The isolated fat cell perifusion (p-IFC) system is used to assess dynamic aspects of fat metabolism. The system is particularly well-suited to study "initiation" and "termination" of lipolysis. Glycerol release bay be initiated with epinephrine (EPI) and terminated passively by "buffer alone" or actively by insulin (INS). Perifusion with "high" or "low" INS was performed prior to, simultaneous with, or after infusion of EPI. Data obtained from such experiments reveal that both hormone concentration and the sequence of hormone administration greatly alter the responsiveness of adipose tissue to both lipolytic and antilipolytic stimuli. Furthermore, non-hormonal agents such as the nucleoside, adenosine, appears to play a modulating role, inhibiting lipolysis and altering the responsiveness of isolated fat cells to lipolytic stimuli. BIBLIOGRAPHIC REFERENCES: Solomon, S.S., Palazzolo, M. And King, L.E. Jr. Mechanism of Insulin Action: Specific Effects on Cyclic Nucleotide Phosphodiesterase Activity. Clin. Res. 23:501A, 1975. (ABS). Turpin, B.P., Duckworth, W.C. and Solomon, S.S. Modulation of Lipolysis by Adenosine in Perifusion System. Clin. Res. 24:30A, 1976. (ABS).