Parallel insulin-like actions of human growth hormone and its part sequence hGH 7–13

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Abstract
The insulin-like effects of human growth hormone [hGH] and the synthetic part sequence, N.alpha.-acetyl-hGH 7-13, on glycogen synthase and phosphorylase were compared in an in vivo system during 16- to 18-day-old rats. Both the hormone and its part sequences had similar effects, increasing muscle glycogen synthase a activity and decreasing liver phosphorylase a activity, without affecting phosphorylase activity in muscle or synthase activity in liver. Insulin had similar effects, but also increased liver synthase a activity. The effects of all 3 substances could be abolished by prior treatment of the animals with anti-insulin serum, showing that the effects of GH and its part sequences were insulin-dependent. Both GH and the synthetic peptide increased the binding of insulin to liver plasma membrane. Apparently, the insulin-like activity of hGH is associated with a region containing residues 7 to 13 of the hormone molecule, and this activity is insulin-dependent. It is suggested that both GH and the synthetic peptide produce insulin-like activity by enhancing the binding of circulating insulin to its receptor.