Epinephrine infusion during moderate intensity exercise increases glucose production and uptake

Abstract

The glucoregulatory response to intense exercise [IE, >80% maximum O2 uptake (V˙o 2 max)] comprises a marked increment in glucose production (Ra) and a lesser increment in glucose uptake (Rd), resulting in hyperglycemia. The Ra correlates with plasma catecholamines but not with the glucagon-to-insulin (IRG/IRI) ratio. If epinephrine (Epi) infusion during moderate exercise were able to markedly stimulate Ra, this would support an important role for the catecholamines' response in IE. Seven fit male subjects (26 ± 2 yr, body mass index 23 ± 0.5 kg/m2,V˙o 2 max 65 ± 5 ml ⋅ kg− 1 ⋅ min− 1) underwent 40 min of postabsorptive cycle ergometer exercise (145 ± 14 W) once without [control (CON)] and once with Epi infusion [EPI (0.1 μg ⋅ kg− 1 ⋅ min− 1)] from 30 to 40 min. Epi levels reached 9.4 ± 0.8 nM (20× rest, 10× CON). Ra increased ∼70% to 3.75 ± 0.53 in CON but to 8.57 ± 0.58 mg ⋅ kg− 1 ⋅ min− 1in EPI ( P < 0.001). Increments in Ra and Epi correlated ( r 2 = 0.923, P ≤ 0.01). In EPI, peak Rd (5.55 ± 0.54 vs. 3.38 ± 0.46 mg ⋅ kg− 1 ⋅ min− 1, P = 0.006) and glucose metabolic clearance rate (MCR, P= 0.018) were higher. The Ra-to-Rdimbalance in EPI caused hyperglycemia (7.12 ± 0.22 vs. 5.59 ± 0.22 mM, P = 0.001) until minute 60 of recovery. A small and late IRG/IRI increase ( P = 0.015 vs. CON) could not account for the Ra increase. Norepinephrine (∼4× increase at peak) did not differ between EPI and CON. Thus Epi infusion during moderate exercise led to increments in Ra and Rd and caused rises of plasma glucose, lactate, and respiratory exchange ratio in fit individuals, supporting a regulatory role for Epi in IE. Epi's effects on Rd and MCR during exercise may differ from its effects at rest.