Loss of Potentiating Effect of Hypoglycemia on the Glucagon Response to Hyperaminoacidemia in IDDM

IDDM subjects lose the ability to release glucagon during hypoglycemia. Because replacement of basal levels of amino acids enhances the glucagon response to hypoglycemia in healthy subjects, we tested whether raising amino acid levels during hypoglycemia could reverse the defective α-cell response in IDDM patients. For this purpose, 11 IDDM patients (HbA₁ 9.4 ± 0.6%) and 8 healthy, nondiabetic subjects received two hypoglycemic insulin clamp studies (0.8 mU.kg⁻¹ · min⁻¹) in which plasma glucose was clamped at 55 mg/dl (3.08 mM) for 180 min. During one of the studies, an infusion of amino acids was superimposed between 120 and 180 min (0.3 g.kg⁻¹ · h−1). This dose of amino acids had a small effect on plasma glucagon levels during euglycemic hyperinsulinemia that was comparable in normal and IDDM subjects. In healthy control subjects, plasma glucagon rose by 80% during the initial hypoglycemic phase of the study. The addition of amino acids produced a further sharp (200–250 ng/L, P < 0.02) rise in plasma glucagon, such a change did not occur in the absence of amino acids. In contrast, plasma glucagon in IDDM patients failed to increase during hypoglycemia alone and rose by only 40–50 ng/L (P < 0.05 vs. controls) when amino acid infusion was superimposed, even though plasma amino acid levels rose to the same extent in IDDM and control subjects. More importantly, the rise in glucagon produced by amino acids was comparable during hypoglycemic and euglycemic hyperinsulinemia in the IDDM patients, results strikingly different from those observed in nondiabetic control subjects. We conclude that hypoglycemia greatly amplifies the α-cell response to hyperaminoacidemia in healthy subjects but not in IDDM.