EFFECT OF HIGH FFA ON GLYCOGENOLYSIS IN OXIDATIVE RAT HINDLIMB MUSCLES DURING TWITCH STIMULATION

The effect of elevated free fatty acids (FFA) on carbohydrate (CHO) ut ilization in the oxidative muscles of the isolated rat hindlimb was de termined using twitch contraction paradigms evoking a wide range of O- 2 uptakes and glycogenolysis. The hindlimb was perfused with either 0 or 1.8 mM FFA for 10 min at rest and then subjected to 20 min of stimu lation at 0.4, 0.7, 1, 2, 3, or 4 Hz. Soleus (Sol), plantaris (Pl), an d red gastrocnemius (RG) were sampled after rest perfusion or stimulat ion. FFA had little effect on glycogenolysis during stimulation, altho ugh glycogen sparing occurred with one of the lesser intensity protoco ls in each muscle (Sol, 0.4 Hz; RG, 0.7 Hz; Pl, 1 Hz). Muscle citrate and acetyl-CoA were elevated in Sol during several stimulation protoco ls with high FFA, but this effect was inconsistent in Pl and RG. The s paring of glycogen, when it did occur, was generally unrelated to incr eases in either citrate or acetyl-CoA content. Furthermore, protocols in which citrate or acetyl-CoA were elevated in the presence of elevat ed FFA did not demonstrate glycogen sparing. Hindlimb lactate efflux a t rest was reduced with FFA but unaffected during stimulation. Glucose uptake was unaffected by FFA at rest and during all stimulation proto cols, except 3 Hz. The present study does not support the classically proposed roles of citrate and acetyl-CoA in the FFA-induced downregula tion of CHO utilization in electrically stimulated rat skeletal muscle .