EFFECTS OF ADMINISTRATION OF AN OPIOID ANTAGONIST ON SERUM LEVELS OF PROLACTIN AND TESTOSTERONE IN MALE RABBITS

The objective of the study was to evaluate the effect of low daily dos es of naloxone on serum testosterone and prolactin levels in male rabb its over 10 days of treatment. Six groups of New Zealand white male ra bbits were used: two for the testosterone assay, two for the prolactin assay and two control groups. Animals in the testosterone groups were injected with 10 or 100 mu g/kg/day doses of naloxone, and those in t he prolactin groups with 12.5 or 100 mu g/kg/day doses of naloxone. Co ntrol groups were injected with saline. Blood samples were taken from all rabbits at baseline, 90 minutes after administering naloxone and 1 , 2, 4, 7 and 10 days after starting the study. Blood samples were dra wn from the main ear artery. Serum testosterone and prolactin levels w ere measured by radioimmunoassay. The testosterone levels increased si gnificantly and progressively with both doses. Prolactin levels, at th e 12.5 mu g dose of naloxone, decreased significantly at 90 min and re mained stable during the study. Prolactin levels at the 100 mu g dose decreased progressively. Low doses of naloxone cause important effects on the opioid endogenous system with a consecutive rise in testostero ne and a decrease in prolactin serum levels. Med Sci Res 26:511-512 (C ) 1998 Lippincott Williams & Wilkins.