Suppression of counterregulatory hormone response to hypoglycemia by insulin per se

Although assessment of counterregulatory hormone responses to hypoglycemia relies upon insulin to lower the glucose level, it is not known if the exogenous insulin dose used itself influences the magnitude of the hormone response. To assess this, 12 normal subjects randomly received 2 hypoglycemic clamp studies in which the only variable was the insulin dose (0.6 or 5.0 mU/kg-min). Despite 10-fold differences in circulating insulin (265±29 vs 2576±222 pmol/L respectively), the hypoglycemic stimulus did not vary. Glucose levels fell over one hour, and then were maintained for two hours at the same hypoglycemic plateau (approximately 3.1 mmol/L for each study) by a variable glucose infusion. Although basal counterregulatory hormone levels in low and high dose studies were indistinguishable, during hypoglycemia the response of epinephrine, growth hormone, and glucagon was significantly suppressed when the degree of hyperinsulinemia was increased. We conclude that raising the magnitude of hyperinsulinemia suppresses the magnitude of the counterregulatory hormone response to hypoglycemia in normal subjects. This modulating effect of insulin per se is yet another variable in the interpretation of hypoglycemic counterregulation.