MISMATCH BETWEEN LIPID MOBILIZATION AND OXIDATION - GLYCEROL KINETICSIN RUNNING AFRICAN GOATS

Glycerol kinetics and total fatty acid (FA) oxidation of trained Afric an pygmy goats were measured by continuous infusion of [2-H-3]glycerol and indirect calorimetry during treadmill exercise at 40, 60, and 85% maximal O2 consumption (VO2 max). Our main goals were 1) to determine whether rates of FA mobilization and utilization are eventually match ed as exercise intensity increases, thereby minimizing reesterificatio n to supply more FA to working muscles, and 2) to test the hypothesis that lipolytic rate is proportional to aerobic capacity by comparing l ow-aerobic goats with published values from highly aerobic dogs and hu mans. Mean rate of glycerol release in the circulation (R(a) glycerol) was 3.83 +/- 0.11 at rest, 7.69 +/- 0.88 at 40% VO2 max reached a max imum of 15.32 +/- 0.95 at 60% VO2 max, and returned to 10.53 +/- 0.76 mumol.kg-1.min-1 at 85% VO2 max. Lipolytic rate did not match total FA oxidation, implying that R(a) glycerol cannot be used as an index of FA utilization, even during intense exercise. A large fraction of tota l FA released by lipolysis was reesterified at 60 and 85% VO2 max, sho wing that FA mobilization does not limit whole animal FA oxidation at these intensities. Comparing goat, dog, and human responses reveals th at mammalian lipolytic rate is scaled with aerobic capacity. High- and low-aerobic species exercising at the same %VO2 max mobilize FA in ex act proportion with their metabolic rate, suggesting that the relative contribution of FA to total energy provision is independent of VO2 ma x.