Self-selection of amino acid and protein, and brain serotonin concentration in rats.

Abstract

Theeffects of intraperitoneally injecting pargyline, which elevates the brain serotonin (5-HT) content, and p-chlorophenylalanine (j?-Cl-Phe), which lowers the brain 5-HT content, on food selection in growing rats choosing freely between two diets containing various amounts of amino acid (Val, Thr or Trp) or protein (casein) were investigated.Under the conditions of this experiment, no consistent correlation was observed between the amount of amino acid or protein intake and the plasma ratio of Trp to large neutral amino acids (Trp/LNAA). Also, neither the amino acid nor protein intake under the conditions of the selection paradigm wasaffected, despite the brain neurotransmitter (5-HT) concentration being markedly altered. These results suggest that the concentration of 5-HTin the whole brain will not regulate the amino acid or protein intake and selection. The behavioral aspect of selection for dietary amino acid or protein appears to be related to the maintenance of amino acid concentrations in the blood and brain within normal limits, regardless of the brain 5-HT level.Studies done in our laboratory1~7) have demonstrated that, in growing rats allowed to choose between two diets varying only in individual essential amino acid content, the intake of these amino acids was regulated at levels sufficient to meet the animals' requirements. The mechanism responsible for amino acid intake is not yet clearly understood.

Self-selection of Dietary Branched-chain Amino Acids by Rats

“…Amino acid concentrations in plasma and brain were measured by the same method as in our previous report. 7 ) …”