Pituitary polypeptide with hypoglycaemic action in diabetes mellitus

Identification of the aspartimide structure in a previously-reported peptide

The octapeptide Leu-Ser-Arg-Leu-Phe-Asp-Asn-Ala (hGH 6-13) has been reported to show insulin-potentiating properties, and its synthesis by conventional solid-phase synthesis was previously described. It is now shown that peptide synthesized with diisopropylethylamine or N-methylmorpholine as neutralizing base in each cycle does have the above structure. When triethylamine was used as neutralizing base however, the Asp residue was converted to its imide, the presence of which has been demonstrated by means of infrared, 1H-NMR and fast-atom bombardment mass spectra, and by reactivity studies, electrophoresis at several pH values, and enzymic hydrolysis. Only the imide form of the peptide possesses the previously reported biological properties. A study of imide formation from protected and unprotected peptides showed that cyclization occurred during a wide range of acid and base treatments, but 10% triethylamine in CH2Cl2 was most effective, producing over 40% of imide in 90 min. The results of the investigation are compared with others in the literature, including those for the peptide hormone secretin.

Tests for cataglykin activity on a cyanogen bromide fragment of human growth hormone

A peptide having the reputed essential amino acid sequence to show cataglykin-like effects was prepared from human growth hormone (hGH) by cyanogen bromide cleavage and was tested in two systems in which cataglykin has effects. The peptide prolonged the depression of blood glucose concentration brought about by insulin during intravenous insulin tolerance tests in rats. However, the magnitude of the depression caused by insulin was not increased. There was no stimulation by the peptide of glucose uptake by rat hemidiaphragrams in the presence of insulin in vitro. Thus, this peptide does not duplicate the effects of cataglykin.

Insulin antagonist of pituitary origin in plasma of normal and diabetic subjects

Studies on ultrafiltrates of the plasma of normal and diabetic subjects have shown that a polypeptide of similar characteristics to the growth-hormone-derived polypeptide In-G is present in higher concentrations in diabetic subjects, thus indicating a possible role in the pathogenesis of diabetes mellitus. The polypeptide is absent from the plasma of hypophysectomized diabetic patients.

Potentiation of insulin action in normal subjects by a pituitary polypeptide

A pituitary polypeptide, acceleratory polypeptide-growth hormone (ACG), has been found to increase the sensitivity of fasting normal people to intravenous insulin. It is suggested that diminished activity of this polypeptide-or increased activity of another polypeptide, inhibitory polypeptide-growth hormone (ING)-may have a role in the genesis of diabetes mellitus.