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Control of the koala (Phascolarctos cinereus) anterior pituitary-gonadal axis with analogues of GnRH

Camryn D. AllenA,H, Michelle BurridgeB, Mandy L. ChaferB, Vere N. NicolsonB, Sophia C. JagoB, Rosemary J. BoothC, Grant FraserC, Traza-Jade EnsabellaC, Yeng Peng ZeeA, Geoff Lundie-JenkinsC,
William V. HoltD, Allan T. LisleE, Frank N. CarrickF, Jonathan D. CurlewisG, Michael J. D’OcchioA and Stephen D. JohnstonA

ASchool of Animal Studies, The University of Queensland, Gatton, Queensland 4343, Australia.
BDreamworld, Coomera, Queensland 4209, Australia.
CEnvironmental Protection Agency, Brisbane, Queensland 4000, Australia.
DInstitute of Zoology, Regents Park, London NW1 4RY, England.
ESchool of Land, Crop and Food Sciences, The University of Queensland, St Lucia, Queensland 4072, Australia.
FCentre for Mined Land Rehabilitation, The University of Queensland, St Lucia, Queensland 4072, Australia.
GSchool of Biomedical Sciences, The University of Queensland, St Lucia, Queensland 4072, Australia.
HCorresponding author. Email:

ABSTRACT
The aim of the present study was to determine whether analogues of gonadotrophin-releasing hormone (GnRH) could be used to both induce an acute testosterone response and suppress anterior pituitary function in male koalas, and induce a luteal phase in female koalas. Experiment 1 characterised the steroidogenic response of male koalas to administration of 30 µg (4.3 µg kg−1) natural-sequence GnRH. Intra-muscular injection of natural-sequence GnRH induced the release of LH and testosterone with peak concentrations at 30 min (3.7 ± 1.9 ng mL−1) and 2 h (5.4 ± 0.5 ng mL−1), respectively. In Experiment 2, a single injection of the GnRH antagonist acyline (100 µg (14.3 µg kg−1) or 500 µg (71.4 µg kg−1)) did not influence the testosterone response to subsequent injections of natural-sequence GnRH. In Experiment 3, 4 µg (∼0.67 µg kg−1) of the GnRH agonist buserelin induced a luteal phase in five female koalas based on a LH surge, secretion of progestogen, and a normal-length oestrous cycle. The findings have shown that (1) natural-sequence GnRH can be used to test gonadotroph cell function and determine the testosterone-secreting capacity of male koalas, (2) the GnRH antagonist, acyline, at the dose rates used, does not suppress the pituitary-testis axis in male koalas, and (3) the GnRH agonist, buserelin, induces a normal luteal phase in female koalas.

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