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Neural control of the endocrine pancreas

Neural control of the endocrine pancreas - Neural control...

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Neural control of the endocrine pancreas By DAVID R . MATTHEWaSn d ANNE CLARK D , iabetes Research Laboratories, It has been known from the 19th century that the pancreas is innervated. In his doctoral thesis Langerhans (1869) noted that the ‘Zellhaufen’ or clusters of cells, which he observed and which were later called the Islets of Langerhans had certain connections with the nervous system. There was of course, at this stage, no evidence for the function of these islets. Earlier Bernard (1849) had made an important physiological observation that lesions made at the base of the fourthventricle in dogs resulted in glycosuria. Thus both anatomical and physiologicalclues about the innervation of the pancreas have been recognized for more than a century. Advances in understanding the importance of the innervation of the pancreas has, however, been slow, due to the fact that, after the isolation of insulin, it became evident that insulin release was regulated largely by blood glucose levels and there seemed no compelling reason to investigate neural control. It remains true that in the whole animal, in the perfused pancreas (Samols & Weir, 1979), or even in isolated islets (Ashcroft, 1980), that glucose and many other substrates can be a sufficient stimulus for insulin release. Neural inputs to the pancreas are therefore modulating rather than initiating influences but their importance should not be underestimated. Anatomical evidence Parasympathetic fibres of the vagus and sympathetic nerves from the splanchnic trunk innervate the pancreas, and nerve networks can be seen adjacent to some islets (Plate I). However, there is sparse ultrastructural evidence for a functional continuity between the nerves and the endocrine cells. Peptidergic neurones containing vaso-active intestinal polypeptide (VIP) (Bishop et al. 1980), substance-P, enkephalin and gastrin-cholecystokinin (CCK) (Larsson, I 979) have been identified by immunocytochemistry. Although dense networks of VIP-containing fibres surround the islets, peptidergic nerves are also associated with numerous ganglia found throughout the pancreas (Bishop et al. 1980). These ganglia may be areas of integration of extrinsic and intrinsic nerve signals, and may even be the sites of initiation of pulsatile hormone secretion (Stagner & Samols, 1985). Physiological studies on pancreatic secretion Insulin and glucagon. The studies of Frohman et al. (1967) were a marked step forward in our understanding of the importance of the pancreatic innervation.
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