HORMONAL AND METABOLIC ADJUSTMENTS DURING EXERCISE IN HYPOXIA OR NORMOXIA IN HIGHLAND NATIVES

In sea-level natives, exposure to hypoxia for a few weeks is character ized by an increased dependence on blood glucose and a decreased relia nce on lactate for energy metabolism during exercise. These metabolic adjustments have been attributed to behavioral changes in the sympatho adrenergic and pancreatic systems. The aim of this study was to test t he hypothesis of a reduced sympathoadrenergic activation and subsequen t metabolic changes when high-altitude natives are acutely exposed to normoxia. Young Andean natives performed incremental exercise to exhau stion during hypoxia (arterial PO2 55.1 +/- 1.1 Torr) or during acute normoxia (arterial PO2 78.7 +/- 1.7 Torr). As a whole, oxygen uptake w as increased in normoxia compared with hypoxia during graded exercise. This finding is not related to a decrease in anaerobic metabolism but rather is interpreted as a consequence of a shift in substrate utiliz ation during exercise (increased contribution of fat as assessed by a reduction in the respiratory exchange ratio). These metabolic changes are not accompanied by modifications of glucoregulatory hormones (cate cholamines, insulin, and glucagon). In particular, the exercise-induce d catecholamine secretion was similar in chronic hypoxia and acute nor moxia. As a consequence, blood lactate accumulation during incremental exercise was similar in both conditions. It is concluded that high-al titude natives do not display any sign of a greater sympathoadrenergic activation during chronic hypoxia and that the exercise-induced hormo nal changes remained unaffected by acute inhalation of a normoxic gas mixture.