Introduction. Testicular function in the sand rodent Psammomys obesus is subjected to seasonal alternations with a trigger of spermatogenesis in winter and a total quiescence which extends from late spring to summer. The aim of this study was to investigate the distribution of b-endorphin in the testis at the period of winter sexual activity and at its summer regression, and assess the effect of 17 β-estradiol treatment on testicular morphology and b-endorphin expression.

Material and methods. The adult males were grouped into 4 groups (rest group, sexually active group, rest treated with 17β-estradiol group and controls at sexual rest injected with olive oil, n = 5 in each group). Using anti-serum against b-endorphin, we studied its testicular expression by Western blot and cellular location by immunohistochemical (IHC) method, respectively.

Results. We detected by Western blot a peptide of 3.5 kDa molecular weight corresponding to b-endorphin only in sexually resting and control males. The 17β-estradiol treatment induced a clear reduction in the b-endorphin band expression compared with the latter. These results were confirmed by the IHC analysis since b-endorphin was only observed in the testis at sexual rest and in controls, in majority of seminiferous tubules at the level of germ cells. The intensity of IHC labeling was significantly different between spermatogonia and spermatocytes I or round spermatids which revealed the strongest labeling. The intense immunoreactivity was also located in Leydig cells and highly significantly varied compared to the germ cells. The 17 β-estradiol treatment decreased significantly the β-endorphin signal in germ cells but not in Leydig cells.

Conclusion. The 17β-estradiol treatment induces a repressive effect on seasonal testicular endorphinergic system in P. obesus and this action targets exclusively the germ cells.