Cell apoptosis in the testis of male rats is elevated by intervention with beta-endorphin and the mu opioid receptor

beta-endorphin (beta-EP) is involved in the regulation of male germ cells; however, little is known about the effect of beta-EP on primary germ cells via opioid receptors. In this study, we first revealed significant cell apoptosis in the testis of male rats after beta-EP intervention. Subsequently, the expression of the mu opioid receptor (MOR) was detected in both Leydig cells (LCs) and spermatogonia (SGs) by fluorescence colocalization; overlapping signals were also detected in apoptotic cells. In addition, LCs and SGs were separated from the testis of male rats and primary cells were treated with beta-EP; this increased the mRNA levels of MOR and was accompanied by acute cell apoptosis. Our findings provide a foundation for the further study of apoptosis in reproductive cells regulated by beta-EP and the MOR receptor.