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Effects of a Gonadotropin-Releasing Hormone Agonist Implant on Reproduction in a Male Marsupial, Macropus eugenii¹

Department of Biological Sciences,³ Macquarie University, North Ryde, New South Wales 2109, Australia Peptech Animal Health Pty. Limited,⁴ North Ryde, New South Wales 2109, Australia Department of Zoology,⁵ University of Melbourne, Victoria 3010, Australia AgResearch,⁶ Wallaceville Animal Research Centre, Upper Hutt, New Zealand

This study evaluated the potential of slow-release GnRH agonist (deslorelin) implants to inhibit reproductive function in the male tammar wallaby. The specific aim was to measure the effects of graded dosages of deslorelin on testes size and plasma LH and testosterone concentrations. Adult male tammar wallabies were assigned to four groups (n = 6 per group) and received the following treatment: control, placebo implant; low dose, 5 mg deslorelin; medium dose, 10 mg; high dose, 20 mg. All dosages of deslorelin induced acute increases (P < 0.001) in plasma LH and testosterone concentrations within 2 h, with concentrations remaining elevated during the first 24 h but returning to pretreatment levels by Day 7. Thereafter, there was no evidence of a treatment-induced decline in plasma testosterone concentrations. There was no detectable difference in basal LH concentrations between treated and control animals, nor was there a significant change in testes width or length (P > 0.05). These results suggest that the male tammar wallaby is resistant to the contraceptive effects of chronic GnRH agonist treatment. Despite the maintenance of testosterone secretion, the majority of male tammars (10 of 17) failed to respond to a GnRH challenge with a release of LH between Days 186 and 197 of treatment. The failure of animals to respond to exogenous GnRH suggests a direct effect of deslorelin on the pituitary, resulting in a level of desensitization that was sufficient to inhibit a LH surge but insufficient to inhibit basal LH secretion. The variation between animals is believed to result from earlier recovery of some individuals, in particular those that received a lower dose, or individual resistance to the desensitization process.

¹ Support was provided by the Australian Research Council Strategic Partnerships with Industry Research and Training Grant Number C00001980. C.A.H. was the recipient of an Australian Postgraduate Award.

² Correspondence. FAX: 61 2 9850 9686; cherbert{at}rna.bio.mq.edu.au

This article has been cited by other articles:

				C.A. Herbert, D.C. Eckery, T.E. Trigg, and D.W. Cooper Chronic Treatment of Male Tammar Wallabies with Deslorelin Implants During Pouch Life: Effects on Development, Puberty, and Reproduction in Adulthood Biol Reprod, June 1, 2007; 76(6): 1054 - 1061. [Abstract] [Full Text] [PDF]

				C A Herbert, T E Trigg, M B Renfree, G Shaw, D C Eckery, and D W Cooper Long-term effects of deslorelin implants on reproduction in the female tammar wallaby (Macropus eugenii) Reproduction, March 1, 2005; 129(3): 361 - 369. [Abstract] [Full Text] [PDF]