EXERCISE-INDUCED CHANGES IN PLASMA VITAMIN-B-6 CONCENTRATIONS DO NOT VARY WITH EXERCISE INTENSITY

This study examined the effect of high vs moderate exercise intensity on changes in concentration of plasma pyridoxal 5'-phosphate (PLP), py ridoxal (PL), and 4-pyridoxic acid (4-PA) in human subjects. Eight phy sically active subjects were tested twice at 60% and 85% maximum oxyge n consumption (VO(2)max) for 30 and 20 min, respectively, on a bicycle ergometer. Blood samples were obtained before and during exercise. Da ta were adjusted for changes in plasma volume calculated from changes in hematocrit. PLP concentration significantly increased during exerci se (P < 0.0001), with 79% of the rise in PLP concentration occurring w ithin 5 min. 4-PA concentration increased steadily through exercise an d was 23% higher at 20 min than at 0 min. Exercise intensity had no ef fect on the magnitude or rate of either increase for either PLP or 4-P A. PL concentration did not vary with exercise duration, but was signi ficantly higher at 60% compared with 85% VO(2)max (P = 0.001). No sign ificant differences were observed in glucose concentration. The data d o not support hypotheses in the literature that PLP concentration rise s during exercise to support exercise-induced shifts in substrate util ization.