Mini-reviewAutonomic nervous system and pancreatic islet blood flow
Introduction
Since the original observation of Langerhans, numerous studies have confirmed a rich and dense innervation of endocrine pancreas. Sympathetic (splanchnic nerve) and parasympathetic (vagus nerve) fibres are directly connected to the islets of Langerhans an in such they modulate hormonal secretion and particularly insulin secretion [1], [2], [3].
The autonomic nervous system can also participate to the control of insulin secretion indirectly via the regulation of pancreatic and islet blood flow [4]. This is achieved via 1) the delivery of nutrients and/or other circulating factors involved in the regulation of insulin secretion and 2) the dispersion of insulin itself in the blood stream.
The aim of the present paper is to briefly review data obtained during the last years focusing on both innervation and vascularization of the islet and the role of islet blood flow in insulin secretion in normal and pathological conditions, thanks to new techniques especially imaging one.
Section snippets
Islet innervation and vascularization
Vascularization and innervation of the endocrine pancreas are highly entangled and interconnected and are critical for intercellular and intertissular communication. Although the main effect of the nervous system is the regulation of pancreatic hormones secretion, an important role of parasympathetic activity is the stimulation of endocrine cell proliferation whereas recent data demonstrate the involvement of sympathetic innervation in the islet architecture [5], [6], [7].
Till recently due to
Islet blood flow and influence of the ANS
Islet blood flow is one of the important component of islet activity as assumed and demonstrated by the pioneer observation of Claes Hellerstrom in the sixties and its followers particularly Leif Jansson in the eighties [28], [29]. The techniques used to measure islet blood flow evolved over the years. Starting with quantification by the number of erythrocytes in the islets, flow deposition coupled or not with radiological techniques and since some years various and more and more sophisticated
Changes in pathological conditions
Anatomical studies report remodelling of both microvasculature and innervation in animal models of type 1 and 2 diabetes [26], [32]. As consequence or cause what remains to be demonstrated, there is evidence for dysregulated islet blood flow in metabolic pathologies such as diabetes and/or obesity [14]. Islet hyperperfusion has been reported in most animal models of diabetes and obesity, e.g., obese hyperglycemic (ob/ob) mice [39], lean type 2 diabetic GK rats [40], [41] or after neonatal
Conclusion
More and more data have been accumulated over the years leading to a better understanding of islet morphology and particularly the way they are both vascularized and innervated. However, there are still many shadows that need to be enlightened. Among them one can underline the deciphering of 1) the exact role of the sympathetic nervous system in pancreatic endocrine function; 2) the differences that might exist between animal models and humans; 3) whether dysregulated islet blood flow
Conflict of interest
The author declares no conflict of interest.
Acknowledgments
This work has been made possible by the continuous support of the Centre National de la Recherche Scientifique (CNRS-France).
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