The effect of naloxone on plasma concentrations of testosterone in male goats

The purpose of this work was to study the effect of the chronic administration of low doses of naloxone (0.5 mg/12 h/15 days) on plasma levels of testosterone in the anoestrus male goat. It was observed that during the first seven days of treatment, testosterone levels did not change. Thereafter, concentrations of testosterone increased to 7.5 +/- 0.3 ng/ml at the end of treatment. Following drug withdrawal, testosterone levels returned slowly to control values. It was concluded that the opioid antagonist, naloxone, administered in low doses, is capable of modifying testosterone concentrations in plasma, thereby giving further support that endogenous opioids are modulators of the reproductive function in goats. (C) 1998 Elsevier Science B.V.