Perifused fat cells.

In vitro methods currently utilized for the determination of lipolytic responses in adipose tissue have not allowed for the continuous monitoring of rapid successive changes in rates of lipolysis. The perifused fat cell system utilized in this investigation offers a simple, reproducible method by which minute-to-minute changes in the rate of lipolysis of isolated fat cells may be monitored. In this technique, isolated fat cells are placed in a plastic column and perifused with albumin-containing buffer in the absence and presence of various lipolytic agents. Using this technique, we have been able to observe alterations in the rates of glycerol release during the initiation of hormone-induced lipolysis. In addition, we have been able to observe the decline in glycerol release following the removal of the lipolytic hormone. In the perifused fat cell system, epinephrine, isoproterenol, and norepinephrine elicited a maximal lipolytic response at 10 pM, theophylline at 1 m&r, and glucagon at 5 PM. In addition, NG, 02’-dibutyryl cyclic adenosine 3’:5’-monophosphate (1 mM), adrenocorticotropic hormone (100 milliunits per ml), and thyroid stimulating hormone (75 milliunits per ml) effectively stimulated lipolysis in the perifused fat cell system, whereas cyclic adenosine 3’:5’-monophosphate (1 mM) and serotonin (1 II~M) were without effect. Unlike the incubated tissue method, growth hormone (20 pg per ml) was found to be a potent stimulator of lipolysis in this system. The combined administration of theophylline and epinephrine, both at submaximal concentrations, resulted in rates of glycerol release which were significantly greater than the sum of the rates observed during individual administration.