Observations on the lipolytic action in vitro of a fat-mobilizing substance extracted from urine of fasting rats.

Abstract

An investigation has been carried out of factors in the lipolytic response of adipose tissue to a fat-mobilizing substance (FMS IB) extracted from the urine of fasting rats. Response was increased when rats were exposed to cold prior to removal of adipose tissue and was decreased in adipose tissue of rats rendered hyperphagic and obese by bilateral electrolytic ablation of the ventromedial region of the hypothalamus. These observations in vitro are consistent with observations on fat catabolism or storage in vivo after cold exposure and in hypothalamic hyperphagia.Previous feeding of a high-protein diet inhibited lipolytic response in vitro of adipose tissue to both FMS IB and adrenaline; previous feeding of a noncarbohydrate high-fat diet also inhibited lipolytic response to FMS IB but not to adrenaline. Of the adipose tissues tested, lipolytic response to FMS IB was in the order epididymal > perinephric > omentum. There was no sex difference in the response of adipose tissue; the response of adipose tissue of the young male rat was considerably less than that of the adult male rat. Adipose tissue of fasted rats was much more responsive to FMS IB than was that of fed rats. This response could be almost completely abolished by the addition of glucose (180 mg/100 ml) to the incubating medium; lesser concentrations of glucose had a smaller inhibitory effect. A linear lipolytic response of adipose tissue to increasing amounts of FMS IB has been demonstrated.