Effects of antecedent prolonged exercise on subsequent counterregulatory responses to hypoglycemia

Abstract

In the present study the hypothesis tested was that prior exercise may blunt counterregulatory responses to subsequent hypoglycemia. Healthy subjects [15 females (f)/15 males (m), age 27 ± 1 yr, body mass index 22 ± 1 kg/m², hemoglobin A_Ic5.6 ± 0.5%] were studied during 2-day experiments. Day 1 involved either 90-min morning and afternoon cycle exercise at 50% maximal O₂uptake (V˙o_2 max) (priorEXE, n = 16, 8 m/8 f) or equivalent rest periods (priorREST, n = 14, 7 m/7 f). Day 2 consisted of a 2-h hypoglycemic clamp in all subjects. Endogenous glucose production (EGP) was measured using [3-³H]glucose. Muscle sympathetic nerve activity (MSNA) was measured using microneurography. Day 2 insulin (87 ± 6 μU/ml) and plasma glucose levels (54 ± 2 mg/dl) were equivalent after priorEXE and priorREST. Significant blunting ( P < 0.01) of day 2 norepinephrine (−30 ± 4%), epinephrine (−37 ± 6%), glucagon (−60 ± 4%), growth hormone (−61 ± 5%), pancreatic polypeptide (−47 ± 4%), and MSNA (−90 ± 8%) responses to hypoglycemia occurred after priorEXE vs. priorREST. EGP during day 2 hypoglycemia was also suppressed significantly ( P < 0.01) after priorEXE compared with priorREST. In summary, two bouts of exercise (90 min at 50%V˙o_2 max) significantly reduced glucagon, catecholamines, growth hormone, pancreatic polypeptide, and EGP responses to subsequent hypoglycemia. We conclude that, in normal humans, antecedent prolonged moderate exercise blunts neuroendocrine and metabolic counterregulatory responses to subsequent hypoglycemia.