LEPTIN PREVENTS POSTHIBERNATION WEIGHT-GAIN BUT DOES NOT REDUCE ENERGY-EXPENDITURE IN ARCTIC GROUND-SQUIRRELS

In mammals, leptin reduces energy intake and may increase energy expen diture as a means to maintain body weight and/or adiposity at an appro priate level. Hibernating mammals seasonally alter body mass, food int ake, and body composition and, therefore, represent an attractive mode l for investigating the physiological regulation of changing body mass and adiposity. Previous experiments in our laboratory demonstrated th at administration of mouse recombinant leptin reduces food intake and body weight in arctic ground squirrels during prehibernation fattening . In addition, leptin appeared to reduce metabolic efficiency (weight gain per unit of energy intake). This result suggests that reduced foo d intake alone may not account for the observed weight loss. Here, we describe the effect of a 3-week constant infusion of leptin given to p osthibernation arctic ground squirrels on food consumption and energy expenditure. Mouse recombinant leptin (1 mg/ml) was administered throu gh subcutaneously implanted mini-osmotic pumps (10 mu l/hr flow rate). Resting metabolic rate was monitored before and during the 3-week lep tin administration period by indirect calorimetry. Body temperature an d Locomotory activity were monitored continuously by abdominal radiotr ansmitters. At the end of the leptin administration period, thermogeni c capacity was evaluated by measuring brown fat uncoupling protein-1 m RNA and protein levels. Leptin administration resulted in reduced food intake and prevented posthibernation weight gain, but it did not alte r any of the measured parameters of energy expenditure. (C) 1997 Elsev ier Science Inc.