Relationship among Blood Lactate and Plasma Catecholamine Levels during Exercise in Acute Hypoxia

Abstract

Five male subjects performed steady exercise on a cycle ergometer at an intensity of 60% maximal 0₂ uptake (V0₂max) for 6 min on three separate occasions while breathing gas mixtures of 12, 16 or 21% 0₂ in N₂ Expired gas fractions, ventilation, heart rate, arterial 0₂ saturation (Sa0₂), blood lactate (La) and plasma catecholamines (epinephrine: E and norepinephrine: NE) were measured. 0₂ uptake (V0₂) was calculated for the last minute of exercise. Blood samples were drawn at rest and immediately after exercise. By inspiring hypoxic gas mixtures, the Sa0₂ value decreased during exercise to 85.0±5.4 (16%) and 66.4±4.1 (12%) from 95.0±0. 1 in normoxia. V0₂ during exercise was not different among the three conditions. Exercise-induced La accumulation was increased by hypoxia. E and NE during exercise were not affected by hypoxia statistically. There was a significant correlation between La and E (P<0.01) and between La and NE (P<0.01) during exercise in the three conditions. The present findings suggest a relationship between glycogen metabolism and sympathoadrenal activity which results in an increase of plasma catecholamines during exercise in humans acutely exposed to hypoxia.