Sex and hormone dependent alterations in responsiveness to caloric dilution

Potential sex differences in the long-term control of feeding behavior in rats was tested by comparing male and female rats in terms of their responsiveness to a 20 and 40 percent diet dilution challenge. During three-day test periods with both levels of diet dilution, female rats increased their daily food intake (FI) significantly more than did male rats. As a further index of greater precision in the long-term control of feeding behavior by female than by male rats, body weight (BWt) was less affected in female than in male rats during the caloric dilution challenges. In a second experiment, gonadectomy was found to attenuate this sexually dimorphic response to a 40% diet dilution test, whereas daily injections of gonadal hormones reestablished the sex difference in FI and BWt changes produced by the dilution challenge. Since responsiveness to the dilution challenge of female rats, but not males, was altered by gonadectomy and steroid treatment, it appears that estrogen shifts the control of feeding behavior in female rats towards more long-term factors.