Effect of experimental non-insulin requiring diabetes on myocardial microcirculation during ischaemia in dogs

To examine whether chronic high blood glucose may influence myocardial microcirculation during acute myocardial ischaemia in the dog, a noninsulin-requiring diabetes was induced by the streptozotocin-alloxan method. Seventy-five days later, myocardial ischaemia was provoked by occluding the left anterior descending coronary artery for 2 h and microcirculation regulation was assessed in the ischaemic and non-ischaemic myocardium by the radioactive microsphere method. Diabetic dogs were compared with normal dogs. Diabetic dogs had higher blood glycated haemoglobin (2.66 +/- 0.4%) and fructosamine (397 +/- 62 mumol l-1) than control dogs (0.66 +/- 0.2, P < 0.004 and 229 +/- 13, P < 0.03, respectively). Haemodynamic data in the two groups were not different at any time. The size of the ischaemic zone was similar in both groups. During the 2 h ischaemia in the ischaemic zone subendocardial (P = 0.22) and subepicardial (P < 0.05) blood flow slightly increased in control dogs whereas there was a 63% (P < 0.02) and 35% (P = 0.06) reduction respectively in diabetic dogs. In the non-ischaemic zone, blood flow of controls tended to increase (P < 0.006 in the subepicardium and P < 0.06 in the subendocardium) whereas in diabetic dogs blood flow tended to decrease (P = 0.03 in the subendocardium and in the subepicardium). This first investigation on myocardial microcirculation in diabetic dogs during ischaemia suggests that one of the possible causes of increased mortality rate from ischaemic cardiac disease in diabetics might be related to a paradoxical and unfavourable pattern of myocardial blood flow during ischaemia.