Determination of glutamate requirement in growing rats by indicator amino acid oxidation

Abstract

Although many studies have investigated requirements for essential amino acids both in animals and human, few have done for non‐essential amino acids (NEAAs). This study aimed to determine requirement for glutamate (Glu), the most abundant NEAA in food proteins, in growing rats by the indicator amino acid oxidation (IAAO) method.Wistar strain male rats (6wks old) were given fixed amount of diets containing varied doses of amino acid (AA) mixture with NRC 1995 composition (56–214 g/kg) hourly. Dietary labeling with an indicator AA ([1‐13C]leucine) started at 3h of feeding period and 13C‐enrichments of breath CO2 were monitored. Relation between dietary AA contents and IAAO (= average 13C‐enrichments from 4 to 7h) was analyzed to determine a breakpoint as its requirement. Similarly, relation between dietary Glu content and IAAO was analyzed in rats fed diets containing graded doses of Glu (0–100 g/kg).In both experiments, increase of AA or Glu contents at lower doses reduced IAAO, but did not further at higher doses. Apparent breakpoints were determined in their biphasic relations, indicating 173 and 45 g/kg diet of requirements for AA and Glu, respectively. Glu requirement estimated in this study was almost identical with the value determined by nitrogen‐balance study. These results indicated the existence of Glu requirement and suggested importance of dietary Glu as one of components of protein nutrition.