Immunohistochemistry of Chromogranin A and B, and Secretogranin II in the Canine Endocrine Pancreas

The chromogranins are large acidic proteins contained in secretion granules of adrenal medullary cells. These proteins are also presumed to be regular constituents of other endocrine cells, e. g., pancreatic endocrine cells. In our previous immunohistochemical studies performed in the endocrine pancreas of 10 mammalian species, only canine endocrine cells lacked any immunoreactivity for chromogranin A. Therefore, this problem was reinvestigated in the present study. Antisera against bovine and rat chromogranin A, B, and C (=secretogranin II) were applied under various conditions of the immunohistochemical protocol. Upon meeting certain requirements, chromogranin-immunoreactivities were found also in canine pancreatic B- (insulin), PP- (pancreatic polypeptide), and EC- (enterochromaffin) cells. The immunohistochemical data suggest that canine chromogranins partially differ structurally or immunologically from bovine chromogranins and completely from rat chromogranins. In addition, the present findings confirm our previous findings about both interspecies differences in the cellular localization of chromogranins in the endocrine pancreas and the peculiar localization of secretogranin II to pancreatic PP-cells. Finally, the present methodological studies have shown that even the buffer used in the immunohisto-chemical protocol may be decisive for a false-positive or false-negative immunostaining.