The pancreatic polypeptide cell, the only mature endocrine cell in the fetal pig pancreas, produces equimolar amounts of two
peptides,
pancreatic polypeptide and
pancreatic icosapeptide, from the same precursor. The amino acid sequence of
pancreatic polypeptide is more homogeneous among species, whereas
pancreatic icosapeptide is heterogeneous. We determined the 19-amino
acid 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 range of 7.2-480 pmol/liter. Actual levels of
pancreatic icosapeptide in pig sera 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 of
pancreatic icosapeptide rose in response to
hypoglycemia in pigs and to
carbachol in fetal porcine pancreatic cells in vitro. When fetal porcine pancreatic tissue was transplanted into nonobese diabetic-
severe combined immune 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 detectable in grafts removed from the mice. Therefore, porcine
pancreatic icosapeptide may be used as a marker of the viability of xenotransplanted fetal pig pancreatic tissue in the immediate posttransplant period.