Effects of phosphate loading on 2,3-diphosphoglycerate and maximal oxygen uptake

Increased concentration of red blood cell 2,3-diphosphoglycerate (RBC 2,3-DPG) shifts the hemoglobin-oxygen dissociation curve to the right, thus theoretically allowing better oxygenation of tissues. To determine whether such a shift is physiologically significant, we investigated the effects of oral phosphate loading on several parameters including plasma phosphate concentration, RBC 2,3-DPG, hematocrit and hemoglobin concentration, maximal oxygen uptake (VO2max), and degree of lactic acidemia in 10 well-trained distance runners. After control determinations were made, either a phosphate load or a placebo was given for 3 d before the athlete was restudied. A placebo and two phosphate-loading studies were performed at weekly intervals, followed by 2 wk of rest and another post-intervention control study. Blood samples for control values were drawn before and after a standard warm-up period, after treadmill exercise at a 10% grade, and at the completion of the VO2 determination. After oral phosphate loading there was a significant increase in serum phosphate and RBC 2,3-DPG. Maximal oxygen uptake was significantly increased and correlated with the rise in RBC 2,3-DPG (r = 0.81). The increase in blood lactate after exercise on the 10% grade was attenuated during sessions which followed phosphate loading.