Pancreatic release of pancreastatin in the pig

It is known that pancreastatin-like immunoreactivity (PLI) occurs in the secretory granules of the islet B- and D-cells in the pig pancreas, and that porcine pancreastatin inhibits insulin secretion in rats and mice. In this study, we characterized the porcine plasma PLI and examined whether PLI is released from the pig pancreas in vivo. We found that PLI in unextracted pig plasma largely consists of two high-molecular fractions, with Mr values of 80-85,000 and 300-350,000, respectively. In addition, a small peak of PLI eluted after gel filtration at the position of synthetic porcine pancreastatin. After extraction on octadecylsilyl silica, virtually all PLI disappeared except in the fraction co-eluting with porcine pancreastatin. In thiopenthal-anesthetized pigs, plasma samples were obtained from the carotid artery and the superior pancreaticoduodenal vein. By multiplying the venous-arterial concentration difference by the pancreatic venous plasma flow, a net pancreatic output of PLI of 420 +/- 120 pmol/min was found. This pancreatic PLI output was significantly reduced by electrical stimulation of the local autonomic nerves along the superior artery during atropine administration (p less than 0.001). Furthermore, the pancreatic venous PLI levels were elevated during intravenous infusion of glucose (p less than 0.01). We conclude that pig plasma PLI levels can be measured by radioimmunoassay after extraction on octadecylsilyl silica and that there is a net pancreatic output of PLI, which is reduced by sympathetic stimulation and enhanced during hyperglycemia.