hormone releasing hormone (LHRH) has been examined. Estradiol-17 beta reduced serum LH and FSH concentrations and suppressed testosterone secretion and testicular growth when compared with sham-implanted bulls. Pulsatile iv infusion of LHRH [500 ng every 2 h (6 micrograms/d)] for a 4-wk period to estradiol-17 beta-implanted bulls resulted in elevated mean serum LH and testosterone concentrations that were characterized by discrete secretory episodes. Mean serum FSH was also increased by LHRH pulse infusion, but LHRH-coupled secretory episodes were not apparent. Continuous infusion of LHRH (6 micrograms/d) did not increase the low serum gonadotropin levels observed in estradiol-17 beta-implanted calves. Testicular growth was normal in LHRH pulse-infused calves, but was markedly curtailed in continuously infused calves. These results suggest that estradiol-17 beta inhibits testicular development by blocking gonadotropin release at the level of the hypothalamus because pulsatile administration of LHRH can override the inhibitory effect by increasing LH and FSH secretion.
D000818:Animals; D002417:Cattle / Q000502:physiology*; D004343:Drug Implants; D004958:Estradiol / Q000008:administration & dosage / Q000494:pharmacology*; D005640:Follicle Stimulating Hormone / Q000097:blood*; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D007263:Infusions, Parenteral / Q000662:veterinary; D007275:Injections, Intravenous / Q000662:veterinary; D007986:Luteinizing Hormone / Q000097:blood*; D008297:Male; D010902:Pituitary Gland / Q000187:drug effects* / Q000502:physiology; D012741:Sexual Maturation; D013737:Testis / Q000187:drug effects* / Q000502:physiology; D013739:Testosterone / Q000097:blood*
D004343:Drug Implants; D007987:Gonadotropin-Releasing Hormone; D013739:Testosterone; D004958:Estradiol; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone