Effects of Insulin on the Lipolytic System of Rat Fat Cells

Authors:
  • PSP. S. Schönhöfer
    P. S. Schönhöfer
  • ISI. F. Skidmore
    I. F. Skidmore
  • GKG. Krishna
    G. Krishna
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Abstract
At concentrations ranging between 10 µ units and 10 m units/ml insulin inhibits lipolysis stimulated by sub-optimal concentrations of norepinephrine or theophylline. At supraoptimal concentrations of the stimulating agent no effect of insulin can be detected. Adenyl cyclase activity in homogenates of fat cells stimulated with norepinephrine or sodium fluoride is not influenced by insulin even when the cells are preincubated with the antilipolytic agent. No change in phosphodiesterase activity is found under these conditions. With cells prelabelled with tritiated adenine it was shown that insulin had no effect on the initial rate of accumulation of radiolabeled cyclic AMP but that accumulation stopped and declined earlier and more rapidly than when insulin was absent. This effect of insulin was most marked at low concentrations of norepinephrine and was independent of preincubation of the cells with insulin before stimulation with norepinephrine.