EFFECT OF ACUTE PLASMA-VOLUME EXPANSION ON SUBSTRATE TURNOVER DURING PROLONGED LOW-INTENSITY EXERCISE

We investigated the effect of acute, graded increases in plasma volume (PV) by use of dextran on substrate turnover and oxidation during exe rcise. Eight untrained males [peak aerobic power ((V) over dotO(2peak) ) = 45.2 +/- 2.2 (SE) ml.kg(-1).min(-1)] performed 2 h of cycle ergome try at 46 +/- 4% of (V) over dotO(2peak) on three occasions in a rando mized order: 0% PV expansion (CON) and after 14% (LOW) and 21% (HIGH) PV expansion. Glucose and glycerol turnover were measured using primed continuous infusions of [6,6-H-2(2)]glucose and [H-2(5)]glycerol, res pectively. Glycerol rate of appearance (R-a) was taken as a relative i ndex of whale body lipolysis. Increases in PV had no effect on glucose R-a or disappearance (R-d) either at rest or during exercise. At the onset of exercise, both glucose R-a and R-d increased similar to 100% (P < 0.01). Glucose R-a and R-d continued to increase with exercise du ration (P < 0.05) so that, at 120 min of exercise, they were >330% hig her than at rest (P < 0.01). Glycerol R-a also increased with exercise duration (P < 0.05). Total lipolysis during exercise, calculated as t he area under the glycerol R-a vs. time curve, was reduced during LOW vs. CON (P < 0.01). Further expansion of PV (HIGH) had no additional e ffect on whole body lipolysis. No effect of hypervolemia was observed on whole body fat or carbohydrate oxidation. These results indicate th at acute PV expansion can alter whole body lipolysis, possibly via a r eduction in catecholamine secretion.