Abstract des Autors

The extent to which carbohydrate (CHO) availability affects free fatty acid (FFA) metabolism in contracting skeletal muscle is not well characterized. To study this question, rats were depleted of glycogen by swimming exercise and lard feeding 24 h before perfusion of their isolated hindquarters. After 20 min of preperfusion with a medium containing no glucose, palmitate (600 or 2,000 micro-M), and [1-14C]palmitate, flow was restricted to one hindlimb, which was electrically stimulated for 2 min to further deplete muscles of glycogen. After 2 min of recovery, glucose was added to the perfusate at final concentrations of 0, 6, or 20 mM, and after another 3 min muscles were stimulated for 30 min. At 6 and 2,000 micro-M palmitate, glucose uptake after 30 min of stimulation averaged 23.5+/-9.3 and 45.9+/-10.6 micro-mol/g/h with 6 and 20 mM glucose, respectively. At 6 and 2,000 micro-M palmitate, palmitate uptake was lower with 0 than with 6 or 20 mM glucose. At 600 micro-M palmitate, percent palmitate oxidation was higher with 0 than with 6 or 20 mM glucose, resulting in similar total palmitate oxidation with the three glucose concentrations. At 2,000 micro-M palmitate, percent palmitate oxidation was not significantly different among glucose concentrations, resulting in a significantly lower rate of palmitate oxidation with 0 than with 6 or 20 mM glucose. Muscle levels of malate and citrate and ammonia release from contracting muscle were not significantly different among glucose concentrations. It is concluded that, at a constant FFA concentration, contracting skeletal muscle does not compensate for low CHO availability by increasing uptake and oxidation of FFA. At high FFA concentration, low CHO availability is accompanied by a decrease in FFA oxidation that is not associated with a decrease in the level of tricarboxylic acid cycle intermediates. Verf.-Referat