Reversal of chronic ethanol-induced testosterone suppression in peripubertal male rats by opiate blockade.
Teenage drinking continues to be a significant problem in the U.S., as well as abroad. We have previously demonstrated that opiate blockade with naltrexone, a drug currently used in patients to diminish alcohol craving, prevented the fall in serum testosterone seen after acute ethanol (EtOH) exposure in young, peripubertal male rats. To follow-up on this reversal, a series of experiments was performed to determine if naltrexone would also prevent the testosterone suppression caused by chronic EtOH exposure. Peripubertal rats either 45 days old (mid-pubertal) or 55 days old (late pubertal) were fed an EtOH-containing liquid diet or pair-fed control diet for 14 days. Each animal was implanted with either a naltrexone containing or placebo pellet before starting the liquid diet. In each age group, EtOH alone significantly suppressed testosterone, whereas naltrexone prevented this fall, although it had no effect alone. Serum luteinizing hormone was also suppressed by EtOH; however, naltrexone did not abrogate this fall. In the 45-day-old animals, beta-luteinizing hormone mRNA levels rose significantly in the EtOH group, but not when naltrexone was coadministered with EtOH. There was no change in hypothalamic luteinizing hormone releasing hormone (LHRH) mRNA, pro-LHRH, or LHRH in any group at either age. Thus, naltrexone is able to partially prevent the EtOH-induced suppression of gonadal testosterone of young, adolescent male rats. This effect appears to be mediated directly at gonadal level, because hypothalamic and pituitary hormone changes were minor and nonsignificant.