Muscle metabolism during rest and exercise: influence on the oxygen transport system of blood in normal and diabetic subjects.

The oxygen dissociation curve shifted less to the right in venous blood draining from muscle in eight insulin-deficient diabetics working at a constant submaximal workload than in seven normal controls (28.7 mm. Hg vs. 30.8 mm Hg; P less than 0.05). This diminution of the in-vivo Bohr effect at the muscle tissue level during exercise in diabetics was due to a significantly smaller decrease of venous blood pH (down to 7.33 vs. 7.27 in normals; P less than 0.05), probably a consequence of an latered muscle metabolism in insulin deficiency. Although no glucose was taken up, even during exercise, and less lactate was produced by insulin-deficient muscle (P less than 0.05), the differences in venous blood pH appeared to be brought about mainly by a different CO2 production of the exercising muscle in the two groups. The response of Krebs cycle activity to exercise in insulin-deficient muscle might have been inadequate, as suggested by the increased 3-hydroxybutyrate/acetoacetate ratio in the venous blood observed in the normal controls but not in the diabetics. Furthermore, proportionally less of the arterial ketone body concentration was utilized by the working muscle in the insulin-deficient diabetics. Changes in erythrocyte 2,3-diphosphoglycerate did not contribute to the differences in the in-vivo Bohr effect.