Secretion of pancreatic icosapeptide from porcine pancreas

The pancreatic polypeptide cell, the only mature endocrine cell in the feta l pig pancreas, produces equimolar amounts of two peptides, pancreatic poly peptide and pancreatic icosapeptide, from the same precursor. The amino aci d sequence of pancreatic polypeptide is more homogenous among species, wher eas pancreatic icosapeptide is heterogeneous. We determined the 19-amino ac id sequence of porcine pancreatic icosapeptide, which is markedly different from that of known sequences (e.g. 47% homology with human). We developed an ELISA that can measure porcine pancreatic icosapeptide levels in the ran ge of 7.2-480 pmol/liter. Actual levels of pancreatic icosapeptide in pig s era were 9.6-25 pmol/liter. The assay requires relatively small amounts of nonextracted samples, and human and mouse sera do not cross-react. Levels o f pancreatic icosapeptide rose in response to hypoglycemia in pigs and to c arbachol in fetal porcine pancreatic cells in vitro. When fetal porcine pan creatic tissue was transplanted into nonobese diabetic-severe combined immu ne deficiency mice, porcine pancreatic icosapeptide (but not C peptide) was detectable in mouse sera for up to 3 wk after transplantation, with levels highest on d 4. Porcine pancreatic icosapeptide and insulin were detectabl e in grafts removed from the mice. Therefore, porcine pancreatic icosapepti de may be used as a marker of the viability of xenotransplanted fetal pig p ancreatic tissue in the immediate posttransplant period.