DESIGN OF THE OXYGEN AND SUBSTRATE PATHWAYS .3. PARTITIONING ENERGY PROVISION FROM CARBOHYDRATES

This paper quantifies maximal fluxes through the pathway supplying car bohydrates to the mitochondria of muscle cells, Continuous infusions o f D-[3-H-3]glucose together with indirect calorimetry were used to inv estigate the partitioning of the supply of carbohydrates through the t wo branches of the pathway: from circulating glucose and from glycogen stores within the muscle cells to the mitochondria, The relative cont ribution of circulating glucose to total carbohydrate oxidation was sm all, accounting for only 13 % and 23 % of the carbohydrate oxidized at exercise intensities approaching M(O2max) in dogs and goats, respecti vely, Unexpectedly, maximal rates of circulating glucose oxidation wer e nearly the same in the two species (when expressed in absolute terms ; dog:goat ratio = 1.2), despite the 2.2-fold difference in aerobic ca pacity, We conclude that the glycogen stores in the muscle cells are t he major source of substrates at maximal rates of oxidation, supplying 60-70 % of the total energy, Furthermore, it is this branch of the ca rbohydrate pathway that is adapted to the large difference in aerobic capacity between dogs and goats.