Defective Epinephrine and Growth Hormone Responses in Type I Diabetes Are Stimulus Specific

The counter regulatory hormone responses to hypoglycemia and a non-glucose stimulus, exercise, were evaluated in 18 subjects with type I diabetes and in 9 normal controls. Subjects with diabetes had no overt neuropathy, with R-R variations and postural plasma norepinephrine increments that were similar to those of controls. The diabetic subjects exhibited normal increments in plasma growth hormone (GH), norepinephrine, and cortisol but blunted or absent responses in plasma epinephrine and glucagon when hypoglycemia was severe (<40 mg/dl). During a 60-min clamped reduction in plasma glucose at ∼65 mg/dl, plasma GH and epinephrine increased 6- to 15-fold in controls but 2- to 4-fold in diabetics (P < .05). However, when subjects were exercised at this plasma glucose level (50 W for 10 min), plasma epinephrine and GH in diabetics rose markedly by 150–400% to attain the peaks reached by the controls. Plasma norepinephrine and cortisol increased to similar levels in both groups, and plasma glucagon was not significantly changed. We conclude that epinephrine and GH secretion in response to hypoglycemia are reduced in type I diabetes but that these defects are stimulus specific because the responses to exercise are not reduced.