Impact of the COMT Val108/158Met polymorphism on the mu-opioid receptor system in the human brain: Mu-opioid receptor, met-enkephalin and beta-endorphin expression

► MOP receptor levels are significantly influenced by COMT Val108/158Met genotypes. ► Enkephalin peptide levels also indicate a genotype-dependent expression. ► Beta-endorphin is unlikely to contribute to changes of the MOP receptor system. ► The results support the hypothesis of an enkephalin related MOP receptor turnover.