LOCALIZATION OF AMIDATING ENZYMES (PAM) IN RAT GASTROINTESTINAL-TRACT

We studied the distribution of the two enzymes involved in post-transl ational C-terminal alpha-amidation of regulatory peptides in rat diges tive tract, using immunocytochemical methods and in situ hybridization techniques. The enzymes were located in most of the fibers and neuron s of the myenteric and submucous plexus throughout the entire digestiv e tract and in endocrine cells of the stomach and colon. Staining of r everse-face serial sections demonstrated that the enzymes in endocrine cells of the stomach co-localized with gastrin in the bottom of the g astric glands. Some gastrin-immunoreactive cells near the neck of the gland were negative for PAM, suggesting that amidation takes place onl y in the more mature cells. In the colon all cells immunoreactive for glucagon and GLP1 were also positive for peptidylglycine alpha-hydroxy lating monooxygenase (PHM) but not for peptidyl-alpha-hydroxyglycine a lpha-amidating lyase (PAL). The absence of immunoreactivity for the am idating enzymes in endocrine cells of the small intestine, known to pr oduce C-terminally amidated peptides, suggests the existence of other amidating enzymes.