Control of the koala (Phascolarctos cinereus) anterior pituitary-gonadal axis with analogues of GnRH.
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 microg (4.3 microg 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 microg (14.3 microg kg(-1)) or 500 microg (71.4 microg kg(-1))) did not influence the testosterone response to subsequent injections of natural-sequence GnRH. In Experiment 3, 4 microg (~0.67 microg 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.
Allen
Camryn D
CD
School of Animal Studies, The University of Queensland, Gatton, Queensland 4343, Australia. callen@salk.edu
Burridge
Michelle
M
Chafer
Mandy L
ML
Nicolson
Vere N
VN
Jago
Sophia C
SC
Booth
Rosemary J
RJ
Fraser
Grant
G
Ensabella
Traza-Jade
TJ
Zee
Yeng Peng
YP
Lundie-Jenkins
Geoff
G
Holt
William V
WV
Lisle
Allan T
AT
Carrick
Frank N
FN
Curlewis
Jonathan D
JD
D'Occhio
Michael J
MJ
Johnston
Stephen D
SD
D000818:Animals; D002064:Buserelin / Q000494:pharmacology*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000819:agonists / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors; D006066:Gonads / Q000187:drug effects* / Q000502:physiology; D006727:Hormone Antagonists / Q000494:pharmacology; D008297:Male; D009842:Oligopeptides / Q000494:pharmacology*; D010062:Ovulation Induction / Q000662:veterinary; D048368:Phascolarctidae / Q000097:blood / Q000502:physiology*; D010901:Pituitary Function Tests; D010902:Pituitary Gland / Q000187:drug effects* / Q000502:physiology; D013739:Testosterone / Q000097:blood
D006727:Hormone Antagonists; D009842:Oligopeptides; D007987:Gonadotropin-Releasing Hormone; D013739:Testosterone; D002064:Buserelin; C109238:acyline