The Insulin-Like Action of β-Cell-Tropin on Glucose and Lipid Metabolism in Adipocytes

Summary

The insulin-like activity of the pituitary pars-intermedia insulin secretagogue β-cell-tropin, ACTH_22-39, has been studied on rat adipocytes. The peptide was prepared by tryptic digestion of synthetic human CLIP, ACTH_18-39. β-Cell-tropin stimulated the incorporation of ³H₂O into total lipids. The 50% maximal activity concentration was 5 × 10^-2 ng/ml^-1 about 2.G5 × 10^-11 M. lodination of tyrosine, the penultimate amino-acid of the N-terminal, eliminated lipogenic activity, and acetylation of the N-terminal valine reduced activity. ACTH and CLIP (ACTH_18-39) had no lipogenic action on the adipocyte system studied. β-Cell-tropin stimulated the oxidation of glucose and the conversion of glucose into saponified fatty acids and glyceride glycerol. The influence of β-cell-tropin and insulin on the incorporation of glucose into total lipids, saponified fatty acids and glyceride glycerol was not additive. The results suggest that β-cell-tropin is either a potent lipogenic hormone, stimulating the conversion of glucose into lipids or that it activates endogenous insulin. The biological activity is associated with the N-terminal amino-acids of the peptide. The possible significance of β-cell-tropin in obesity is discussed.

Key-Words:

Insulin Secretagogue - β-Cell-Tropin - Lipid Metabolism - Adipocytes - Obesity - Obese Mice