Physiologic concentrations of beta-lipotropin stimulate lipolysis in rabbit adipocytes

The proopiocorticomelanotropin (POMC) sequence beta-lipotropin stimulates glycerol release from incubated rabbit adipocytes at a minimal concentration of 10(-9) mol/L. However, when lipolysis inhibiting substances (eg, fatty acids and adenosine) and contaminating peptide degrading activity are continuously removed by fat cell perifusion, the sensitivity is increased to 10(-13) and partly to 10(-14) mol/L beta-lipotropin. This higher sensitivity of the perifused adipocyte could also be demonstrated with alpha-MSH (from 5 X 10(-10) to 10(-13) mol/L). The restimulation of glycerol release was shown for both peptides. We conclude that POMC peptides might be involved in the regulation of lipolysis since the minimal effective concentrations are near to plasma concentrations.