Male/female comparison of morphine effect on food intake--relation to anorexia nervosa.

We have proposed that endogenous opioids play a critical role in the etiology of anorexia nervosa by mediating an auto-addiction. A biological predisposition may result from an atypical endogenous opioid system. Morphine activation of the system increases food intake in most species, including normal humans and rats, but decreases food intake in mice. The atypical opioid system in mice may be representative of that in anorexia nervosa patients, causing the biological predisposition. Anorexia nervosa is 10 times more prevalent in females than males. In the context of this auto-addiction opioid model, it was interesting to determine if the effects of morphine on food intake were markedly different between the two sexes. Full dose-response curves were done of the effects of morphine on food intake in males and females in both rats and mice, representing the typical and atypical responses, respectively. Differences between the sexes were not found to explain the marked prevalence of anorexia nervosa for females. The marked preference is probably at some other step.