Quantitation and localization of Met-enkephalin-Arg-Gly-Leu in rat brain using highly sensitive antibodies.

Met-enkephalin-Arg-Gly-Leu is an endogenous opioid peptide recently identified in bovine adrenal medulla. In the present study, we describe the production of highly sensitive and specific antibodies against this octapeptide. The sensibility of the radioimmunoassay procedure allows us to quantify at the femtomole level, the Met-enkephalin-Arg-Gly-Leu in individual parts of the brain without prior purification or concentration. The antibodies are highly specific for the C terminal part of the molecule, and did not cross-react with the other opioid peptides. Immunochemical techniques were used also to determine the histological location of the immunoreactive substances in individual structures of the brain. In the present paper, the comparative regional distribution of Met-enkephalin-Arg-Gly-Leu and of Met-enkephalin in rat brain are described. Our results are in good agreement with the biosynthetic relationship between Met-enkephalin and Met-enkephalin-Arg-Gly-Leu.