title: The development of a testosterone stimulation test in the Virginia opossum (Didelphis virginiana) and its use in evaluating deslorelin contraception.
abstract: The aims of the present study were to examine the variability of testosterone secretion in the Virginia Opossum over a 24 h period and to develop a testosterone stimulation test that would provide an index of the prevailing testosterone biosynthetic capacity of the testes; the latter was used to clinically evaluate the efficacy of a gonadotrophin-releasing hormone agonist contraceptive. Sexually-mature captive opossums (n = 12) located in Africam Safari (Mexico) sampled every 12 h over 24 h consistently showed basal (<0.21 ng mL(-1)) blood testosterone concentrations. Intra-muscular injection of buserelin (2 microg mL(-1)) and human chorionic gonadotrophin (hCG; 1000 IU) resulted in an increase (P < 0.05) of plasma testosterone concentrations with maximal concentrations (3.9 ng mL(-1) and 5.8 ng mL(-1) respectively) occurring 120 min after injection. Plasma testosterone declined relatively rapidly to basal concentrations after 240 min with hCG but remained elevated after the same period of time with buserelin. Male opossums treated with (n = 6) and without (n = 6) a controlled-release deslorelin implant (Suprelorin; 4.7 mg deslorelin) were evaluated over a 10-week period for changes in testosterone secretion (hCG stimulation test) and sperm production (spermatorrhea). At the end of this period, the animals were hemi-castrated and their relative testicular quantitative histology compared. Testosterone concentration decreased over the course of the study in both treated and control animals (P < 0.0001) but there was no apparent effect of deslorelin on testosterone secretion, testicular histology (relative proportions of testicular cell types and seminiferous tubule diameter), or sperm production (presence of sperm in the cauda epididymis or urine).
authors.affiliation: School of Animal Studies, The University of Queensland, Gatton, Queensland 4343, Australia. s.johnston1@uq.edu.au
authors.forename: S D
authors.initials: SD
authors.lastname: Johnston
authors.forename: F C
authors.initials: FC
authors.lastname: Camacho
authors.forename: L
authors.initials: L
authors.lastname: Carrillo
authors.forename: N
authors.initials: N
authors.lastname: Guy
authors.forename: J
authors.initials: J
authors.lastname: Govea
authors.forename: O
authors.initials: O
authors.lastname: Martinez
authors.forename: A
authors.initials: A
authors.lastname: Parãs
authors.forename: A T
authors.initials: AT
authors.lastname: Lisle
authors.forename: M
authors.initials: M
authors.lastname: D'Occhio
mesh_terms: D000818:Animals; D002064:Buserelin / Q000008:administration & dosage / Q000627:therapeutic use; D006063:Chorionic Gonadotropin / Q000008:administration & dosage / Q000627:therapeutic use; D003267:Contraception / Q000379:methods* / Q000662:veterinary; D003272:Contraceptive Agents, Male / Q000008:administration & dosage / Q000627:therapeutic use; D003940:Diagnostic Techniques, Endocrine / Q000662:veterinary*; D004353:Drug Evaluation, Preclinical; D004343:Drug Implants; D008297:Male; D009893:Opossums / Q000378:metabolism / Q000502:physiology*; D009929:Organ Size / Q000187:drug effects; D013737:Testis / Q000033:anatomy & histology / Q000187:drug effects; D013739:Testosterone / Q000097:blood / Q000378:metabolism*; D017329:Triptorelin Pamoate / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000627:therapeutic use
chemical_list: D006063:Chorionic Gonadotropin; D003272:Contraceptive Agents, Male; D004343:Drug Implants; D017329:Triptorelin Pamoate; D013739:Testosterone; D002064:Buserelin; C066438:deslorelin