Diurnal changes of the 2,3-diphosphoglycerate concentration in human red cells and the influence of posture.

The 2,3-diphosphoglycerate (2,3-DPG) concentration, oxygen half saturation pressure at pH 7.4 (P50), pH in plasma and red cells, and mean corpuscular hemoglobin concentration (MCHC) of venous blood were determined during unrestricted daily activity (series I) throughout 24 hrs as well as during prolonged bed rest until noon (series II). In series I almost synchronous dirunal behavior of P50 2,3-DPG, and plasma pH as well as red cell pH became significantly apparent with highest values in the afternoon.