Ultrastructural changes of human cardiac atrial nerve endings in diabetes mellitus

Background Autonomic neuropathy resulting from long-term diabetes mellitus may affect heart innervation. However, so far diabetes induced morphologica l changes of cardiac nerves are not well-known. In this study human cardiac atrial tissue from diabetic patients was analysed by electron microscopy f or structural alterations as a result of diabetic neuropathy. Methods In coronary bypass surgery, an edge of the right auricle was routin ely resected for reason of extracorporal circulation. Thin cardiac tissue s ections of 100 nm were studied by electron microscopy. Atrial tissue sample s were collected from 5 patients with long-standing diabetes (for at least 8 years) and compared to atrial tissue samples from 5 patients without diab etes, equally undergoing coronary bypass surgery. Results In all atria-free nerve endings with unmyelinized, axons were obser ved. Cross sections of 479 axons from diabetic patients were compared to 41 9 axons of nondiabetic patients. The number of altered axons was significan tly higher in cardiac tissue of diabetic patients (32%) in comparison to no rmal subjects (17%). In diabetic patients, 20% of the intra-axonal mitochon dria were condensed or hydropic, whereas in nondiabetic patients only 4% of the mitochondria were altered. Membrane fragments were present in 21% of t he axons in atria of diabetic patients compared to 10% in nondiabetic subje cts. Only in cardiac axons from diabetic patients there were lamellar bodie s, dissolved axoplasma and junctions between neighbouring axons in a minor number. Few vacuoles were present in axons of both groups. Conclusion In myocardial atrial-free nerve fibre bundles of diabetic patien ts, the amount of degenerative changes was higher in comparison to atrial c ardiac tissue from nondiabetic subjects. These morphological alterations ma y indicate manifestation of diabetic neuropathy and might contribute to the impairment of autonomic neural control affecting the heart in long-standin g diabetes mellitus.