Relationship between plasma concentrations of immunoreactive beta-endorphin and food intake in rats

Periods of increased food intake in male rats were characterized by significant elevations in the plasma concentrations of immunoreactive beta-endorphin (beta-ep). Administration of 2-deoxy-D-glucose (400 mg/kg) produced rapid and concurrent increases in both food intake and plasma beta-ep. Administration of insulin (10 units/kg) produced large delayed increases in food intake but only modest delayed increases in plasma beta-ep. Spontaneous nocturnal feeding was associated with increased plasma beta-ep. Increases in daytime food intake in rats subjected to 24 hr of food deprivation were also characterized by elevated plasma beta-ep. In all cases examined, those feeding behaviors in male rats which were subject to inhibition by naloxone were characterized by elevated concentration of plasma beta-ep.