SECRETION OF PANCREASTATINS FROM THE PORCINE DIGESTIVE-TRACT

Pancreastatin, a 49-amino acid peptide with a COOH-terminal glycine amide, was originally isolated from porcine pancreas, but pancreastatin immunoreactivity has been found in several neuroendocrine tissues. There are strong indications that pancreastatin is derived from chromogranin A, since the amino acid sequence 240-288 in porcine chromogranin A corresponds to pancreastatin flanked by typical signals for proteolytic processing. We have studied the effect of electric stimulation of the nervous supply to perfused porcine pancreas, antrum, nonantral stomach, and small intestine on the release of immunoreactive pancreastatin, and we characterized the molecular nature of the secreted immunoreactivity by using a radioimmunoassay specific for the COOH-terminal glycine amide of porcine pancreastatin in combination with chromatography. In all tissues nerve stimulation significantly increased the release of immunoreactive pancreastatin. The secreted immunoreactive pancreastatin was heterogeneous, consisting of pancreastatin itself, a COOH-terminal pancreastatin fragment, and NH2-terminally extended pancreastatin forms. Pancreastatin predominated in the perfusate from pancreas and antrum, whereas mainly NH2-terminally extended molecular forms were secreted from the antrectomized stomach and small intestine. The different molecular forms of pancreastatin were secreted from the perfused organs in the same molar ratio as they occur in extracts of the corresponding tissues. Thus, pancreastatin and other chromogranin A-derived peptides in organ-specific proportions regularly accompany the secretion of the peptide hormones from the gastrointestinal tissues on appropiate stimulation.