title: Differential testosterone response to GnRH-induced LH release before and after musth in adult Asian elephant (Elephas maximus) bulls.
abstract: Bull elephants exhibit marked increases in testosterone secretion during musth, and studies have shown a heightened sensitivity of the testis to GnRH-stimulated testosterone production in musth compared to nonmusth males. However, activity of the hypothalamo-pituitary-gonadal axis before or soon after musth has not been studied in detail. The aim of this study was to evaluate LH and testosterone responses to GnRH challenge in nine adult Asian elephant (Elephas maximus) bulls during three periods relative to musth: premusth, postmusth, and nonmusth. Bulls were administered 80 μg of a GnRH agonist, and blood was collected before and after injection to monitor serum hormone concentrations. The same bulls were injected with saline 2 weeks before each GnRH challenge and monitored using the same blood collection protocol. All bulls responded to GnRH, but not saline, with an increase in LH and testosterone during all three periods. The mean peak LH (1.76 ± 0.19 ng/mL; P < 0.001) and testosterone (6.71 ± 1.62 ng/mL; P = 0.019) concentrations after GnRH were higher than the respective baselines (0.57 ± 0.07 ng/mL, 3.05 ± 0.60 ng/mL). Although basal- and GnRH-induced LH secretion were similar across the stages, evaluation of the area under the curve in GnRH-treated bulls indicated that the testosterone response was greatest during premusth (2.84 ± 0.76 area units; P = 0.019) compared to postmusth (2.02 ± 0.63 area units), and nonmusth (2.01 ± 0.46 area units). This confirms earlier reports that GnRH stimulates LH release and subsequent testosterone production in bull elephants. Furthermore, although the hypothalamo-pituitary-gonadal axis is active throughout the year, the testis appears to be more responsive to LH in terms of testosterone production in the period leading up to musth, compared to the nonmusth and postmusth periods. This heightened sensitivity, perhaps as a result of LH receptor up-regulation, may prime the testis for maximal testosterone production, leading to the physiological and behavioral changes associated with musth.
authors.affiliation: Department of Companion Animal and Wildlife Clinics, Faculty of Veterinary Medicine, Chiang Mai University, Chiang Mai, Thailand; Center of Excellence in Elephant Research and Education, Chiang Mai University, Chiang Mai, Thailand. Electronic address: chaleamchat.s@cmu.ac.th.
authors.forename: Chaleamchat
authors.initials: C
authors.lastname: Somgird
authors.affiliation: Center of Excellence in Elephant Research and Education, Chiang Mai University, Chiang Mai, Thailand.
authors.forename: Supaphen
authors.initials: S
authors.lastname: Sripiboon
authors.affiliation: Thai Elephant Conservation Center, National Elephant Institute, Forest Industry Organization, Lampang, Thailand.
authors.forename: Sittidet
authors.initials: S
authors.lastname: Mahasawangkul
authors.affiliation: Thai Elephant Conservation Center, National Elephant Institute, Forest Industry Organization, Lampang, Thailand.
authors.forename: Khajohnpat
authors.initials: K
authors.lastname: Boonprasert
authors.affiliation: Smithsonian Conservation Biology Institute, Smithsonian Institution, Front Royal, Virginia, USA.
authors.forename: Janine L
authors.initials: JL
authors.lastname: Brown
authors.affiliation: Faculty of Veterinary Medicine, Utrecht University, CM, Utrecht, The Netherlands; Faculty of Veterinary Sciences, University of Pretoria, South Africa.
authors.forename: Tom A E
authors.initials: TA
authors.lastname: Stout
authors.affiliation: Faculty of Veterinary Medicine, Utrecht University, CM, Utrecht, The Netherlands.
authors.forename: Ben
authors.initials: B
authors.lastname: Colenbrander
authors.affiliation: Department of Companion Animal and Wildlife Clinics, Faculty of Veterinary Medicine, Chiang Mai University, Chiang Mai, Thailand; Center of Excellence in Elephant Research and Education, Chiang Mai University, Chiang Mai, Thailand. Electronic address: chatchote.thitaram@cmu.ac.th.
authors.forename: Chatchote
authors.initials: C
authors.lastname: Thitaram
mesh_terms: D000818:Animals; D004334:Drug Administration Schedule; D004606:Elephants / Q000502:physiology*; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000502:physiology*; D008297:Male; D012726:Sexual Behavior, Animal / Q000502:physiology*; D013739:Testosterone / Q000097:blood
chemical_list: D007987:Gonadotropin-Releasing Hormone; D013739:Testosterone; D007986:Luteinizing Hormone
keywords: Asian elephant (Elephas maximus); GnRH agonist; Hypothalamo-pituitary-gonadal (HPG) axis; LH; Musth; Testosterone