When female eels, fasting and sexually mature, were progressively adapted to cold water (2–4°C), their blood sugar concentration rose to values averaging 600 mg/dl. Control eels, kept in warm water (18–20°C), had a mean blood sugar concentration of 100 mg/dl. After a period of 5–6 mo, the blood capillaries of the rete mirabile in the swimbladder were examined in both control, low blood sugar eels, and in coldadapted, high blood sugar eels. In the latter, the basal laminae of the capillaries were thickened; their amino acids composition was altered and the in vitro glucose carbon incorporation into basal laminae glycoproteins was increased over a wide range of medium glucose concentrations. Furthermore, the diffusion capacity of the rete, as rqeasured with tracer molecules during steady-state conditions in a countercurrent perfusion system, was increased in the hyperglycemic eel. It is concluded that chronic hyperglycemia in the cold-adapted eel is associated with a microangiopathy characterized by morphologic, biochemical, and functional alterations.

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