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.
Key words
Insulin - Norepinephrine - Lipolysis - Fat Cells - Cyclic AMP - Adenyl Cyclase - Phosphodiesterase
1 NIH Post Doctoral Fellow.
Present address: Pharmakologisches Institut, Universität Bonn, D-53 Bonn, Germany,
Reuterstrasse 2b.
2 Present address: Imperial Chemical Industries Ltd., Pharmaceuticals Division, Alderley
Park, Macclesfield, Cheshire SK10 4TG, England.
