Amino acid uptake and output by the sheep hind limb.

Arteriovenous differences across the hind limb of fed sheep show release of alanine, glutamine, and tyrosine and uptake of serine, glutamate, and possibly lysine. In starved animals there is a net output of most amino acids, although the amount of alanine released, 26 nmol/ml blood, is much lower than reported for human muscle and is less than the cumulative release of valine, leucine, and isoleucine. Since it has been argued that the carbon of alanine is derived from glucose and the nitrogen from the deamination of branched chain amino acids, we suggest that either nutrient availability is limiting alanine output or else sheep muscle has an impaired ability to degrade the branched chain amino acids.