Effects of a Chronic Ethanol Diet on Sexual Behavior of Male Rats

Alcohol use is commonly believed to induce sexual dysfunction. To examine the nature and degree of sexual dysfunction induced by chronic alcohol consumption, we studied the effects of a liquid diet containing six percent ethanol on the copulatory behavior of sexually vigorous male Long-Evans rats. Control rats were pair-fed an isocaloric liquid diet and an additional group received normal food ad libitum. The groups were formed so that no differences in intromission latency, ejaculation frequency (number of ejaculations in the 60 minutes following the first intromission) or body weight were evident. Liquid food was administered once a day. The rats receiving alcohol drank throughout the course of the day. In contrast, the isocaloric controls consumed most of the available food within hours of its availability. Average daily intake of liquid diet was variable from 67 to 97 ml/rat per day. Copulatory behavior tests were administered weekly, beginning four days after initiation of the diet. No decrements in motivational aspects of copulatory behavior were evident in tests from four to 74 days after initiation of the study. In tests from four to 60 days after the start of alcohol exposure, there were no significant differences in any parameters of copulatory behavior. However, in tests administered after 67 days of alcohol exposure, the alcohol-treated rats demonstrated alterations in performance aspects of copulation: there was an increase in the number of mounts without intromission (mount frequency); an increase in the number of intromissions preceding ejaculation (intromission frequency); a decrease in copulatory efficacy; and an increase in the postejaculatory interval. In tests 74 and 81 days after the start of alcohol exposure, similar increases in mount frequency and postejaculatory interval were observed. Further, we observed a decrease in intromission frequency (premature ejaculation) coupled with a more dramatic decrease in copulatory efficacy. To ascertain whether the decreased copulatory efficacy and increased mount frequency were due to erectile dysfunction, we administered an ex copula penile reflex test 78 to 79 days after starting the ethanol diet and observed a profound deficit in erectile function. In contrast to these indications of reduced copulatory ability, the number of ejaculations obtained during the one-hour test period was not significantly decreased in alcohol-treated rats. Indirect assessment of systolic blood pressure 79 to 80 days after initiation of dietary manipulation revealed a moderate degree of hypertension in the alcohol-exposed rats. Rats were sacrificed 84 days after initiating the study. Despite isocaloric intakes, the nonalcoholic rats weighed 121 percent of their pretreatment body weight, compared to 105 percent for alcoholic rats. Ad lib chow-fed rats weighed 142 percent of their prestudy body weights. Indices of gonadal function (testes and accessory organ weights) do not indicate gonadal failure. Hormonal and neurochemical analyses will be performed. These data indicate that exposure to six percent alcohol for 12 weeks is not associated with overt gonadal or copulatory failure, although decrements in erectile ability, alterations in parameters of copulatory behavior, and a moderate degree of hypertension are observed. (Supported by NIH GM 08037, HL 02482, GM 04564, and NSF HRD 9106096)