Seasonally and experimentally induced changes in testicular function of the Australian bush rat (Rattus fuscipes)

Publisher Website
Google Scholar
Abstract
Serum concentrations of LH [luteinizing hormone], FSH and testosterone were measured monthly throughout the year in male bush rats. Testicular size and ultrastructure, LH/hCG [human chorionic gonadotropin], FSH and estradiol receptors and the response of the pituitary to LHRH were also recorded. LH and FSH rose in parallel with an increase in testicular size after the winter solstice with peak gonadotropin levels in the spring (Sept.). The subsequent fall in LH and FSH levels was associated with a rise in serum testosterone which reached peak levels during summer (Dec. and Jan.). In Feb. serum testosterone levels and testicular size declined in parallel, while the pituitary response to an LHRH injection was maximal during late summer. The number of LH/hCG, FSH and estradiol receptors per testis were all greatly reduced in the regressed testes when compared to active testes. In a controlled environment of decreased lighting (shortened photoperiod), temperature and food quality, the testes of sexually active adult males regressed at any time of the year, the resultant testicular morphology and endocrine status being identical to that of wild rats in the nonbreeding season. Full testicular regression was achieved only when the photoperiod, temperature and food quality were changed: experiments in which only 1 or 2 of these factors were altered failed to produce complete sexual regression.