The distribution of porcine pancreatic beta-cells at ages 5, 12 and 24 weeks.

Islet transplantation is a potential treatment for diabetes mellitus and porcine pancreata may provide a readily available source of islets. The size, number and distribution of islets within the pancreas may influence the choice of age of donor for xenotransplantation. Samples (n = 3 per age group) from the dorsal and ventral pancreas of 5-, 12- and 24-week-old hybrid pigs were fixed in formal saline, processed in paraffin wax and stained with an avidin/biotin immunohistochemical kit for insulin, glucagon, somatostatin and pancreatic polypeptide. The arrangement of endocrine cells within the pancreata were studied and mean diameter of beta-cell groups were measured (from insulin stained sections) in 1 mm2 grid areas (n = 10 per section) and collated into groups according to size. Percentage volume density of beta-cells in relation to the whole pancreas was calculated and also the distribution of beta-cell groups, according to their size, within the total beta-cell mass. There were differences in the frequency and arrangement of endocrine cells within islets at the different ages studied. beta-Cell groups < 50 microm in diameter occupied 70 to 80% of the total beta-cell mass at 5 weeks but, as the age of the pig increased, larger cell groups were more abundant. However, the percentage volume density of beta-cells within the total pancreas did not change as the pancreas matured. This study shows that the endocrine porcine pancreas was maturing and its structure changed between the ages of 5 and 24 weeks. The relevance of these findings may have implications on the isolation and function of islets if young pigs are to be used as donors for transplantation as a treatment for diabetes mellitus.

Expression of the GALalpha(1-3)GAL epitope on pig islets.

Expression of Galalpha(1-3)Gal on endothelium has been implicated in the rejection of porcine xenografts. The aim of this study was to determine whether expression of Galalpha(1-3)Gal on pig islets varies between pigs aged 5, 12 and 24 weeks, and to investigate whether it is expressed on islets isolated by collagenase digestion or islets maintained in tissue culture. Samples of pancreas were obtained from pigs aged 5, 12 and 24 weeks. Islets were isolated by manual collagenase digestion and density gradient separation. Samples were taken immediately after isolation or after maintenance in tissue culture. Pancreas and islet samples were processed, sectioned and stained with the lectin BS1-B4 (which binds to Galalpha(1-3)Gal residues), and anti-insulin antibody using a double staining technique. There was no significant difference in the staining patterns to sections of pancreas obtained from 5, 12 and 24 week old pigs. Vascular endothelium, connective tissue and the luminal surface of duct epithelial cells stained with BS1-B4 in all sections; endocrine and exocrine cells did not stain. Preliminary experiments showed that lectin staining to isolated islets was inconsistent between preparations, but expression did not appear to differ significantly between ages: lectin staining of some beta-cells was evident in the majority of freshly isolated preparations, but was not detectable on beta-cells following tissue culture. In conclusion, expression of Galalpha(1-3)Gal did not differ significantly in pancreata from 5, 12 and 24 week old pigs. Preliminary experiments showed that Galalpha(1-3)Gal was expressed by beta-cells immediately following isolation, but not after maintenance in culture.