Cyclic estradiol treatment enhances the effects of interleukin-1beta on food intake in female rats.

Proinflammatory cytokines elicit behavioral and physiological responses that include decreased food intake, fever, and a general disinterest in usual activities. Ovarian hormones modulate immune system activity and responsiveness to cytokines in female mammals, suggesting that sex differences in immune function may be influenced by gonadal steroids. In this experiment, female adult rats were ovariectomized and given two daily subcutaneous injections of 5.0 or 20.0 microg of estradiol benzoate or the oil vehicle 3 weeks after surgery. Following 2 days of hormone treatment, animals received ip injections of interleukin-1beta (IL-1beta) or saline 1 h before light offset. Food and water intake was measured 2 h after light offset. The results indicate that a cyclic pattern of estradiol treatment enhances the anorectic effect of IL-1beta and suggest that responses to immune system activation are influenced by estradiol.