Metabolism of free fatty acids and chylomicron triglycerides during exercise in rats

Abstract

Unanesthetized fasted rats were injected intravenously with palmitate 1-14c-or glycerol-3H, palmitate-1-14c-labeled-chylomicrons while they were running in an exercise cage. Distribution of radioactivity in lipids of tissues, corrected for that remaining in trapped plasma, was compared with that obtained in resting rats. Exercise decreased the amount of 14C in tissue lipids of animals killed 2 min. after injection of labeled palmitate. 14C in liver was reduced to one-third that observed at rest, whereas that in cardiac and skeletal muscle was altered little. Exercise increased the rate chylomicron-radioactivity was removed from the blood of rats killed 3-4 min after injection. Uptake in liver was unchanged, but the fraction taken up in cardiac and skeletal muscle plus that oxidized was greater in exercised animals. Hydrolysis of chylomicron triglycerides in all rats, estimated from the ratio of 3H to 14C in tissue lipids, was extensive in muscle and adipose tissue, moderate in spleen, and slight in liver, and oxidation of 14C was similar to that observed after injection of palmitate-14C.