Influence of trypsin on lipolysis in human fat cells. Comparison with rat adipocytes.

1. Trypsin-treated human and rat fat cells were obtained by digestion of adipose tissue with collagenase plus trypsin and their lipolytic response to insulin, catecholamines and dibutyryl cyclic AMP were compared with the lipolytic response of human and rat fat cells isolated with collagenase only. 2. In both human and rat fat cells, no significant modification occurred in the intracellular lactate dehydrogenase content and in the basal release of glycerol after trypsination. 3. In rat fat cells, trypsin abolished the antilipolytic effect of insulin but maintained a normal lipolytic response to epinephrine, norepinephrine and isoproterenol. 4. In human fat cells, on the contrary, trypsin failed to modify the antilipolytic effect of insulin, but markedly potentiated the lipolytic response to epinephrine, norepinephrine and isoproterenol. Trypsin also increased the rate of intracellular 3' :5' cyclic AMP accumulation in response to catecholamines. Under these conditions, however, trypsin-treated human fat cells had a normal reponse to the lipolytic agent dibutyryl cyclin AMP. 5. These data suggest that human fat cells differ from the rat ones by the existence in human adipocyte membranes of a trypsin-sensitive component which inhibits the catecholamine induced lipolytic process and which is different from the alpha receptors.