Effect of adrenergic and cholinergic agonists on vasoactive intestinal polypeptide release from pancreatic islets of normal and diabetic rats

Background and aims: Vasoactive intestinal polypeptide (VIP) is present in pancreatic islet cells and stimulates insulin and glucagon release from normal and diabetic rats. The aim of this study was to examine the effect of noradrenaline (NA) and acetylcholine (ACh) on VIP release from pancreatic islets of normal and diabetic rats. Methods: NA- and ACh-induced VIP release from isolated pancreatic tissue fragments was measured using radioimmunoassay technique. Results: The basal VIP release from the islets of diabetic rats was significantly (p = 0.02) higher compared to normal, NA at and 10^-6 m also evoked large and significant (p = 0.04) increases in VIP release from the islets of normal rat. Moreover, NA at 10^-8 M, significantly (p < 0.05) stimulated VIP release from the islets of diabetic rats. ACh (10^-4 M), induced up to 46.6% increase in VIP secretion from the islet cells of normal (n = 6) rats. However, a more dilute concentration of ACh (10^-8 M) was sufficient for the induction of maximal VIP secretion from the isolated islets of diabetic (n = 6) rat. ACh (10^-6 M) evoked 32.3% increase in VIP secretion in diabetic rat islets. Conclusion: NA and ACh stimulated VIP secretion from pancreatic islets of normal rat. NA and ACh can also induce increases in VIP secretion from the islets of diabetic rat. The increase in VIP in the islets of diabetic rats may also play a role in the pathogenesis of diabetic complications.