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Abstract
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.