Distribution of adrenomedullin (AM), proadrenomedullin N-terminal 20 peptide, and AM mRNA in the rat gastric mucosa by immunocytochemistry and in situ hybridization

Adrenomedullin (AM) is a novel vasorelaxant peptide isolated from pheochrom ocytoma. Proadrenomedullin N-terminal 20 peptide (PAMP) is a hypotensive pe ptide generated by posttranslational enzymatic processing of a 185-amino ac id pro-AM molecule, the same precursor as AM. In this study, we investigate d localizations of these peptides by immunocytochemistry and AM mRNA by non -radioisotopic in situ hybridization followed by the streptavidin and bioti n complex (ABC) method and catalyzed signal amplification (CSA) in the rat adrenal medulla and gastric mucosa. In the gastric mucosa, both AM- and PAM P-like immunoreactivities were found in the neuroendocrine cells, but PAMP- positive cells were more abundant than AM-positive ones. By immunoelectron microscopy, AM and PAMP were localized exclusively in the secretory granule s. The distribution pattern of AM mRNA-positive cells, only a limited porti on of which had AM and/or PAMP, was also similar to that of the two peptide s. But AM mRNA was detected also in a few epithelial cells as well as neuro endocrine cells. The two peptides might play an important role in the contr ol of local circulation in the rat stomach.