Plasma amino acid curve in rats force-fed a single meal lacking an essential amino acid

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Abstract
The amino acid levels in plasma and liver were determined in rats at various time intervals after giving the animals a single meal of a complete amino acid diet (CAA) or a diet devoid of either leucine, isoleucine, or threonine. Male rats were fed by stomach tube and they were killed at 0, 2, 4, 6, or 8 hours postprandial. Amino acid analyses were performed on deproteinized supernatants of plasma and liver. The changes in the plasma amino acid levels occurred within 2 hr after feeding a single meal of either the diet lacking leucine or CAA. The values of most of the amino acids attained their highest levels at 4 hr postprandial and many amino acids were declining in concentration at 6 and 8 hr. Isoleucine and valine showed very high levels in plasma at 2, 4, 6 and 8 hr after feeding the diet devoid of leucine. The amino acid levels in liver reflected the amino acid concentrations in plasma at each time interval. Rats fed the diets devoid of either isoleucine or threonine demonstrated less alterations in plasma amino acid concentrations with only a few amino acids changed. After giving a single meal the amino acid levels in plasma are transient since many of the amino acids show similar values at the 0- and 8-hr intervals. The alterations in amino acid levels in plasma that occur after feeding are dependent upon both the identity of the essential amino acid omitted from the diet and the postprandial time.