EFFECT OF NALOXONE ON SERUM PROLACTIN LEVELS IN ADULT MALE RABBITS

In order to clarify the possible physiological role of endogenous opio id peptides (EOP), we studied the effect of low doses of naloxone (spe cific opiate antagonist) on plasma prolactin levels in male rabbits. F ive groups of five male rabbits each was injected daily between 8-9 a. m., with naloxone 12.5, 25, 50, 100 and 200 mu g/kg/day. An additional group of ten animals was injected with saline solution and considered the control group. Blood samples were taken at baseline before naloxo ne administration and later at 90 min and 1, 2, 4, 7, 10 days after it s administration. Samples were also taken 4 days after stopping naloxo ne administration (day 14). Plasma prolactin levels were measured by R IA. A significant constant decrease in PRL levels was seen with the 12 .5 mu g at 90 minutes, while with the remaining doses a progressive de crease was recorded throughout the study.