THE RETE-MIRABILE OF THE EEL - A UNIQUE M ODEL FOR THE STUDY OF MICROVASCULAR PERMEABILITY

The rete mirabile of the eel swim-bladder is a countercurrent perfused microvascular organ made of alternating arterial and venous capillari es which function as gas exchangers in order to maintain fish buoyancy . The organ offers the unique opportunity to allow for the simultaneou s study of its morphology, biochemistry and function and for the relia ble measurements of capillary permeability to substances with a wide r ange of molecular weights. The ultrastructure of the capillaries is si milar to that of mammalian capillaries. Large quantities of capillarie s can be isolated and incubated in vitro : their energy metabolism is glucose dependent and insulin insensitive. The sorbital pathway and ba sal lamina non-enzymatic glycosylation are very responsive to the ambi ent glucose concentration. The permeability of the rete capillaries to tracers varying in size, charge, and lipid solubility reveals differe nt 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 mi croangiopathy of the rete capillaries characterized by basal lamina th ickening and increased permeability. The model could prove useful for the study of the mechanisms responsible for the progression and eventu al regression of the diabetic microangiopathy.