An asparagine requirement in young rats fed the dietary combinations of aspartic acid, glutamine, and glutamic acid

Abstract

The effect of dietary asparagine on rat growth was investigated. Diets were formulated with L amino acids so as to contain asparagine, aspartic acid, glutamine and/or glutamic acid in all possible combinations and then fed to weanling rats for 3 weeks. Of the 4, only asparagine was found to be essential for optimal growth, and it was essential regardless of the presence or absence of any dietary combination of these related amino acids. In selected dietary groups, the unbound asparagine levels were measured in various tissues over an 8 day period. Muscle asparagine levels were reduced for asparagine deprived animals over the entire period studied; brain levels were decreased only after 7 days of dietary depletion, while hepatic levels were unaffected by dietary asparagine deprivation. In a related series, animals were more drastically depleted of asparagine by combining dietary deprivation with asparaginase treatment, causing a rapid decrease in cellular concentration of asparagine, which affected protein and DNA synthesis for those organs undergoing hyperplastic growth. Thus, asparagine may be rate limiting to protein synthesis for this extreme case as well as during dietary asparagine deprivation, which also decreased intracellular levels of unbound asparagine and led to irreversible deficits in development.