EFFECT OF NALOXONE ON SERUM TESTOSTERONE IN ADULT MALE RABBITS

Considerable evidence suggests that endogenous opioids may play an imp ortant role in the hypothalamic LH-releasing hormone. Administration o f high doses of naloxone, an opiate antagonist, produces an increase i n plasma concentration of LH. Naltrexone administration to healthy mal es produces an increase in both immunoactive and bioactive LH. The obj ective of the present work was to assess the effect of low doses of na loxone during 10 consecutive days on testosterone serum levels in rabb it. Three groups of five rabbits were injected with naloxone or saline . Naloxone was tested at 0.1 and 0.01 mg/kg day(-1). Blood samples wer e taken at 90 min and 1, 2, 4, 7, 10, and 14 days after starting nalox one administration. Plasma testosterone (T) levels were measured by RI A. T levels increased progressively through the study in the experimen tal groups. The differences were significant after days 4 and 7 for 0. 01-mg/kg and 0.1-mg/kg doses, respectively. T levels in both groups pe aked at day 10 and decreased at day 14 (4 days after treatment).