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Existence of the opioid receptors, prohormones and peptides is recorded both in invertebrates and vertebrates. The comparative molecular studies of nucleotide and amino acid sequences rose a hypo- thesis that all opioid prohormones originated by a duplication of proenkephalin gene. Probably, as a first originated proopiomelanocortin, then pronociceptin and after the third and last duplication prodynorphin. Proopiomelanocortin is the prohormon for adrenocorticotropin and melanocyte stimulating hormo- ne, lipotropins and ß-endorphin. From proenkephalin originate leu- and met-enkephalin, met-enkephalin- Arg6-Gly7-Leu8, met-enkephalin-Arg6-Phe7 and peptides E and F. Prodynorphin is a precursor for dynor- phins and neoendorphins. Moreover, in last years atypical opioid peptides (endomorphins, nociceptins, hemorphins and casomorphins) were discovered. Those peptides are the natural ligands for opioid recep- tors. There are four types of opioid receptors: MOR, DOR, KOR and NOR. Comparative analysis of sequence similarities of opioid receptors indicated that they are highly conserved and confirmed supposed evolution order from KOR, trough DOR, till to the youngest MOR receptors. Moreover, it was indicated that in stress conditions animal body could also produce opiates – opioid alkaloids, including morphine.

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The Editorial Board
Andrzej Łukaszyk - przewodniczący, Zofia Bielańska-Osuchowska, Szczepan Biliński, Mieczysław Chorąży, Aleksander Koj, Włodzimierz Korochoda, Leszek Kuźnicki, Aleksandra Stojałowska, Lech Wojtczak

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