title: Hypothalamic sites of action for testosterone, dihydrotestosterone, and estrogen in the regulation of luteinizing hormone secretion in male sheep.
abstract: Testosterone (T) inhibits LH secretion partly by acting at unknown sites within the brain to inhibit GnRH secretion. We tested the hypothesis that the preoptic area (POA) and arcuate-ventromedial region (ARC/VMR), areas rich in androgen and estrogen (E) receptors, are neural sites at which T and the T metabolites, dihydrotestosterone (DHT) and estrogen (E), act to suppress LH secretion. Bilateral guide cannulae were surgically implanted into either the POA or ARC/VMR of castrated male sheep. Experiments were conducted under a long day photoperiod to maximize the inhibitory effect of the steroids. In Exp 1, all sheep (n = 6/site) sequentially received bilateral implants of cholesterol (CHOL), T, or E at each site. Jugular blood samples were taken at 10-min intervals for 4 h both immediately before implant insertion and 5 days later. In Exp 2, all sheep (n = 6/site) sequentially received bilateral implants of CHOL, DHT, or E at each site according to a latin square design. Blood samples were taken before and 7 days after implant insertion. In Exp 3, which followed the same design as Exp 2, implants of E, T, or DHT were placed only in the ARC/VMR. In the final experiment, the effects of T and CHOL implants in the ARC/VMR were compared. Neither T, DHT, nor CHOL implants at either site affected LH secretion. In contrast, E treatment in the ARC/VMR suppressed mean plasma LH levels (P < 0.01), primarily due to an increase in interpulse interval (P < 0.01). Estrogen implants in the POA caused a small, but nonsignificant (P > 0.05), decrease in mean LH levels in the first experiment and an increase in LH interpulse interval (P < 0.05) in the second experiment. These results suggest that the ARC/VMR and possibly the POA are sites at which E acts to reduce GnRH secretion in male sheep.
authors.affiliation: Department of Veterinary Biosciences, University of Illinois, Urbana 61801, USA.
authors.forename: C J
authors.initials: CJ
authors.lastname: Scott
authors.forename: D E
authors.initials: DE
authors.lastname: Kuehl
authors.forename: S A
authors.initials: SA
authors.lastname: Ferreira
authors.forename: G L
authors.initials: GL
authors.lastname: Jackson
mesh_terms: D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000187:drug effects / Q000502:physiology; D002784:Cholesterol / Q000008:administration & dosage / Q000494:pharmacology; D004058:Diffusion; D013196:Dihydrotestosterone / Q000008:administration & dosage / Q000494:pharmacology*; D004343:Drug Implants; D004967:Estrogens / Q000008:administration & dosage / Q000494:pharmacology*; D005246:Feedback; D007031:Hypothalamus / Q000187:drug effects* / Q000502:physiology; D007033:Hypothalamus, Middle / Q000187:drug effects / Q000502:physiology; D007986:Luteinizing Hormone / Q000378:metabolism*; D008297:Male; D011301:Preoptic Area / Q000187:drug effects / Q000502:physiology; D012756:Sheep / Q000502:physiology*; D013739:Testosterone / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D004343:Drug Implants; D004967:Estrogens; D013196:Dihydrotestosterone; D013739:Testosterone; D007986:Luteinizing Hormone; D002784:Cholesterol