Autonomic insulin secretion

The first glucose sensors to be discovered were the pancreatic -cells in the islets of Langerhans these manufacture the hormone insulin and release it into the blood when glucose concentration rises. Islet tissue also contains a-cells, which manufacture the antagonistic hormone glucagon. Insulin secretion is a complex process, and the islet cells receive additional signals from the gut and the autonomic nervous system, which modulate the insulin release to match the food that has been eaten. 

Introduction. It is well-known that the hypothalamus participates in the regulation of carbohydrate metabolism via the autonomic nervous system. As far as the secretion of insulin is concerned, vagal stimulation causes release of insulin whereas adrenergic stimulation is inhibitory. Moreover, in addition to the classical neurotransmitters, neuropeptides present in the efferent autonomic nerves (GRP, VIP, peptide histidine-isoleucinamide (PHI), neuropeptide Y (NPY), CCK, galanin) are also of importance. The subject has previously been reviewed by Holst (1992). The existence of a cephalic phase of insulin secretion, i.e. reflex-stimulated secretion, has been well established in rats (Strubbe and Steffens, 1975), and there is also evidence for a cephalic-phase insulin response in humans (Bruce et al., 1987 Loud et al., 1988). 

The naturally mediated inhibition of insulin secretion in response to hypoglycaemia is probably elicited after activation of cerebral glucosecep-tors (Rohner-Jeanrenaud et al., 1983) and through central noradrenergic pathways (McCaleb and Myers, 1982). The nerve fibres that enter the pancreas are mixed nerves (i.e. sympathetic and parasympathetic) derived from the splanchnic area and the N. vagus. These nerves generally accompany the superior pancreatic-duodenal vessels. Autonomic nerves have their terminals in close proximity to A- and B-cells (Ahren et al., 1986). 

As biomolecule-responsive hydrogels that undergo changes in volume by the changes in physicochemical properties of polymer backbone, there are glucose-responsive hydrogels for a potential autonomous treatment of insulin-dependent diabetes mellitus (IDDM). Insulin is a hormone secreted from the Langerhans islets of the pancreas... 

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