Diabetes as a Paracrinopathy of the Islets of Langerhans

The small clusters of cells scattered in the pancreas and discovered by Langerhans in 1869, currently known as the islets of Langerhans, are at the centre of the pathology of diabetes. Today they appear as sophisticated micro-organs in which various cell types function in a remarkably co-ordinated manner. Until recently, most of the interest has been centred on the β-cells, which synthesise, store and secrete insulin. Insulin deficiency is the hallmark of diabetes, with insulin resistance being associated with some forms of the disease. Although identified more than 40 years ago, a possible role of glucagon in the pathophysiology of diabetes has been largely neglected. Synthesised, stored and released by the α-cells of the islets of Langerhans, glucagon plays a key role in the main metabolic disturbances of diabetes that are hyperglycaemia and excessive lipolysis and ketogenesis. Suggested by Samols et al. decades ago, the possibility of close interactions between αand β-cells within the islets of Langerhans has recently received considerable experimental support. Unger and Orci have proposed that such paracrine interactions within the pancreatic islets play a crucial role in a vital homoeostatic domain and that disruption or dysfunction of these interactions has to be considered as a key component in the pathophysiology of diabetes. This brief article will present arguments supporting the view of diabetes as a paracrinopathy of the islets of Langerhans.