Taste preference and protein nutrition and L-amino acid homeostasis in male Sprague-Dawley rats.

Changes in taste preference were investigated in a choice paradigm using rats under various states of protein nutrition. A preference for the umami taste substances, monosodium L-glutamate (MSG) with or without 5'-ribonucleotide (5'-guanosine monophosphate), was induced when dietary protein was within the normal range, but a preference for NaCl occurred under its marginal deficiency. A preference for both NaCl and glycine was induced under severe protein malnutrition, possibly reflecting the body's negative nitrogen balance. The strength of this preference paralleled the body's requirement for protein, and thus, like the protein requirement for normal growth, declined with age. When animals with L-lysine (Lys) deficiency consumed a Lys solution and began to grow normally, their intake of taste stimulus solutions changed from preferring NaCl and glycine to preferring MSG. The regulatory mechanism of preference for L-amino acid (AA) in rats deficient of an essential AA was related to the pattern of AA in plasma and brain. Data suggest that umami taste perception plays an important role in protein metabolism, and in maintenance of AA and ammonia homeostasis within normal limits.