Uptake of chylomicron triglycerides by contracting skeletal muscle in rats

The influence of muscle stimulation (3 Hz) on the uptake of exogenously administered chylomicron 14C-labeled triglycerides (14C-TG) in the three different muscle fiber types was evaluated in fed and fasted pentobarbital-anesthetized rats. The fractional uptake of 14C-TG in the nonstimulated muscles was lowest in the fast-twitch white, intermediate in the fast-twitch red, and highest in the slow-twitch red muscle fiber section. Fasting doubled the uptake in both high-oxidative red fibers. These 14C-TG uptakes were directly proportional (r = 0.993) to their respective activities of lipoprotein lipase in these fiber types of fed and fasted animals reported by others. Muscle stimulation caused a significant increase in the fractional 14C-TG uptake in all of the fiber types. Although the TG uptake could account for only a small fraction of the total energy needs of the working muscle, it could contribute to the turnover of endogenous TG, especially in the slow-twitch red fibers. Further, the estimated TG uptake rate is sufficient to replace endogenous TG loss with an overnight rest following exercise. These results suggest that plasma TG could play an important role in lipid metabolism, especially in the high-oxidative slow and fast muscle fiber types.