Uptake and release of free fatty acids and other metabolites in the legs of exercising men.

Abstract

The contribution of metabolites in blood plasma to oxidative metabolism in leg tissues during exercise on a bicycle ergometer was estimated from analyses of arterial and femoral venous blood in subjects receiving a constant intravenous infusion of palmitate-I-14C. Extraction fraction of free fatty acids (FFA) in leg tissues was lower during exercise than at rest, but influx of FFA into the legs was greater. During exercise, output of 14C in blood CO2 approximately equaled input from plasma FFA within 1 hr. Plasma FFA supplied approximately half and plasma triglyceride fatty acids less than 10% of the fatty acids burned in the leg during exercise, estimated from gas exchanges. Release of glycerol was insignificant. Uptake of glucose-carbon from the blood averaged 16% of CO2 output and an amount of lactate equivalent to one-third of glucose-carbon was released from the legs. It is suggested that about half of the fatty acids and more than half of the glucose oxidized in the leg were derived from local stores of lipid and carbohydrate.