Effects of Differing Antecedent Hypoglycemia on Subsequent Counterregulation in Normal Humans

The aim of the study was to determine the effects of specific levels of antecedent hypoglycemia on subsequent autonomic, neuroendocrine, and metabolic counter-regulatory responses. Eight healthy, overnight-fasted male subjects were studied during 2-day protocols on four separate randomized occasions separated by at least 2 months. On day 1, insulin was infused at a rate of 9 pmol · kg⁻¹ · min⁻¹ and 2-h clamped euglycemia (plasma glucose 5.2 ± 0.2 mmol/l) or differing hypoglycemia (plasma glucose 3.9 ± 0.1, 3.3 ± 0.1, or 2.9 ± 0.1 mmol/l) was obtained during morning and afternoon. The next morning after an evening meal and 10-h overnight fast, each subject underwent a 2-h hyperin-sulinemic (9 pmol · kg⁻¹ · min⁻¹) hypoglycemic (2.9 ± 0.1 mmol/l) clamp study. Despite equivalent day 2 plasma glucose and insulin levels, differing levels of antecedent hypoglycemia produced specific blunting of subsequent counterregulatory responses. Day 1 hypoglycemia of 3.9 mmol/l resulted in significantly (P < 0.01) blunted epinephrine, muscle sympathetic nerve activity, and glucagon responses. Day 1 hypoglycemia of 3.3 mmol/l resulted in additional significant blunting (P < 0.01) of pancreatic polypeptide, norepinephrine, growth hormone, endogenous glucose production, and lipolytic responses. Deeper day 1 hypoglycemia of 2.9 mmol/l produced similar day 2 counterregulatory failure as day 1 hypoglycemia of 3.3 mmol/l. In summary, in healthy overnight-fasted men, mild antecedent hypoglycemia of 3.9 mmol/l significantly blunts sympathoadrenal and glucagon, but not other forms of neuroendocrine counterregulatory responses, to subsequent hypoglycemia. Antecedent hypoglycemia of 3.3 mmol/l resulted in additional significant blunting of all major neuroendocrine and metabolic responses to subsequent hypoglycemia. We conclude that in normal humans, there is a hierarchy of blunted counterregulatory responses that are determined by the depth of antecedent hypoglycemia.