Distribution and molecular forms of adrenomedullin and proadrenomedullin N-terminal 20 peptide in the porcine gastrointestinal tract.

Adrenomedullin (AM) and proadrenomedullin N-terminal 20 peptide (PAMP) are potent hypotensive peptides that are generated from the same precursor and expressed in a variety of mammalian tissues. The purpose of this study was to elucidate the distribution and endogenous molecular forms of AM and PAMP. To this end, we used new radioimmunoassays that recognize the ring structure of AM and the C-terminal region of PAMP to compare the distribution of AM and PAMP in porcine gastrointestinal tissues. Immunoreactive AM was abundant in the duodenum (0.334+/-0.132 fmol/mg) and ileum (0.439+/-0.235 fmol/mg), and ubiquitous in other gastrointestinal tissues. The duodenal and ileal concentrations of AM were about 4 to 14 times higher than those in other gastrointestinal tissues. Similarly, immunoreactive PAMP was abundant in the duodenum (0.577+/-0.417 fmol/mg) and ileum (1.575+/-1.445 fmol/mg) and ubiquitous in other gastrointestinal tissues. The concentrations of immunoreactive AM and PAMP were highest in the ileum. Characterization of these peptides in the ileum, using high-performance liquid chromatography, showed that they were authentic. Furthermore, the concentrations of immunoreactive AM and PAMP in the mucosa and submucosa of the ileum were significantly higher than those in whole ileum. These results suggest that AM and PAMP play physiological roles in the porcine small intestine.