Effect of amino acid supplementation to low protein diet on brain and plasma levels of tryptophan and brain 5-hydroxyindoles in rats.
The contribution of amino acid transport across the blood-brain barrier toward the concentration of brain 5-hydroxyindoles [serotonin and 5-hydroxyindole acetic acid (5HIAA)] was investigated. Several amino acids were individually supplemented to a 5% whole egg protein diet. Close correlation between serum tryptophan, brain tryptophan and 5-hydroxyindoles were observed regardless of diet fed. When a large neutral amino acid (LNAA such as methionine, threonine, leucine or phenylalanine) was added to the control diet, brain 5-hydroxyindole concentration was lower than when the control diet was fed; however, when tryptophan was added, brain 5-hydroxyindole concentration was significantly higher. Lysine supplementation did not affect brain 5-hydroxyindole concentration. Leucine supplementation caused a lower tyrosine concentration in hypothalamus than the control diet, but phenylalanine supplementation caused higher hypothalamus level of tyrosine. There was no correlation between tyrosine and norepinephrine concentrations in hypothalamus (norepinephrine turnover might also be changed by the nutritional state). These observations indicate that the supplementation of an amino acid at two- or fourfold of the requirement to a low protein diet can generate major changes in the concentrations of neurotransmitters in rats.
D000596:Amino Acids / Q000494:pharmacology*; D000818:Animals; D001921:Brain / Q000378:metabolism*; D004044:Dietary Proteins / Q000494:pharmacology*; D005260:Female; D007031:Hypothalamus / Q000378:metabolism; D007211:Indoles / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D014364:Tryptophan / Q000097:blood / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism
D000596:Amino Acids; D004044:Dietary Proteins; D007211:Indoles; C026785:5-hydroxyindole; D014443:Tyrosine; D014364:Tryptophan; D009638:Norepinephrine