ANGIOTENSIN-II AND THE ENDOCRINE PANCREAS - EFFECTS ON ISLET BLOOD-FLOW AND INSULIN-SECRETION IN RATS

An intrinsic angiotensin system has been described in the pancreas, wi th angiotensin II specific receptors being present on both exocrine, e ndocrine and vascular cells. The aim of the present study was to evalu ate the effects of angiotensin II on insulin secretion and blood flow regulation in the pancreas. Blood flows were determined with a microsp here technique. Infusion of angiotensin II induced a dose-dependent re duction in both whole pancreatic and islet blood flow, which was most pronounced in the former. Administration of enalaprilate, an inhibitor of angiotensin-converting enzyme, and saralasin, a nonselective angio tensin II receptor antagonist, preferentially increased islet blood fl ow. The effects of angiotensin II on insulin release were examined by measuring insulin concentrations in the effluents from isolated perfus ed pancreata. In these preparations, enalaprilate affected neither bas al nor glucose-stimulated insulin release, whereas angiotensin II dela yed the first phase of insulin release in response to glucose. The eff ect of angiotensin II was probably due to initial marked vasoconstrict ion. The retardation of insulin release could be avoided by adding ang iotensin II to the perfusion medium 20 min before glucose administrati on, i.e. so that the vasoconstriction had disappeared when glucose-sti mulation began. The present study suggests that the angiotensin-system is important in regulation of islet blood flow and points to a pivota l role of islet blood perfusion for an adequate insulin release.