The mechanism underlying increased plasma albumin content associated with exercise-induced hypervolemia
We measured changes in plasma volume (PV) and albumin (Alb) content in 7 subjects for 22 h following 72 min of intermittent upright (U) and supine (S) exercise at 85% of peak oxygen uptake. To evaluate Alb synthesis, we continuously infused 2Hs ring-phenylalanine (ds-Phe) and calculated fractional synthetic rate (FSR) from the abundance of ds-Phe in plasma free and albumin-bound Phe, measured by gas chromatographymass spectrometry. By 22 h following exercise, the increase in PV from control was greater (P<0.05) in U than in S (U, 2.69 0.76; S, -1.74 0.97 ml/kg bw). Alb content in U was elevated (P<0.05) from control by 0.13 0.03 g/kg bw at 1 h following exercise and remained at that level until the end of experiment. Alb content in S did not change throughout the experiment (-0.02 0.03 g/kg bw at 22 h following exercise). FSR changed from 3.52 0.55 and 3.27 0.39%/day before exercise to 6.00 1.03 and 1.15 0.90%/day by 22 h following exercise in U and S, respectively. We surmise that the increase in Alb content in U is partly attributable to the increased Alb synthesis; however, redistribution of interstitial Alb into the intravascular space is responsible for the immediate increase in Alb after exercise. Further, factors associated with posture are important as the stimulus for the increase in plasma Alb after exercise.