Acceptability by rats of aqueous solutions of amino acid analogues.

Preferences differed widely when rats were offered choices between water and solutions of various natural amino acids and structurally related analogues. They avoided the branched-chain amino acid valine but preferred solutions of its isomer norvaline and of norleucine. The hydrochloride forms of ornithine and arginine were preferred to water at concentrations up to about 100 mM and avoided at 410 mM; homoarginine.HCl was never preferred and was avoided at 39 and 78 mM. Rats were indifferent to taurine and beta-alanine at most concentrations but refused these amino acids at high concentrations (205 and 410 mM, respectively). In conjunction with earlier observations on feeding behavior in response to dietary additions of amino acids, the results show that selections by rats between water and amino acid solutions cannot be used to predict choices among amino acid-containing diets.