Pituitary and testicular endocrine responses to exogenous gonadotrophin-releasing hormone (GnRH) and luteinising hormone in male dogs treated with GnRH agonist implants.
The present study tested whether exogenous gonadotrophin-releasing hormone (GnRH) and luteinising hormone (LH) can stimulate LH and testosterone secretion in dogs chronically treated with a GnRH superagonist. Twenty male adult dogs were assigned to a completely randomised design comprising five groups of four animals. Each dog in the control group received a blank implant (placebo) and each dog in the other four groups received a 6-mg implant containing a slow-release formulation of deslorelin (d-Trp6-Pro9-des-Gly10-LH-releasing hormone ethylamide). The same four control dogs were used for all hormonal challenges, whereas a different deslorelin-implanted group was used for each challenge. Native GnRH (5 microg kg(-1) bodyweight, i.v.) was injected on Days 15, 25, 40 and 100 after implantation, whereas bovine LH (0.5 microg kg(-1) bodyweight, i.v.) was injected on Days 16, 26, 41 and 101. On all occasions after Day 25-26 postimplantation, exogenous GnRH and LH elicited higher plasma concentrations of LH and testosterone in control than deslorelin-treated animals (P < 0.05). It was concluded that, in male dogs, implantation of a GnRH superagonist desensitised the pituitary gonadotrophs to GnRH and also led to a desensitisation of the Leydig cells to LH. This explains, at least in part, the profound reduction in the production of androgen and spermatozoa in deslorelin-treated male dogs.
Junaidi
A
A
Division of Veterinary and Biomedical Sciences, Murdoch University, Perth, Murdoch, WA 6150, Australia. arjunavet03@yahoo.com
Williamson
P E
PE
Martin
G B
GB
Stanton
P G
PG
Blackberry
M A
MA
Cummins
J M
JM
Trigg
T E
TE
D000818:Animals; D002417:Cattle; D004285:Dogs / Q000502:physiology*; D004343:Drug Implants; D007987:Gonadotropin-Releasing Hormone / Q000819:agonists* / Q000097:blood / Q000494:pharmacology* / Q000502:physiology; D007986:Luteinizing Hormone / Q000378:metabolism / Q000494:pharmacology*; D008297:Male; D010902:Pituitary Gland / Q000187:drug effects*; D011897:Random Allocation; D013737:Testis / Q000187:drug effects*; D013739:Testosterone / Q000378:metabolism; D017329:Triptorelin Pamoate / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology
D004343:Drug Implants; D017329:Triptorelin Pamoate; D007987:Gonadotropin-Releasing Hormone; D013739:Testosterone; D007986:Luteinizing Hormone; C066438:deslorelin