Fine-tuning control of testicular functions.

The effect of testicular administration of peptides synthesized in the testis (somatostatin, oxytocin) or peptide antagonists (opioid receptor antagonists naloxone, nalmefene, anti-corticotrop hormone-releasing hormone antiserum, beta-endorphin antiserum), partial denervation of the testis, and combination of local treatment with peptides/peptide antagonists and denervation was studied on testicular steroidogenesis in immature hemicastrated rats. The observations indicate that beta-endorphin, corticotrop hormone-releasing hormone, oxytocin, and somatostatin exert a stimulatory, whereas enkephalin has an inhibitory action on steroidogenesis. Surgical (vasectomy) or pharmacological (local injection of 6-hydroxydoparnine) denervation suppresses testosterone secretion. Following partial denervation of the testis the effect of naloxone or oxytocin on steroidogenesis observed in fully innervated gonad is not present or the effect is paradoxical. These results indicate that steroidogenesis is fine-tuned by local peptide actions, and neural inputs. Data further suggest an interaction between local peptide action and neural control.