The effect of fructose infusions on the oxygen transport system of human blood

In 9 healthy subjects the erythrocyte 2,3-diphosphoglycerate (2,3-DPG) concentration, which modifies the oxygen affinity of haemoglobin, decreased by more than 25 per cent within 60 minutes of the beginning of a fructose infusion (0.5 g.kg body weight-1.h-1). In contrast erythrocyte adenosine triphosphate (ATP) concentration was unchanged. In spite of the diminished 2,3-DPG concentrations the oxygen affinity of whole blood actually measured remained unaltered. However, at the same time both the arterial and the venous blood pH had fallen by 0.05 or more. In vitro experiments indicated that this fall of erythrocyte 2,3-DPG was not due to a direct effect of fructose on the intra-erythrocytic regulation of 2,3-DPG or to changes indirectly related to the intravenous administration of fructose in vivo, i.e. an increase of the blood lactate/pyruvate ratio or a decrease of plasma inorganic phosphate. It is suggested that two opposing effects on the oxygen transport system of blood are induced by fructose infusions: 1) a displacement of the oxygen dissociation curve to the right due to the Bohr effect 2) a virtually counterbalancing shift of the oxygen dissociation curve to the left due to decreased erythrocyte 2,3-DPG concentrations.