Induction of lysine imbalance in rats: relationships between tissue amino acids and diet.

We examined the ability of wheat gluten or casein diets supplemented with arginine, indispensable (IAA) or branched-chain (BCAA) amino acids (inhibitors of lysine transport into brain slices in vitro) to induce changes in tissue lysine concentrations consistent with occurrence of lysine imbalance. Tissue lysine concentrations were several-fold higher in male, 60--65 g rats of the Sprague-Dawley strain fed for 1 day a 6% casein basal diet than in rats fed wheat gluten basal diets. Feeding a casein diet containing 5% of a mixture of all IAA except lysine changed concentrations of lysine and other amino acids to resemble those from rats fed wheat gluten diets. Growth depressions caused by arginine were consistently associated with large decreases in brain lysine concentrations and large increases in tissue arginine and ornithine concentrations. Growth depressions caused by supplements of BCAA or IAA were frequently accompanied by small or insignificant decreases in brain lysine content, and by small increases in tissue content of these amino acids. Plasma lysine concentrations were generally decreased less than were those in brain. The arginine-induced decrease in brain lysine concentration is consistent with the hypothesis that induction of amino acid imbalances may involve competition for transport into the brain of an indispensable, limiting amino acid; growth depressions caused by BCAA or IAA appear to involve other factors as well.