Ontogeny of salivary peptide P-C like immunoreactivity in human pancreatic B-cells

Abstract

Abstract. An immunohistochemical study using antisera against proline rich salivary peptide P-C and insulin, glucagon, somatostatin and pancreatic polypeptide antisera was carried out on the foetal pancreas at different stages and on the newborn infant's, infant's, child's and adult pancreas to examine the time at which salivary peptide P-C like immunoreactivity appeared in the human pancreas. Salivary peptide P-C like immunoreactive cells first appeared as a few scattered cells in the foetal pancreas after 16 weeks of gestation and gradually increased in numbers during gestation. The cells corresponded only to insulin immunoreactive cells in the foetal, newborn infant's, infant's, child's and adult pancreas. Only some of the insulin immunoreactive cells in the foetal pancreas contained salivary peptide P-C like immunoreactivity while the majority of those in the infant's pancreas and all those in the child's and adult pancreas did so. The findings, together with the fact that the full sequence of salivary peptide P-C is identical to the COOH-terminal 44 amino acid residues of Salivary Protein C, led to the possibility that peptide P-C like immunoreactivity in the human pancreatic B-cells was not a moiety of the precursor of insulin and pro-insulin, but a moiety of Salivary Protein C. It has been suggested that, in saliva, Salivary Protein C aids in maintenance of the calcium concentration. Based on the hypothesis that peptide P-C like immunoreactivity in the human pancreatic B-cells may play some role in insulin release through the maintenance of the calcium concentration, the present finding seems to explain the fact that the mechanism for insulin release in the foetal pancreas is immature in spite of sufficient biosynthesis of insulin.