Amino-Terminal Peptide of Growth Hormone Enhances Insulin Action in Normal Rats

Earlier studies demonstrated that the 20K-dalton variant of human GH (hGH), which differs from hGH by deletion of the amino acid residues 32–46, has decreased insulinlike activity. The current study assessed whether a peptide representing this deleted region could enhance insulin-stimulated glucose uptake in the intact rat and if this effect was localized in liver and/or muscle. Peptides hGH-(32–46) and rat GH-(32–45) were used in these studies. Assessment of the action of a peptide was done by determining its effect on the steady state serum glucose (SSSG) concentration during an insulin suppression test. Glucose was infused alone and with two rates of infusion of insulin. The data indicated that neither of the GH peptides affected SSSG in the absence of exogenously administered insulin or at low (40 μU/ml) serum levels of insulin, but when serum insulin was increased to 77 μU/ml, a significant (P < 0.05) decrease in SSSG was produced by the peptides. In subsequent studies isolated liver and hind limb sk...