Central infusion of interleukin-I receptor antagonist fails to alter feeding and weight gain

Interleukin-I (IL-I) administered either i.p. or i.c.v. provokes sickness behaviors, including suppression of feeding. As well, the possibility exists that IL-I contributes to the cascade of factors that regulate feeding under basal conditions. The current study assessed the contribution of IL-I in the control of food intake and body weight under physiological conditions in male rats. Pretreatment with an IL-I receptor antagonist (IL-Ira, 16 mg/kg, i.p.) completely blocked the suppression of food intake produced by injection of IL-1β (4 μg/kg, i.p.). However, neither daily injections of IL-Ira (16 mg/kg, i.p.) for 4 consecutive days nor infusion of IL-Ira (500 μg/day, i.c.v.) for 7 days altered daily food intake and the rate of body weight gain. These findings suggest while IL-I may play a role in anorexia associated with sickness, this cytokine likely does not play a physiological role in the regulation of daily food intake and long-term energy balance. (C) 2000 Lippincott Williams and Wilkins.