ENHANCED CARDIAC METABOLISM OF PLASMA-GLUCOSE IN HIGH-ALTITUDE NATIVES - ADAPTATION AGAINST CHRONIC HYPOXIA

The metabolism of glucose in mammalian heart is 25-50% more O-2 effici ent than the metabolism of free fatty acids. To assess the role of sub strate preference in adaptations to chronic hypoxia, positron emission tomographic measurements of heart regional glucose uptake rates after an overnight fast were made in volunteer Quechua subjects and in Sher pa subjects, both indigenous to altitudes of over 3,000 m, and in a gr oup of lowlander volunteers. Highest uptake rates were found in the an d Quechuas on arrival and in the Sherpas after a 3-wk period at low al titude, intermediate rates in Quechuas after a 3-wk period at low alti tude and in the lowlanders, and lowest rates in Sherpas on arrival. Th ese low values were probably related to the stress of travel to the si te of the experiments. Measured plasma catecholamines, hormones, and s ubstrates indicated that glucose concentrations correlated best with o bserved variations in glucose uptake, with a negative correlation for the control subjects and a positive correlation for the Quechuas and S herpas. Uptake values in Quechuas declined significantly after a 3-wk period at low altitude, but the positive correlation with glucose leve ls persisted. We conclude that an elevated glucose preference in heart is a true metabolic adaptation in humans adapted over generations to chronic hypoxia.