Augmented lipolysis in rat adipose tissue upon repeated exposure to epinephrine

A perfusion system was used to investigate the lipolytic response to epinephrine of minced epididymal fat pads from fed and 24-hr fasted rats. Epinephrine was infused at a final concentration of 1 X 10(-6) M for 60-min periods. Basal glycerol release from tissue and cells of fed animals was 3 mumoles/min/ml of sample. Epinephrine stimulated lipolysis 20-fold in tissue pieces. There was an additional two-fold increase during a repeated epinephrine infusion after 30 min with buffer alone. In contrast, tissue from fasted rats showed no difference upon successive infusions of epinephrine. Isolated cells of fed and fasted animals also produced peaks of equal magnitude on both exposures to epinephrine. Preincubation of fed tissue with anti-insulin serum did not abolish the augmented response to the hormone. Preincubation of the fed tissue for 90 min with omission of the first epinephrine exposure did not produce an augmented response. It is concluded that exposure of adipose tissue to 1 X 10(-6)M epinephrine will produce augmented stimulation of lipolysis on a second exposure. Fasting and isolation of cells abolishes the augmented response by a mechanism which does not involve removal of insulin from the fat cell.