Insulin treatment and myocardial function in isolated, perfused heart from diabetic rat

Mitochondria respiration and susceptibility to ischemia-reperfusion injury in diabetic hearts

Cardiovascular complications are the primary cause of death for diabetic patients. Clinical and experimental observation has showed the development of dysfunctional cardiomyopathy as one of the main complications of diabetes. Whether the cardiomyopathy results from an increased susceptibility of cardiac tissue to ischemic insult or from a specific functional defect of cardiac mitochondria is a controversial issue. The investigation of possible functional defect in cardiac mitochondria from diabetic rats indicates a decline in state 3 respiration only in animals presenting a marked decrease in body weight. Mitochondria from rats presenting a level of hyperglycemia similar to diabetic animals but not the marked weight loss typical of the latter group show no decline in state 3 respiration, the values being indistinguishable from those of control mitochondria. Mitochondria from hyperglycemic rats, however, show a 15-20% increase in state 4 oxygen consumption but only when glutamate is used as energetic substrate, as compared to a 40-50% increase in state 4 respiration in mitochondria from diabetic rats under similar experimental conditions. This phenomenon is unrelated to diabetes duration, as it is observed at 2 as well as 8 weeks after diabetes onset. Taken together, these data argue against hyperglycemia per se being a direct cause of the decline in state 3 oxygen consumption observed in cardiac mitochondria of type-I diabetic rats and indicate that differences exist in cardiac mitochondrial function in rats generically labeled as diabetic. These differences can contribute to explain discrepancies in experimental results reported by various groups in the field and provide an additional parameter to be taken into consideration in evaluating the varying sensitivity of diabetic hearts to ischemia-reperfusion injury.

Role of the sodium-hydrogen exchanger in ischemia-reperfusion injury in diabetes

Ischemic heart disease is a significant problem in the diabetic population. Animal models of diabetes show a paradoxical resistance to ischemic challenge. The present treatise will discuss the mechanics involved and the central role that Na+-H+ exchanger plays in this response to ischemic-reperfusion injury.

Effects of norepinephrine on hypoperfusion-reperfusion injuries in hearts isolated from normal and diabetic rats

Contractile and energy-metabolic functions were investigated in paced hearts isolated from normal (Normal) and streptozotocin-diabetic rats (DM) during hypoperfusion at 1 ml/min with or without 10(-6) M norepinephrine (NE) and during reperfusion at the pre-hypoperfusion flow. Left ventricular pressure (LVP) and contractile force (CF) were monitored, respectively, through a water-filled balloon in LV and through a hook attached to the apex. A 1-h hypoperfusion without NE caused significant elevations in resting LVP and resting CF only in DM hearts, smaller transmural lactate accumulations in DM hearts, and similar ATP decreases in both groups. Significant decreases in developed LVP and developed CF were observed in both groups. NE during hypoperfusion caused deterioration of these cardiac dysfunctions in both groups, particularly in DM hearts. A 1-h reperfusion caused elevations in resting LVP and resting CF with no recovery in developed CF in Normal hearts, while it caused partial recovery in resting and developed CF in DM hearts. Both groups showed similar partial recovery of ATP. NE during hypoperfusion improved the mechanical dysfunction during reperfusion in DM hearts, but there was a smaller recovery in ATP than in hearts without NE. In vivo insulin treatment in DM restored the cardiac functions to Normal levels. Thus, DM hearts were more vulnerable to hypoperfusion, while Normal hearts were more vulnerable to reperfusion injury.

Effects of alloxan-induced diabetes on ischemia-reperfusion injury in rabbit hearts

Hearts from rabbits with 8-16 weeks of alloxan-diabetes were compared with hearts from normal rabbits to determine whether diabetic myocardium is more sensitive to ischemic injury. In isolated buffer-perfused hearts, left ventricular developed pressure, diastolic pressure, time to peak pressure (TTPP), time to half-maximal relaxation (RT1/2), and positive and negative dP/dt were measured during generation of left ventricular filling curves before and after 90 minutes of low-flow ischemia. Hearts from diabetic rabbits (blood glucose, 384 +/- 28 mg/dl, mean +/- 95% confidence limits) had left ventricular developed and diastolic pressures similar to normal hearts but exhibited significant increases in TTPP and RT1/2 with decreased positive and negative dP/dt. Left ventricular chamber volume relative to heart mass was greater in diabetic than in normal hearts. Recovery of developed pressure after ischemia was similar in normal (41 +/- 16%) and diabetic hearts (47 +/- 13%). In diabetic hearts during recovery from ischemia, TTPP and R1/2 remained increased compared with normal hearts, with positive and negative dP/dt decreased compared with normal hearts, in proportion to the preischemic differences. After ischemia, high-energy phosphates were depleted to the same extent in normal and diabetic rabbits. In coronary ligation experiments, histochemically determined infarct size in diabetic rabbits after 30 minutes occlusion and 24 hours reperfusion was similar to that in normal rabbits when adjusted for a significantly smaller heart weight and a correspondingly smaller anatomic risk region in the diabetic animals. Thus, despite characteristic abnormalities of mechanical function in diabetic hearts, the severity of injury after ischemia with reperfusion was normal for diabetic hearts.