Uniqueness of Tryptophan in the Transport System in the Brain and Peripheral Tissues

Amino acids are important substances that must be transported to tissues such as the brain and muscles. The process is considered insulin dependent. It is not known whether all the amino acids are almost equally dependent in their transportation to tissues. We want to know whether some important amino acids are transported differently from other amino acids. Especially tryptophan is important because it is converted to serotonin, melatonin or kynurenine. Results showed that Amino acids levels in the plasma were measured after the intakes of 50 grams of glucose or sucrose to young (18 - 22 years old) and old (≥50 years old) men. Total amino acids in the plasma decreased after the intakes of glucose. Total amino acids levels decreased more significantly in old men after the administration of sucrose. Total and non-essential amino acids in the plasma decreased significantly at 120 min after the intakes of glucose in young and old men, but only sucrose caused their decreases in both aged and young men. Both glucose and sucrose intakes decreased significantly the plasma levels of the total essential and branched amino acids in young and old men. Surprisingly, plasma levels of tryptophan did not decrease upon the administration of glucose but only slightly decreased upon the administration of sucrose in young men. In conclusion, not all the amino acids were transported well into tissues upon the administration of glucose or sucrose. Tryptophan seems to be relatively resistant for insulin to facilitate the transportation into tissues.