Naltrexone treatment produces dose-related effects on food and water intake but daily alcohol consumption is not affected

Abstract

There is evidence that naltrexone, an opioid antagonist, affects alcohol and food consumption. Though food intake is inherently involved when naltrexone effects on alcohol consumption have been studied, the differential effect of this opioid antagonist on both food and alcohol intake has not yet been reported. The present study analyzed the effect of a single daily dose of naltrexone on alcohol, food and water intake when these substances were available on a continuous basis. Wistar male rats were treated with s.c. injections of either naltrexone (2 or 10 mg/kg/day/rat) or a saline solution, 0.2 ml/day/rat for 7 days. This period was followed by a lapse of 7 days with no treatment (PT period), and this sequence of naltrexone or saline treatment followed by a period without treatment was repeated four times. Neither 2 mg/kg nor 10 mg/kg of naltrexone affected alcohol consumption, though the higher dose of naltrexone (10 mg/kg) increased food intake with respect to both the PT periods and the saline group and decreased water consumption with respect to the corresponding PT periods. Naltrexone at 2 mg/kg produced a decrease in food intake but only with respect to the PT periods. These results suggest that the effects of a single dose of naltrexone on alcohol consumption may not be evident when 24-h access to alcohol is assessed; however, naltrexone may produce different dose-related effects on food and water intake, suggesting that they may be mediated by distinct opioid system mechanisms.