Pituitary and testicular endocrine responses to exogenous gonadotrophin-releasing hormone (GnRH) and luteinising hormone in male dogs treated with GnRH agonist implants
A. Junaidi A B E F , P. E. Williamson A , G. B. Martin B , P. G. Stanton C , M. A. Blackberry B , J. M. Cummins A and T. E. Trigg DA Division of Veterinary and Biomedical Sciences, Murdoch University, Perth, Murdoch, WA 6150, Australia.
B School of Animal Biology, The University of Western Australia, Crawley, WA 6009, Australia.
C Prince Henry’s Institute of Medical Research, Clayton, Victoria 3168, Australia.
D Peptech Animal Health Pty Limited, 19–24 Khartoum Road, Macquarie Park, NSW 2133, Australia.
E Present address: Faculty of Veterinary Medicine, Gadjah Mada University, J1. Olahraga - Karangmalang, Yogyakarta 55281, Indonesia.
F Corresponding author. Email: arjunavet03@yahoo.com
Reproduction, Fertility and Development 19(8) 891-898 https://doi.org/10.1071/RD07088
Submitted: 8 June 2007 Accepted: 6 August 2007 Published: 11 September 2007
Abstract
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 μg kg–1 bodyweight, i.v.) was injected on Days 15, 25, 40 and 100 after implantation, whereas bovine LH (0.5 μg 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.
Additional keywords: desensitisation, deslorelin, testosterone.
Acknowledgements
Assay reagents for canine LH were supplied by Dr A. F. Parlow (Director, Pituitary Hormones and Antisera Center, Harbor-UCLA Medical Center, Torrance, CA, USA). The authors are indebted to James Murray for expert technical help.
Akhtar, F. B. , Marshall, G. R. , Wickings, E. J. , and Nieschlag, E. (1983). Reversible induction of azoospermia in rhesus monkeys by constant infusion of a gonadotropin releasing hormone agonist using osmotic minipumps. J. Clin. Endocrinol. Metab. 56, 534–540.
| PubMed |
Vickery, B. H. , and McRae, G. I. (1980). Effects of continuous treatment of male baboons with super agonists of LHRH. Int. J. Fertil. 25, 179–184.
| PubMed |
Vickery, B. H. , Georgia, I. M. , Briones, W. , Worden, A. , Seidenberg, R. , Schanbacher, B. D. , and Falvo, R. (1984). Effects of an LHRH agonist analog upon sexual function in male dogs. J. Androl. 5, 28–42.
| PubMed |
Vickery, B. H. , McRae, G. I. , Briones, W. V. , Roberts, B. B. , Worden, A. C. , Schanbacher, B. D. , and Falvo, R. E. (1985). Dose–response studies on male reproductive parameters in dogs with nafarelin acetate, a potent LHRH agonist. J. Androl. 6, 53–60.
| PubMed |
Ward, J. A. , Furr, B. J. A. , Valcaccia, B. , Curry, B. , Bardin, C. W. , Gunsalus, G. I. , and Morris, I. D. (1989). Prolonged suppression of rat testis function by depot formulation of Zoladex, a GnRH agonist. J. Androl. 10, 478–486.
| PubMed |
