Plasma free, erythrocyte free and plasma peptide amino acid exchange to calves in steady state and fasting metabolism.

Arteriovenous differences in plasma free, erythrocyte free and plasma peptide amino acids were measured across the hindlimbs of growing Holstein steer calves (147 kg) surgically fitted with abdominal aorta and caudal vena cava cannulae. Animals were maintained in a near "steady state" metabolism by feeding at hourly intervals in a continuously lighted environment. The "steady state" blood samples were obtained 10 days post-surgery; then the animals were fasted for 72 hours and resampled. In the fed animal most amino acids were removed from the plasma free and plasma hindlimbs. Glutamine was the only amino acid released by the hindlimbs into the plasma free pool of fed animals. The branched-chain and acidic amino acids were removed by the hindlimbs from the plasma peptide pool while the basic amino acids exhibited nominal involvement. Alanine and lysine were removed while glycine, aspartate and glutamate were added to the erythrocyte as the tissue was traversed. Fasting resulted in a release from the hindlimbs of most amino acids into all pools monitored. Serum total proteins and glutathione were removed from blood in fed animals and added to the blood of fasted animals. Several pools transport amino acids to tissues and the relative importance of a particular pool varies with amino acid and nutritional status.