Human forearm arteriovenous differences of carnitine, short-chain acylcarnitine and long-chain acylcarnitine.

1. Forearm arterial and venous concentrations of free carnitine, short-chain acylcarnitine, long-chain acylcarnitine, glucose, lactate, pyruvate, alanine, non-esterified fatty acids, glycerol, 3-hydroxybutyrate and acetoacetate were measured in fasted adult subjects. 2. In all subjects there was net uptake of short-chain acylcarnitine, 3-hydroxybutyrate and acetoacetate and net release of free carnitine and non-esterified fatty acids. The arteriovenous differences of the other metabolites were not consistent. 3. These observations support the concept that short-chain acylcarnitine (largely acetylcarnitine) contributes to the flux of metabolic fuels from the liver to muscle in the fasted state, although to a limited extent in comparison with 3-hydroxybutyrate (less than 5% on a molar basis).