Effects of antecedent prolonged exercise on subsequent counterregulatory responses to hypoglycemia

In the present study the hypothesis tested was that prior exercise may blun t counterregulatory responses to subsequent hypoglycemia. Healthy subjects [15 females (f)/15 males (m), age 27 +/- 1 yr, body mass index 22 +/- 1 kg/ m(2), hemoglobin A(Ic) 5.6 +/- 0.5%] were studied during 2-day experiments. Day 1 involved either 90-min morning and afternoon cycle exercise at 50% m aximal O-2 uptake ((V) over dot O-2 max) (priorEXE, n = 16, 8 m/8 f) or equ ivalent 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) wa s measured using [3-H-3]glucose. Muscle sympathetic nerve activity (MSNA) w as measured using microneurography. Day 2 insulin (87 +/- 6 muU/ml) and pla sma glucose levels (54 +/- 2 mg/dl) were equivalent after priorEXE and prio rREST. 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 t o hypoglycemia occurred after priorEXE vs. priorREST. EGP during day 2 hypo glycemia was also suppressed significantly (P < 0.01) after priorEXE compar ed with priorREST. In summary, two bouts of exercise (90 min at 50% (V) ove r dot O-2 max) significantly reduced glucagon, cat echolamines, growth horm one, 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 subseque nt hypoglycemia.