CIRCULATING PALMITATE UPTAKE AND OXIDATION ARE NOT ALTERED BY GLYCOGEN DEPLETION IN CONTRACTING SKELETAL-MUSCLE

The extent to which muscle glycogen depletion affects plasma free fatt y acid (FFA) metabolism in contracting skeletal muscle is not well cha racterized. To study this question, rats were glycogen depleted (GD) o r supercompensated (SC) by swimming exercise and diet treatment 24 h b efore perfusion of their isolated hindquarters at rest and during elec trically induced muscle contractions. After 20 min of equilibration wi th glucose (6 mM), palmitate (2,000 mu M), and [1-C-14]palmitate, palm itate uptake and oxidation were found to be similar between groups at rest and during electrical stimulation. Palmitate uptake increased by 55% during electrical stimulation and averaged 2.75 +/- 0.56 mu mol . g(-1). h(-1). Resting palmitate oxidation averaged 0.14 +/- 0.03 mu mo l . g(-1). h(-1) and increased to 0.53 +/- 0.06 and 0.47 +/- 0.08 mu m ol . g(-1). h(-1) during electrical stimulation in GD and SC, respecti vely. Glucose uptake was significantly higher in GD than in SC at rest and during electrical stimulation and significantly increased in both groups during electrical stimulation to reach values of 11.8 +/- 1.2 and 7.6 +/- 1.4 mu mol . g(-1). h(-1), respectively. Lactate release w as lower in GD than in SC at rest and during electrical stimulation an d was highest after 2 min of stimulation in both groups. Additional ex periments at perfusate palmitate concentrations of 600-900 mu M yielde d similar results. These results show that, in contracting perfused sk eletal muscle, muscle glycogen depletion increases glucose utilization but does not affect total plasma FFA oxidation, suggesting that regul ation within pathways of carbohydrate metabolism takes precedence over regulation between pathways of lipid and carbohydrate metabolism.