Calcitonin gene-related peptide and somatostatin inhibit insulin release from individual rat B cells.

Hormone secretion from single, rat pancreatic B cells was visualised by a reverse haemolytic plaque assay for C-peptide. Quantitative analysis of the size and number of haemolytic plaques indicated that exposure to 3, 5, 10 and 20 mM glucose resulted in a dose-dependent increase in both the magnitude of C-peptide, and thus, insulin release by individual B cells and the recruitment of activity secreting B cells. Somatostatin and calcitonin gene-related peptide, fragment 28-37 (CGRP28-37) were shown to inhibit glucose-stimulated insulin release as assessed by the size of individual plaques and the number of recruited B cells, and hence to reduce the total area of plaques formed. In the presence of 15 mM glucose, a dose-dependent effect of CGRP28-37 on the secretion of insulin was observed, with the size of plaques formed by individual B cells reduced at concentrations of CGRP28-37 between 10(-5) and 10(-11) M. Thus, both somatostatin and CGRP28-37 can act directly on individual B cells to inhibit their secretory response to increasing levels of glucose. We suggest that these peptides which can be immunolocalised in islet cells may have a role in the regulation of insulin secretion.