Le rete-mirabile de l'anguille, un modèle unique pour l'étude de la perméabilité capillaire
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The rete mirabile of the eel swim-bladder is a countercurrent perfused microvascular organ made of alternating arterial and venous capillaries which function as gas exchangers in order to maintain fish buoyancy. The organ offers the unique opportunity to allow for the simultaneous study of its morphology, biochemistry and function and for the reliable measurements of capillary permeability to substances with a wide range of molecular weights. The ultrastructure of the capillaries is similar to that of mammalian capillaries. Large quantities of capillaries can be isolated and incubated in vitro : their energy metabolism is glucose dependent and insulin insensitive. The sorbital pathway and basal lamina non-enzymatic glycosylation are very responsive to the ambient glucose concentration. The permeability of the rete capillaries to tracers varying in size, charge, and lipid solubility reveals different paths of transport which can be independently influenced by physico-chemical agents, such as temperature, osmolality and hypoxia. Chronic hyperglycemia, induced in the eel by cold adaptation, results in a microangiopathy of the rete capillaries characterized by basal lamina thickening and increased permeability. The model could prove useful for the study of the mechanisms responsible for the progression and eventual regression of the diabetic microangiopathy.