Influence of adipocyte isolation by collagenase on phosphodiesterase activity and lipolysis in man

The maximum phosphodiesterase activity (Vmax) with low and high Km was, respectively, 10- and 3-times greater in tissue fragments than in collagenase-isolated adipocytes obtained from subcutaneous fat layers in man. The exposure of such tissue fragments to collagenase of various origins in order to isolate the fat cells resulted in a 60-70% inhibition of phosphodiesterase (PDE) activity. Noradrenaline- and isopropyl noradrenaline-induced rates of lipolysis were more rapid in the isolated fat cells than in the tissue fragments. The sensitivity to catecholamines, however, was the same for the two tissue preparations. Nor did they differ in respect to the effect of theophylline, a PDE inhibitor, on the rate of lipolysis. The time curve for cyclic AMP accumulation was significantly higher in the isolated adipocytes than in tissue fragments in the presence of isopropyl noradrenaline. It is concluded that the greater lipolytic response of collagenase-isolated adipocytes than of tissue fragments to catecholamines may be attributed, at least in some measure, to the higher concentration of cyclic AMP resulting from a decrease in PDE activity.