Effects of carbohydrate and protein administration on rat tryptophan and 5-hydroxytryptamine: differential effects on the brain, intestine, pineal, and pancreas

We compared the acute effects of intragastric administration of protein and carbohydrate on tryptophan and 5-hydroxytryptamine (5HT) in rat brain, pineal, intestine, and pancreas. Protein decreased and carbohydrate increased brain indoles relative to water-infused controls. These effects were due to competition between the large neutral amino acids for entry into the brain. This competition does not exist in the pineal. The macronutrients had no effect on pineal tryptophan metabolism. In the intestine, protein resulted in higher tryptophan levels as compared to controls, owing to absorption of tryptophan in the protein. However intestinal 5HT levels were influenced by factors other than precursor availability. Pancreatic indoles were affected in a similar manner to the brain indoles. Competition between the large neutral amino acids for entry into the pancreas was also indicated by the finding that valine administration lowered brain and pancreatic tryptophan, but not the levels in the intestine and pineal. It remains to be seen whether the decrease in pancreatic 5HT after a protein meal and the increase after carbohydrate modulate the release of insulin and glucagon.

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Acute effects of aspartame on large neutral amino acids and monoamines in rat brain

Life Sciences ◽

10.1016/0024-3205(83)90873-1 ◽

1983 ◽

Vol 32 (14) ◽

pp. 1651-1658 ◽

Cited By ~ 48

Author(s):

John D. Fernstrom ◽

Madelyn H. Fernstrom ◽

Marcia A. Gillis

Keyword(s):

Amino Acids ◽

Rat Brain ◽

Acute Effects ◽

Large Neutral Amino Acids ◽

Neutral Amino Acids

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Atypical amino acids inhibit histidine, valine, or lysine transport into rat brain

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1983.245.4.r556 ◽

1983 ◽

Vol 245 (4) ◽

pp. R556-R563 ◽

Cited By ~ 1

Author(s):

J. K. Tews ◽

A. E. Harper

Keyword(s):

Amino Acids ◽

Rat Brain ◽

Blood Brain Barrier ◽

Brain Slices ◽

Aromatic Amino Acids ◽

Brain Barrier ◽

Basic Amino Acids ◽

Large Neutral Amino Acids ◽

Neutral Amino Acids ◽

Single Meal

Transport of histidine, valine, or lysine into rat brain slices and across the blood-brain barrier (BBB) was determined in the presence of atypical nonprotein amino acids. Competitors of histidine and valine transport in slices were large neutral amino acids including norleucine, norvaline, alpha-aminooctanoate, beta-methylphenylalanine, and alpha-aminophenylacetate. Less effective were aromatic amino acids with ring substituents; ineffective were basic amino acids and omega-amino isomers of norleucine and aminooctanoate. Lysine transport was moderately depressed by homoarginine or ornithine plus arginine; large neutral amino acids were also similarly inhibitory. Histidine or valine transport across the BBB was also strongly inhibited by large neutral amino acids that were the most effective competitors in the slices (norvaline, norleucine, alpha-aminooctanoate, and alpha-aminophenylacetate); homoarginine and 8-aminooctanoate were ineffective. Homoarginine, ornithine, and arginine almost completely blocked lysine transport, but the large neutral amino acids were barely inhibitory. When rats were fed a single meal containing individual atypical large neutral amino acids or homoarginine, brain pools of certain large neutral amino acids or of arginine and lysine, respectively, were depleted.

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Stimulated amino acid imbalance and histidine transport in rat brain slices

American Journal of Physiology-Legacy Content ◽

10.1152/ajplegacy.1975.229.1.229 ◽

1975 ◽

Vol 229 (1) ◽

pp. 229-234 ◽

Cited By ~ 12

Author(s):

J Lutz ◽

JK Tews ◽

AE Harper

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Brain Slices ◽

Amino Acid Mixture ◽

Acid Mixture ◽

Large Neutral Amino Acids ◽

Neutral Amino Acids ◽

Low Protein ◽

Amino Acid Imbalance ◽

The Brain

Histidine concentration in the brain decreases rapidly when rats are fed a low protein diet in which an amino acid imbalance is created by addition of an amino acid mixture devoid of histidine. Competition for histidine transport into the brain was suggested as an explanation for this effect. Therefore, animo acid mixtures simulating composition of plasma from rats fed basal or histidine-imbalanced diets were added to media to evaluate their effects on uptake of histidine by brain slices during a 60-min incubation period. At the concentrations actually found in plasma, the unbalanced mixture decreased histidine uptake significantly more than did the basal mixture. Two distinct inhibition patterns were observed with different groups of amino acids: a linear decrease in histidine uptake with a mixture of the small neutral, hydroxyl, basic, and acidic amino acids, and a hyperbolic decrease with a mixture of large neutral amino acids, and a hyperbolic decrease with a mixture of large neutral amino acids. Inhibition of histidine transport by the complete mixtures reflected these two effects. Plasma patterns and concentrations of competitive amino acids as well as the concentration of histidine appear to be factors involved in decreasing histidine transport into the brain.

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