IMMUNOHISTOCHEMICAL STUDIES AND SECRETORY EFFECTS OF NEUROPEPTIDES AND REGULATORY PEPTIDES IN THE ISOLATED RAT PANCREAS

This study investigates the distribution and secretory effects of the neuropeptides vasoactive intestinal polypeptide (VIP) and galanin (GAL ) and the pancreatic peptide hormones, glucagon (GLU) and somatostatin (SOMA) in the isolated rat pancreas. The effect of the parasympatheti c neurotransmitter, acetylcholine (ACh) was also studied for compariso n. Immunohistochemical studies identified GLU and SOMA mainly in the p eripheral cells of the islet of Langerhans with the population of GLU was more than double that of SOMA cells. The number of SOMA-immunoreac tive cells per islet ranged from 1-6. GAL and VIP were seen mainly in nerve fibres and cell bodies located in the exocrine part of the pancr eas. Stimulation of isolated pancreatic segments with different concen trations of either GLU, SOMA, VIP, GAL or ACh resulted in differential effects on amylase secretion. Some secretagogue-evoked secretory resp onses consisted of an initial inhibition followed by an elevation in a mylase output depending upon the concentration of the secretagogue. In Fura - 2 acetomethylester (AM) loaded acinar cells, VIP, GAL, GLU and SOMA elicited biphasic changes in intracellular free calcium [Ca2+](i ) concentration with of an initial decrease followed by a gradual incr ease. In the continuous presence of the neuropeptides and peptide horm ones, ACh evoked large increase in [Ca2+](i). The results of this stud y have indicated that the neuropeptides and peptide hormones are prese nt in neural and endocrine cells of the pancreas and they act to mobil ise intracellular Ca2+ which in turn mediates enzyme secretion.