Besides the structural function in proteins, aromatic amino acids are precursors of many important biological compounds essential for normal functioning of the human organism. Many of these compounds may be used as markers for identification of specific pathological states. Comprehensive knowledge about the metabolism of aromatic amino acids and mechanisms of action of their metabolites made it possible to develop effective treatments for many disorders. However, it should not be forgotten that in some pathological conditions, these compounds could not only be involved in the pathogenesis of many disease entities but could also be used as an important tool in prediction of many diseases. This paper contains a review of published literature on aromatic amino acids in the context of physiological processes of the human body and chosen social disorders, such as cancers; psychiatric disorders: depression, anxiety states, schizophrenia, bipolar affective disorders; neurodegenerative, and cardiovascular diseases; chronic kidney insufficiency or diabetes.
Short fragments of typical or atypical opioid peptides, lacking the whole four amino acid sequence of the enkephalin motif, can preserve a significant percentage of the analgesic activity of the original peptides. This paper investigates the importance of the amino-acidic sequence of minimum structure typical opioid peptides for the analgesic activity. Different groups of rats were treated with 1) Gly-Tyr, 0.5 mg/rat i.t., 2) Tyr-Gly, 0.5 mg/rat i.t., 3) Tyr-Gly-Gly, 0.5 mg/rat i.t., 4) Gly-Gly-Phe-Leu, 0.5 mg/rat i.t., 5) Leu-enkephalin, 0.5 mg/rat i.t.. The analgesic effect of the tested substances was appreciated through the nociceptive threshold for thermal (plantar test) and mechanical nociception (algesimetric test). Fragments of typical opioid peptides elicited antinociceptive activity only when a tyrosine residue was present at the N-terminal end of the amino-acidic sequence. The presence of Nterminal tyrosine provides affinity for the opioid receptors and significant analgesic activity. The intensity of the antinociceptive effect was directly proportional with the length of the amino-acidic sequence. The inhibition of the analgesic effect by previous administration of naloxone proves that this effect is mediated through the opioid system.
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