Acute hypoxia reduces exogenous glucose oxidation, glucose turnover, and metabolic clearance rate during steady-state aerobic exercise.

Abstract

BACKGROUND\nExogenous carbohydrate oxidation is lower during steady-state aerobic exercise in native lowlanders sojourning at high altitude (HA) compared to sea level (SL). However, the underlying mechanism contributing to reduction in exogenous carbohydrate oxidation during steady-state aerobic exercise performed at HA have not been explored.\n\n\nOBJECTIVE\nTo determine if alterations in glucose rate of appearance (Ra), disappearance (Rd) and metabolic clearance rate (MCR) at HA provide a mechanism for explaining the observation of lower exogenous carbohydrate oxidation compared to during metabolically-matched, steady-state exercise at SL.\n\n\nMETHODS\nUsing a randomized, crossover design, native lowlanders (n\u202f=\u202f8 males, mean\u202f±\u202fSD, age: 23\u202f±\u202f2\u202fyr, body mass: 87\u202f±\u202f10\u202fkg, and VO2peak: SL 4.3\u202f±\u202f0.2\u202fL/min and HA 2.9\u202f±\u202f0.2\u202fL/min) consumed 145\u202fg (1.8\u202fg/min) of glucose while performing 80-min of metabolically-matched (SL: 1.66\u202f±\u202f0.14 V̇O2 L/min 329\u202f±\u202f28\u202fkcal, HA: 1.59\u202f±\u202f0.10 V̇O2 L/min, 320\u202f±\u202f19\u202fkcal) treadmill exercise in SL (757\u202fmmHg) and HA (460\u202fmmHg) conditions after a 5-h exposure. Substrate oxidation rates (g/min) and glucose turnover (mg/kg/min) during exercise were determined using indirect calorimetry and dual tracer technique (13C-glucose oral ingestion and [6,6-2H2]-glucose primed, continuous infusion).\n\n\nRESULTS\nTotal carbohydrate oxidation was higher (P\u202f<\u202f.05) at HA (2.15\u202f±\u202f0.32) compared to SL (1.39\u202f±\u202f0.14). Exogenous glucose oxidation rate was lower (P\u202f<\u202f.05) at HA (0.35\u202f±\u202f0.07) than SL (0.44\u202f±\u202f0.05). Muscle glycogen oxidation was higher at HA (1.67\u202f±\u202f0.26) compared to SL (0.83\u202f±\u202f0.13). Total glucose Ra was lower (P\u202f<\u202f.05) at HA (12.3\u202f±\u202f1.5) compared to SL (13.8\u202f±\u202f2.0). Exogenous glucose Ra was lower (P\u202f<\u202f.05) at HA (8.9\u202f±\u202f1.3) compared to SL (10.9\u202f±\u202f2.2). Glucose Rd was lower (P\u202f<\u202f.05) at HA (12.7\u202f±\u202f1.7) compared to SL (14.3\u202f±\u202f2.0). MCR was lower (P\u202f<\u202f.05) at HA (9.0\u202f±\u202f1.8) compared to SL (12.1\u202f±\u202f2.3). Circulating glucose and insulin concentrations were higher in response carbohydrate intake during exercise at HA compared to SL.\n\n\nCONCLUSION\nNovel results from this investigation suggest that reductions in exogenous carbohydrate oxidation at HA may be multifactorial; however, the apparent insensitivity of peripheral tissue to glucose uptake may be a primary determinate.