The development of a testosterone stimulation test in the Virginia opossum (Didelphis virginiana) and its use in evaluating deslorelin contraception

摘要

The aims of the present study were to examine the variability of testosterone secretion in theVirginia Opossumnover a 24 h period and to develop a testosterone stimulation test that would provide an index of the prevailing testosteronenbiosynthetic capacity of the testes; the latter was used to clinically evaluate the efficacy of a gonadotrophin-releasingnhormone agonist contraceptive. Sexually-mature captive opossums (n=12) located in Africam Safari (Mexico) samplednevery 12 h over 24 h consistently showed basal (<0.21 ngmL−1) blood testosterone concentrations. Intra-muscular injectionnof buserelin (2μgmL−1) and human chorionic gonadotrophin (hCG; 1000 IU) resulted in an increase (P <0.05) ofnplasma testosterone concentrations with maximal concentrations (3.9 ngmL−1 and 5.8 ngmL−1 respectively) occurringn120 min after injection. Plasma testosterone declined relatively rapidly to basal concentrations after 240 min with hCGnbut remained elevated after the same period of time with buserelin. Male opossums treated with (n=6) and withoutn(n=6) a controlled-release deslorelin implant (Suprelorin; 4.7 mg deslorelin) were evaluated over a 10-week period fornchanges in testosterone secretion (hCG stimulation test) and sperm production (spermatorrhea). At the end of this period,nthe animals were hemi-castrated and their relative testicular quantitative histology compared. Testosterone concentrationndecreased over the course of the study in both treated and control animals (P <0.0001) but there was no apparent effectnof deslorelin on testosterone secretion, testicular histology (relative proportions of testicular cell types and seminiferousntubule diameter), or sperm production (presence of sperm in the cauda epididymis or urine)