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Norepinephrine Infusion during Moderate-Intensity Exercise Increases Glucose Production and Uptake¹

McGill Nutrition and Food Science Centre (S.H.K., N.A.M., E.B.M.), Royal Victoria, Montréal, Québec, Canada, H3A 1A1; The Department of Internal Medicine and Institute of Gerontology (J.B.H.), University of Michigan and Veterans Affairs Medical Centre, Ann Arbor, Michigan, 48109; and The Departments of Physiology and Medicine (M.V.), University of Toronto, Toronto, Ontario, Canada, M5S 1A8

Address all correspondence and requests for reprints to: Errol B Marliss, McGill Nutrition and Food Science Centre, Royal Victoria Hospital, 687 Pine Avenue West, Montréal, Québec, Canada H3A 1A1. E-mail: errol.marliss{at}muhc.mcgill.ca

A role for the increase in circulating norepinephrine (NE) during intense exercise [IE; 80% maximum O₂ uptake (O_2max)] in the marked increment in glucose rate of production (Ra) during IE is hypothesized. Seven fit male subjects (27 ± 2 yr old; body mass index, 23 ± 1 kg/m²; O_2max, 63 ± 5 mL/kg·min) underwent 40 min of postabsorptive moderate-intensity (53% O_2max) cycle ergometer exercise (126 ± 14 W), once without [control (CON)] and once with NE infusion (0.1 µg/kg·min) from 30–40 min (NE). With infusion, plasma NE reached 15.9 ± 1.0 nM (8-fold rest, 2-fold CON). Ra doubled to 4.40 ± 0.44 in CON, but rose to 7.55 ± 0.68 mg/kg·min with NE infusion (P = 0.003). Ra correlated strongly (r² = 0.92, P < 0.02) with plasma NE during and immediately after infusion. With NE infusion, peak glucose uptake [rate of disappearance (Rd), 6.57 ± 0.59 vs. 4.53 ± 0.55 mg/kg·min, P < 0.02] and glucose metabolic clearance rate (P < 0.05) were higher than in CON. Glycemia rose minimally during the NE infusion but did not differ between groups at any time during exercise. Glucagon-to-insulin ratio increased minimally, and epinephrine increased approximately 2.5- to 3-fold at peak but did not differ between groups. Thus, NE infusion during moderate exercise led to increments in Ra and Rd in fit individuals, supporting a possible contributory role for the increase of plasma NE in IE. NE effects on Rd and metabolic clearance rate during exercise may differ from its effects at rest.

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