Possible Function of Testicular Opioid Peptides in the Control of Testicular Function

Summary

In order to study the possible role of testicular opioids in the control of testicular functions, opioid antagonists were injected intratesticularly. Local administration of naloxone or nalmefene at 5 days of age increased the weight of the treated testis, and facilitated compensatory testicular hypertrophy. Treatment of hemicastrated rats with opioid receptor antagonists was also associated with a marked rise in production of the specific Sertoli cell androgen binding protein. In hemicastrated neonatal animals intratesticular administration of opioid antagonists or injection of anti-β-endorphin antiserum resulted in a decrease in basal testosterone secretion in vitro. In adult hemicastrated rats, intratesticular injection of opioid receptor antagonists decreased serum testosterone levels, basal testosterone secretion in vitro, and the response of testes to hCG. Treatment of the remaining testis with anti-β-endorphin antiserum inhibited testosterone production of the treated testis. These data indicate that testicular opioid peptides inhibit Sertoli cell function in neonatal animals by a paracrine mechanism. The result also suggests that β-endorphin, both in neonatal and adult rats, may function as autocrine modulator of Leydig cells, facilitating testosterone secretion.