Effect of Naltrexone on photoperiodic regulation of testicular steroidogenesis in adult golden hamster, Mesocricetus auratus

摘要

Photoperiodic regulation of testicular steroidogenesis through modulation of MT1R expression and local melatonin content is well established. However, additional mediators besides local melatonergic system in photoperiodic control of testicular steroidogenesis in golden hamster have not been studied in detail. Endogenous opioid peptides (EOP) are known to regulate reproduction via acting at multiple levels of the hypothalamus-pituitary-gonadal (HPG) axis. The presence of beta-endorphin, a naturally occurring opioid peptide, and its receptor (mu-opioid receptor, mu OR) has been reported in rat testes; however the functional significance of photoperiodic regulation mu OR in testicular steroidogenesis is not clear. In the present study, we assessed the effect of Naltrexone (Nal), a mu OR antagonist, in photoperiodic regulation of testicular steroidogenesis. Immunohistochemical (IHC) localization and expression of mu OR along with the expression of steroidogenic markers in testes was analyzed through western blot analyses. IHC suggest immunoreactivity for mu OR in Leydig cells with strong immunoreactivity under SD (short-day) condition, whereas weak immunoreactivity was observed under LD (long-day). The expression of mu OR was significantly decreased following Nal administration in both the photoperiodic conditions. The localization and differential photoperiodic regulation of mu OR in Leydig cells suggests its involvement in testicular steroidogenesis. Further, Nal administration significantly increased the expression of steroidogenic markers (AR, StAR, P450(scc). LH-R, 3 beta-HSD and 17-HSD) and plasma testosterone concentration under SD condition as compared to SD-control. We may therefore suggest that photoperiod differentially regulates the expression of mu OR which thereby mediates the inhibitory effect of melatonin on testicular steroidogenesis. (C) 2015 Elsevier Inc. All rights reserved.