The effect of phenformin on amino acid-induced insulin secretion in diabetics

Twenty-one patients with mild maturity-onset diabetes were given introduodenal infusions of an amino acid mixture (0.5 g amino acids per kg body weight). In 9 other patients L-arginine was infused intravenously in a constant dose of 25 g. Alpha-amino nitrogen, blood glucose and plasma insulin levels were assayed under control conditions and after three days of treatment with phenformin, 150 mg daily, plus the same 150 mg dose 60 min before the second loading. Intraduodenal infusion of the amino acid mixture provoked a greater increase in plasma insulin than intravenous infusion of L-arginine, this increase being significantly inhibited by phenformin only in the first case. Since no evident influence of phenformin on the intestinal absorption of amino acids could be demonstrated, this effect may be explained by a local action on the intestinal wall exposed to high concentrations of the drug, resulting in the inhibition of the insulin secretion stimulating activity of the gut.