title: Photoperiod affects the ability of testosterone to alter proopiomelanocortin mRNA, but not luteinizing hormone-releasing hormone mRNA, levels in male sheep.
abstract: This study tested the hypothesis that photoperiod affects the ability of testosterone to reduce proopiomelanocortin (POMC) mRNA levels in the arcuate nucleus and luteinizing hormone-releasing hormone (LHRH) mRNA levels in both the preoptic area (POA) or medial basal hypothalamus (MBH). Twenty castrated male sheep were assigned to one of four treatment groups (i): short days (SD; n=5) (ii), short days with testosterone (SD+T; n=5) (iii), long days (LD; n=5), or (iii) long days with testosterone (LD+T; n=5). Blood samples were collected twice weekly for the last 3 weeks of photoperiod treatment and assessed for LH to validate the response to photoperiod. After evaluating LH levels, one animal each from the LD+T and SD+T groups was excluded from the analyses. Mean concentrations of LH were lower (P<0.01) in the LD+T group than in the other treatment groups, which did not differ (P>0.10) from each other. Neither POA nor MBH LHRH mRNA levels were affected (P>0.10) by treatment. Conversely, POMC mRNA levels were suppressed (P<0.01) in the LD+T males compared with the other treatment groups which did not differ (P>0.10) from each other. These observations suggest that photoperiod specific, testosterone-induced alterations in LHRH mRNA levels are not a mechanism whereby testosterone suppresses LHRH release, and that increased beta-endorphin synthesis and release do not mediate testosterone-induced seasonal suppression of LHRH release.
authors.affiliation: Department of Veterinary Biosciences, University of Illinois, Urbana 61802, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Hileman
authors.forename: D E
authors.initials: DE
authors.lastname: Kuehl
authors.forename: G L
authors.initials: GL
authors.lastname: Jackson
mesh_terms: D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D007987:Gonadotropin-Releasing Hormone / Q000235:genetics*; D007033:Hypothalamus, Middle / Q000378:metabolism; D007986:Luteinizing Hormone / Q000097:blood; D008297:Male; D009919:Orchiectomy; D017440:Photoperiod; D011301:Preoptic Area / Q000378:metabolism; D011333:Pro-Opiomelanocortin / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism*; D012756:Sheep / Q000378:metabolism*; D013739:Testosterone / Q000097:blood / Q000494:pharmacology*
chemical_list: D012333:RNA, Messenger; D007987:Gonadotropin-Releasing Hormone; D013739:Testosterone; D011333:Pro-Opiomelanocortin; D007986:Luteinizing Hormone