Reduction by cobra venom factor of myocardial necrosis after coronary artery occlusion.

Components of the complement system are known to play an important role in the cytolytic process and in chemotaxis of leukocytes. Cobra venom factor specifically cleaves C3 activity via activation of the alternative (properdin) complement pathway. It does not act directly on C3. If C3 is involved in tissue necrosis after ischemic injury, cobra venom factor might reduce tissue damage after acute coronary occlusion. Accordingly, in 14 control dogs occlusion of the left anterior descending artery was carried out for 24 h. Epicardial electrograms were recorded 15 min after occlusion, and 24 h later transmural specimens for creatine phosphokinase activity (CPK) and for histological analysis were obtained from the same sites. In another 14 experimental dogs, 20 U/kg cobra venom factor was given intravenously 30 min after occlusion. Serum complement levels fell within 2-4 h to <20% of normal. In the control dogs, the relationship between ST-segment elevation and CPK activity 24 h later was: log CPK = -0.06 ST + 1.48 (n = 111 specimens, 14 dogs, r = 0.77). In the experimental dogs, log CPK = -0.024 ST + 1.46 (n = 111 specimens, 14 dogs, r = 0.60), showing significantly different slopes (P < 0.001), i.e., less CPK depression for any level of ST-segment elevation. Histologically, 69 of 71 sites (97%) with ST-segment elevation exceeding 2 mV in the control dogs showed signs of necrosis 24 h later, whereas in the experimental group only 43 of 79 sites (54%) with abnormal ST-segment elevations showed signs of necrosis (P < 0.0005). At the same time, it was shown that the administration of cobra venom factor did not alter cardiac performance, collateral blood flow to the ischemic myocardium or the clotting system, but infiltration of polymorphonuclear leukocytes into the myocardium was decreased. It is concluded that cobra venom factor, by reducing the amount of C3 and C5 substrate available for chemotactic factor generation, or other as yet undefined mechanisms, protects the ischemic myocardium from undergoing necrosis, as judged by histology and local CPK activity. Hence, a new approach to limiting the extent of myocardial infarcts after experimental coronary occlusion, based upon inhibition of complement-dependent inflammatory processes, is demonstrated.

Hypothermic, closed circuit pericardioperfusion: a potential cardioprotective technique in acute regional ischemia.

OBJECTIVES: This study sought to determine whether infarct size can be reduced by hypothermic pericardioperfusion. BACKGROUND: We have shown that myocardial infarct size can be reduced by topical cooling of the heart. The present study tests whether myocardial cooling and protection can be produced by hypothermic pericardioperfusion using a catheter. METHODS: The catheter was sutured into the pericardial space of anesthetized rabbits. Beginning 30 min before coronary artery occlusion, the space was perfused with either chilled (n = 10) or body temperature (n = 10) fluid. The artery was occluded for 30 min and reperfused for 3 h. RESULTS: After 30 min of pericardioperfusion, myocardial temperature was reduced to 34.1 +/- 0.9 degrees C in chilled hearts compared with 38.9 +/- 0.4 degrees C in control hearts, p < 0.001, a reduction in myocardial temperature of approximately 5 degrees C. Risk areas were similar in both groups (32 +/- 4% left ventricle in cooled and 31 +/- 3% in control hearts, p = NS). However, infarct size in cooled hearts was significantly reduced by 49% (18 +/- 3% of risk area vs. 35 +/- 6%, p = 0.025). Tamponade did not develop, and there were no significant differences in heart rate, arterial pressure or body temperature between groups. CONCLUSIONS: A significant reduction in myocardial temperature, without the development of cardiac tamponade, can be attained using a pericardial catheter to cool the pericardial space. This reduction in temperature causes a significant reduction in necrotic damage. This technique might be used to cool and protect the heart as an adjunct to thrombolysis or during minimally invasive cardiac surgery.

Myocardial temperature reduction attenuates necrosis after prolonged ischemia in rabbits.

OBJECTIVE: Previously we observed that a large reduction in infarct size was attained by cooling the risk region of the heart, either before or early after the onset of a 30-min coronary artery occlusion. While this is a standard duration of ischemia used in the rabbit model of infarction, it may not reflect the situation of patients who are reperfused late. The effects of regional hypothermia with a longer duration of ischemia, and when the intervention is applied later, are unknown. This study tests the hypothesis that a local reduction in cardiac temperature protects myocardium during prolonged ischemia (2 h) even if begun well after coronary artery occlusion. METHODS: Anesthetized rabbits received 2 h of coronary artery occlusion and 3 h of reperfusion. Rabbits were randomly assigned to a treated group: topical myocardial cooling starting 30 min after coronary occlusion (n = 14), or control group, no intervention (n = 12). Myocardial temperature in the risk zone, hemodynamics and regional myocardial blood flow were measured. RESULTS: Ischemic zone temperature was similar in both groups at 30 min post occlusion, but the cooling maneuver produced a reduction in temperature in the risk region of the treated group such that myocardial temperature was reduced an average of 10 degrees C between 30 and 60 min of coronary artery occlusion. Myocardial temperature in the control group remained within 0.3 degree C of baseline during coronary artery occlusion and into reperfusion. Core temperatures were similar in both groups. Hemodynamic parameters and collateral blood flow during occlusion were also equivalent in both groups. After 120 min of coronary occlusion, necrosis in the control group comprised 72 +/- 3% of the ischemic risk region. However, in cooled hearts, infarct size, expressed as a fraction of the risk region was significantly lower. Infarct size in this group averaged 59 +/- 3% of the risk region (p < 0.004 vs. controls), and thus cooling resulted in a salvage of approximately 18% of the risk region. CONCLUSION: These results show that reducing myocardial temperature protects ischemic myocardium during a long duration of ischemia even if initiated after coronary artery occlusion.

Effect of early coronary artery reperfusion on infarct development in a model of low collateral flow.

To characterise collateral blood flow patterns after coronary artery occlusion in the rat and to determine whether tissue can be salvaged by reperfusion in this model, anaesthetised rats were subjected to 20, 30, 40, 60 min of coronary occlusion followed by 24 h of reperfusion or 24 h of permanent occlusion. Relative regional blood flow was measured by radioactive microspheres after 10 min of occlusion in rats undergoing 30 min of occlusion plus reperfusion and in those undergoing 24 h of permanent occlusion. The area at risk was determined by in vivo injection of fluorescent microspheres and necrosis delineated by in vitro tetrazolium staining. Tracings of heart slices were planimetered and the area of necrosis and transmural extent of the infarct measured. Blood flow in the area at risk during occlusion was similar in both the reperfused and permanent occlusion groups. In the 30 min group mean(SEM) subendocardial flow was reduced to 13(5)% of normal and subepicardial flow to 9(3)% and in the permanent occlusion group to 11(2)% and 8(3)% respectively. As delineated by fluorescent microspheres the area at risk was transmural in all rats; however, infarct size expressed as a percentage of the area at risk increased as the duration of occlusion increased. In rats reperfused up to 30 min after occlusion the area of necrosis as a percentage of the area at risk was significantly decreased compared with that in the permanent occlusion group (36.4(9.2)% in rats with 30 min occlusion plus 24 h reperfusion and 78.6(7.4)% in rats with permanent occlusion).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of coenzyme Q10 on infarct size in a rabbit model of ischemia/reperfusion.

OBJECTIVE: Coenzyme Q10 has been found to enhance recovery of function after reperfusion in numerous experimental acute ischemia-reperfusion models. We assessed whether coenzyme Q10, administered intravenously either during or 1 h before ischemia, can limit infarct size in the rabbit. METHODS: Anesthetized open-chest rabbits were subjected to 30 min of coronary artery occlusion and 4 h of reperfusion. In Protocol 1, 12 min after beginning of ischemia rabbits were randomized to intravenous infusion of 30 mg coenzyme Q10 (Eisai Co., Japan) (n = 10) or vehicle (n = 10). In Protocol 2, rabbits were randomized to 30 mg coenzyme Q10 (n = 6) or vehicle (n = 6) treatment 60 min before ischemia. Ischemic zone at risk (IZ) was assessed by blue dye and necrotic zone (NZ) by tetrazolium staining. RESULTS: In both protocols, coenzyme Q10 did not alter heart rate, mean blood pressure, or regional myocardial blood flows in either the ischemic or non-ischemic zones during ischemia or reperfusion. No difference was found in IZ (as fraction of LV weight) (Protocol 1: 0.24 +/- 0.02 vs. 0.25 +/- 0.02; Protocol 2: 0.28 +/- 0.02 vs. 0.28 +/- 0.03, in the control vs. coenzyme Q10 groups, respectively). The NZ/IZ ratio was comparable between the groups in both protocols (Protocol 1: 0.22 +/- 0.04 vs. 0.26 +/- 0.04; Protocol 2: 0.21 +/- 0.06 vs. 0.30 +/- 0.06, in the control vs. coenzyme Q10 groups, respectively). CONCLUSIONS: Coenzyme Q10, administered acutely either during or 60 min before myocardial ischemia, does not attenuate infarct size in the rabbit.

An adenosine A1 receptor agonist, R(-)-N-(2-phenylisopropyl)-adenosine (PIA), but not adenosine itself, acts as a therapeutic preconditioning-mimetic agent in rabbits.

OBJECTIVE: A preconditioning mimetic agent could be useful therapy for cardiac ischaemic events; stimulation of adenosine receptors has been proposed as a preconditioning mediator. The ability of adenosine-receptor activation to mimic ischaemic preconditioning was tested in an in vivo rabbit model. METHODS: Adenosine (15 mg, a maximally tolerated dose, n = 10) was infused over six minutes via a coronary artery and compared with saline (n = 12) in anaesthetised rabbits. Five minutes after infusion, a coronary artery was occluded for 40 minutes followed by three hours of reperfusion. In a second study, preischaemic intravenous treatment with adenosine (25 mg.kg-1, n = 9), or an A1-adenosine agonist, R(-)-N-(2-phenylisopropyl)-adenosine (PIA, 900 micrograms.kg-1, n = 12), were compared with saline (n = 12), when given before 40 minutes of coronary artery ligation and three hours of reperfusion in anaesthetised rabbits. RESULTS: Intracoronary adenosine reduced mean arterial pressure during infusion (48(3) v 80(4) mm Hg, control, p < 0.001); however, infusion regional myocardial blood flow was significantly higher in adenosine treated hearts (5.00(0.90) v 2.30(0.26) ml.min-1 x g-1, p < 0.02) in the region later to become ischaemic. During occlusion ischaemic blood flow was similar in both groups as was the size of the ischaemic risk region, expressed as a % of the left ventricle (42(3)% adenosine and 37(3)% control, NS). Intracoronary adenosine treatment failed to reduce infarct size (52(5)% of the risk zone v 57(7)% in controls, NS). In the second protocol, heart rate immediately after treatment was reduced by both intravenous denosine (26%) and PIA (22%) v control, indicating atrial A1 receptor activation. Treatment with PIA resulted in a significant reduction in ultimate infarct size compared with saline (38(5)% of risk region v 57(5)%, p < 0.05). Adenosine, however, failed to reduce infarct size (50(8)%, NS v saline). There were no differences between area at risk or myocardial blood flow among groups. CONCLUSION: The adenosine agonist PIA but not adenosine itself might be a useful adjunctive therapy.

Direct evidence that ischemic preconditioning does not cause protein kinase C translocation in rabbit heart.

OBJECTIVE: Indirect pharmacological evidence suggests that myocardial protection conferred by ischemic preconditioning in rabbit myocardium is mediated through the translocation of protein kinase C (PKC). To test this hypothesis, we performed direct biochemical measurements of subcellular distribution of PKC in rabbit hearts. METHODS: Two protocols were utilized. In Protocol I the preconditioned group (PC) underwent two 5-min episodes of brief coronary artery occlusion each followed by 5 min of reperfusion, while the control group consisted of time-matched, sham-operated (non-ischemic) animals (SO). Tissue samples were homogenized and cytosolic and particulate fractions were obtained by ultracentrifugation. In Protocol II one group of rabbits received ischemic preconditioning as in Protocol I followed by 10 min of sustained ischemia (PC + IS); a second control group was subjected to 10 min of sustained ischemia (IS); and the third group was time-matched, sham-operated (non-ischemic) animals (SO). Homogenized tissue samples were separated into cytosolic, nuclear and membrane fractions. RESULTS: In Protocol I, no differences in the subcellular distribution of PKC between the SO and PC groups were observed. In Protocol II, when samples were obtained at 10 min of sustained ischemia, no changes in the subcellular distribution of PKC were observed between SO, IS and PC + IS groups. CONCLUSION: Our results indicate that translocation of protein kinase C is not an important mediator of ischemic preconditioning in the rabbit ischemia model.

Correlates of reperfusion ventricular fibrillation in dogs.

To elucidate determinants of reperfusion ventricular fibrillation (VF), regional myocardial blood flow, ATP, creatine phosphate (CP), heart rate and blood pressure were compared in 2 groups of anesthetized dogs: those that fibrillated spontaneously upon release of a 15-minute coronary artery occlusion (VF group, n = 8) and those that did not fibrillate when reperfused (No VF group, n = 27). Arterial pressure and heart rate before and during coronary artery occlusion were similar in both groups. Ischemic endo- and epicardial ATP values, measured at the end of the occlusion period, were reduced approximately 20% of nonischemic values in both groups. In contrast, CP (nmol . mg protein-1) within the ischemic zone was significantly lower in the VF group in both the epicardium (14.3 +/- 1.6 in the VF group vs 22.8 +/- 2.5 in the No VF group, p less than 0.01) and the endocardium (9.0 +/- 2.0 in the VF group vs 18.7 +/- 1.8 in the No VF group, p less than 0.01). Furthermore, epi- and endocardial regional myocardial blood flow in the center of the ischemic zone during occlusion was significantly lower in VF dogs than in No VF dogs. Epicardial flow was 0.06 +/- 0.03 ml X min-1 X g-1 in VF dogs vs 0.44 +/- 0.06 in No VF dogs (p less than 0.001) and endocardial flow was 0.03 +/- 0.02 ml X min-1 X g-1 in VF dogs vs 0.23 +/- 0.04 ml X min-1 X g-1 in No VF dogs (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Is warm retrograde blood cardioplegia better than cold for myocardial protection?

BACKGROUND: This study tests the hypothesis that continuous normothermic retrograde blood cardioplegia is superior to cold intermittent blood cardioplegia in protecting the left and right side of the heart transmurally during an extended cross-clamping period. METHODS: Twelve anesthetized, open chest dogs were placed on cardiopulmonary bypass and randomized to receive continuous warm (n = 6) or intermittent cold cardioprotection (n = 6) during a 3-hour aortic cross-clamp period. Transmural left ventricular muscle biopsy specimens were taken before the initiation of cardiopulmonary bypass and 90 and 180 minutes after cross-clamping. Right ventricular (RV) biopsy specimens were taken 180 minutes after aortic cross-clamping. Biopsy specimens were analyzed for adenosine triphosphate, creatine phosphate, and lactate levels and for morphologic changes via electron microscopy. RESULTS: At the end of 180 minutes of cardiopulmonary bypass, the adenosine triphosphate contents of endocardial and epicardial halves of the left ventricular myocardium were only slightly degraded in both cardioplegia groups; a significantly greater reduction in adenosine triphosphate levels occurred in the RV of the warm compared with the cold group (p < 0.02). The difference in creatine phosphate values in the left ventricle between the cold group (35.2 +/- 23.4 nmol/mg cardiac protein) and the warm animals (64.4 +/- 24.9 nmol/mg cardiac protein) was not statistically significant, but the RV creatine phosphate stores were significantly better preserved in the warm compared with the cold cardioplegia group (p < 0.02). Lactate levels increased to a similar extent in both groups, but both values rose significantly over baseline (p < 0.03). Importantly the electron microscopic score of the left ventricle and RV indicated that cells were reversibly and not irreversibly damaged with both cardioplegic protections. CONCLUSIONS: These results suggest the following: (1) Chemical arrest is a major contributor of myocardial preservation during diastolic arrest as used in clinical cardiac surgery. (2) Both methods preserve the ultrastructure of the myocytes transmurally during 3 hours of aortic cross-clamping. (3) Both techniques protect the RV and left ventricle; however, to provide optimal protection of the RV, alternated retrograde and antegrade perfusion might be beneficial over retrograde cardioplegia flow alone, in particular with warm cardioplegia.

Echocardiographic and cardiac Doppler assessment of mice.

Recent studies have suggested that intermediate-frequency M-Mode transthoracic echocardiographic imaging is a promising method for evaluating the left ventricle in transgenic mice. However, there is a paucity of data regarding two-dimensional (2-D) echocardiography and cardiac Doppler echocardiography in this model. Therefore we studied 15 mice (body weights 38 to 65 gm) with an ultrasound system equipped with a 9 MHz transducer. M-mode, 2-D, pulsed, and color-flow Doppler studies were performed. Mean +/- SD for septal, posterior wall, and left ventricular cavity dimensions at end diastole were the following: M-mode: 1.1 +/- 0.2, 1.0 +/- 0.2, and 3.7 +/- 0.7 mm; 2-D: 1.0 +/- 0.2, 1.1 +/- 0.3, and 3.0 +/- 0.6mm. Left ventricular fractional shortening was assessed from the M-mode echocardiogram: mean 53.7% +/- 10.7% (range 42% to 77%). 2-D assessment of left ventricular mass correlated better with left ventricular mass identified at necropsy than left ventricular mass identified by M-mode echocardiography (r = 0.70; p = 0.007 versus r = 0.07; p not significant). 2-D visualization of left ventricle, proximal aorta, and aortic and mitral valves was excellent and was obtained mainly from a "parasternal" window. Apical views were more difficult to obtain. Mean +/- SD for aortic peak and mean velocities and velocity-time integral were 0.53 +/- 0.13, 0.32 +/- 0.08, and 0.025 +/- 0.008 m/sec. Estimated stroke volume was 0.0506 +/- 0.018 ml/beat. Cardiac output was 12.64 +/- 7.87 ml/min. Mean +/- SD for mitral peak E, peak A, and E/A ratio were 0.45 +/- 0.09 m/sec, 0.19 +/- 0.06 m/sec, and 2.4 +/- 0.66 m/sec, respectively. In all mice the E/A ratio was greater than 1 (range 1.76 to 3.6). Color-flowing imaging clearly displayed normal mitral inflow and left ventricular outflow. In one mouse, aortic regurgitation was recorded by pulsed Doppler echocardiography. Echocardiographic, pulsed, and color-flow Doppler assessment of mice is feasible. In this study left ventricular mass was assessed better by 2-D measurement of left ventricular dimensions. Assessment of left ventricular performance is feasible. Color Doppler-guided evaluation of aortic flow and aortic root measurement permits assessment of stroke volume and cardiac output.

Protection of myocardium by transient, preischemic administration of phenylephrine in the rabbit.

BACKGROUND: Transient ischemia protects the myocardium from subsequent, more prolonged ischemic episodes; however, other forms of stress before ischemia might also provide a preconditioning effect. Our objective was to test the hypothesis that phenylephrine, an alpha-adrenergic agonist, given before ischemia can act as a pharmacologic preconditioning agent and protect the myocardium. METHODS: Phenylephrine, 50 micrograms/kg, was given as a bolus 15 min before coronary artery occlusion in 11 anesthetized open-chest rabbits; 12 control rabbits received saline. All rabbits underwent 30 min coronary artery occlusion and 4 h reperfusion. Regional myocardial blood flow was quantified using radioactive microspheres, infarct size by tetrazolium staining, and risk zone by blue dye. RESULTS: Pretreatment with phenylephrine significantly reduced necrosis. Infarcted myocardium comprised 23 +/- 4% of the region at risk in treated rabbits compared with 39 +/- 4% in control animals (P < 0.01). Mean systolic arterial pressure increased briefly after administration of phenylephrine (98 +/- 5 to 141 +/- 7 mmHg) but returned to baseline before occlusion. Heart rate was similar in both groups at baseline but decreased slightly with phenylephrine treatment. Regional myocardial blood flow increased after injection of the phenylephrine bolus to 2.86 +/- 0.22 compared with 2.25 +/- 0.08 ml/min/g in control animals (P = 0.02), but both groups were equally ischemic during occlusion. CONCLUSION: Transient, preischemic treatment with phenylephrine makes the myocardium more resistant to necrosis during ensuing ischemia and reperfusion.

Ischemic preconditioning and long-chain acyl carnitine in the canine heart.

BACKGROUND: This study investigated the effects of ischemic preconditioning on myocardial carnitine-linked metabolism and high-energy phosphates in the canine model of ischemia and reperfusion. METHODS: Anesthetized dogs underwent 1 hour of coronary artery occlusion and 4.5 hours of reperfusion. The dogs were randomly assigned to a control group (no intervention for 30 minutes), a preconditioned group (four repeated episodes of 3 minutes of mechanical coronary occlusion, each followed by 5 minutes of reperfusion), and a coronary cyclic flow variation (CFV) group (coronary artery stenosis and endothelial injury, resulting in an average of four episodes of platelet thrombosis and dislodgment). After completion of the protocol, ATP, creatine phosphate, and long-chain acyl carnitine concentrations were studied in both nonischemic and previously ischemic myocardium. RESULTS: In Part I of this study (Ovize et al., Circulation 1992, 85:779-789), it was reported that both mechanical occlusion and CFV before sustained occlusion resulted in a decrease in infarct size. In the present paper, we report changes in high-energy phosphates and long-chain acyl carnitine in these groups. Control, preconditioned, and CFV groups showed similar depletion in ATP content and "overshoot" in creatine phosphate stores. Control dogs exhibited a significant accumulation of long-chain acyl carnitine in the previously ischemic tissue (219 +/- 61 vs 131 +/- 38 nmoles/g wet weight in the nonischemic tissue; P < 0.05). No significant increase in long-chain acyl carnitine occurred in the mechanically preconditioned and CFV groups. CONCLUSIONS: These results indicate that brief episodes of transient ischemia before sustained coronary occlusion prevent long-chain acyl carnitine accumulation in the ischemic and reperfused canine myocardium.

Intraluminal bypass device for arterial surgery.

Over 50,000 artificial grafts are implanted every year in the United States. Present surgical procedures require either bypass or clamping off of the vessel to be replaced. Complications of these techniques include aneurysms and left ventricular overload. In addition, for aortic procedures paraplegia or even death can occur. A simple surgical procedure that does not require cardiopulmonary bypass, external shunts, or cross-clamping was developed and tested in dogs. An intraluminal bypass device was developed to allow blood to flow through the aorta to the lower limbs during the procedure. Blood flow stoppage was minimized, which should lead to a reduction of morbidity and mortality.

Effects of resveratrol, a flavinoid found in red wine, on infarct size in an experimental model of ischemia/reperfusion.

OBJECTIVE: Resveratrol is a potent anti-inflammatory and anti-oxidant flavinoid found in red wine. Resveratrol has been shown to improve ventricular function and decrease lactic dehydrogenase release after ischemia in rats. The aim of this study was to test whether resveratrol could provide direct cardioprotection to myocytes during acute myocardial infarction. METHOD: Anesthetized, open-chest rabbits (N= 24) were subjected to 30 minute coronary artery occlusion followed by 3 hr reperfusion. Before the onset of ischemia (15 minutes), the rabbits were randomly assigned (n = 8 in each group) to either high-dose (1.5 mg/kg) resveratrol, low-dose (0.15 mg/kg) resveratrol or ethanol vehicle, and the effects on infarct size and regional myocardial blood flow (RMBF) were tested. RESULTS: Hemodynamic parameters and size of ischemic risk region (29% to 35% of the left ventricle) were similar in all groups. Infarct size, expressed as a mean (SEM) percentage of the risk region, was 46% (5%) of the risk region in controls, 46% (7%) in the low-dose group and 54% (3%) in the high-dose group (p = .53). Thus, treatment with resveratrol had no effect on infarct size at either dose. There were no differences in RMBF in the risk zone or in nonischemic tissue, during either occlusion or reperfusion. CONCLUSIONS: In this intact model of ischemia and reperfusion, resveratrol fails to provide cardioprotection. The mechanism of other beneficial effects (e.g., improvement of function) that are observed with resveratrol probably do not result from increased RMBF or a reduction in myocardial necrosis.

Incidence of diabetic retinopathy in people with type 2 diabetes mellitus attending the Diabetic Retinopathy Screening Service for Wales: retrospective analysis.

OBJECTIVES: To determine the incidence of any and referable diabetic retinopathy in people with type 2 diabetes mellitus attending an annual screening service for retinopathy and whose first screening episode indicated no evidence of retinopathy. DESIGN: Retrospective four year analysis. SETTING: Screenings at the community based Diabetic Retinopathy Screening Service for Wales, United Kingdom. PARTICIPANTS: 57,199 people with type 2 diabetes mellitus, who were diagnosed at age 30 years or older and who had no evidence of diabetic retinopathy at their first screening event between 2005 and 2009. 49,763 (87%) had at least one further screening event within the study period and were included in the analysis. MAIN OUTCOME MEASURES: Annual incidence and cumulative incidence after four years of any and referable diabetic retinopathy. Relations between available putative risk factors and the onset and progression of retinopathy. RESULTS: Cumulative incidence of any and referable retinopathy at four years was 360.27 and 11.64 per 1000 people, respectively. From the first to fourth year, the annual incidence of any retinopathy fell from 124.94 to 66.59 per 1000 people, compared with referable retinopathy, which increased slightly from 2.02 to 3.54 per 1000 people. Incidence of referable retinopathy was independently associated with known duration of diabetes, age at diagnosis, and use of insulin treatment. For participants needing insulin treatment with a duration of diabetes of 10 years or more, cumulative incidence of referable retinopathy at one and four years was 9.61 and 30.99 per 1000 people, respectively. CONCLUSIONS: Our analysis supports the extension of the screening interval for people with type 2 diabetes mellitus beyond the currently recommended 12 months, with the possible exception of those with diabetes duration of 10 years or more and on insulin treatment.

Ethanol does not exert myocardial preconditioning in an intact rabbit model of ischemia/reperfusion.

Some epidemiologic analyses suggest that moderate drinking of alcohol may have beneficial effects on the heart. An experimental in vitro study also indicated that acute alcohol administration may precondition myocardium against ischemia, but only if it is washed out before ischemia. The goal of this study was to test whether alcohol + washout preconditions the myocardium to ischemia, reducing necrosis after ischemia/reperfusion in an in vivo model. Two groups of anesthetized open-chest rabbits received ethanol (0.5 mL/kg, intravenously) at 90 minutes before (Group 1, alcohol preconditioning, n = 8) or 5 minutes before (Group 2, acute, n = 8) coronary artery occlusion (CAO); control rabbits received saline (Group 3, n = 8). All rabbits received 30 minutes of CAO and 3 hours of reperfusion. Blood alcohol level at the time of CAO in Group 1 had returned to control level (< 10 mg/dL). Alcohol level in Group 2 was 162 +/- 9 mg/dL. There were no differences in hemodynamics, ischemic risk region size, or collateral blood flow among groups. Alcohol, with or without washout, failed to reduce necrosis. Infarct size (% risk region) was 45 +/- 5% in control rabbits, 48 +/- 6% with acute administration, and 53 +/- 7% with washout (P = 0.57). These data indicate that alcohol + washout did not precondition hearts against ischemia in this model, adding evidence to the theory that acute alcohol administration has no direct beneficial effect on ischemic myocardium.

Combination therapy for maximal myocardial infarct size reduction.

The aim of this study was to test whether myocardial infarct size reduction would be optimized by combining three known effective therapies: cariporide, regional hypothermia, and ischemic preconditioning (CHIP). Before coronary artery occlusion (CAO), treated rabbits (CHIP, n = 7) received cariporide (0.3 mg/kg), ischemic preconditioning (7 minutes ischemia and 5 minutes reperfusion), then 20 minutes of mild regional hypothermia (34 degrees C). Control rabbits (n = 7) received saline and a 34-minute waiting period. All received 30 minutes of CAO and reperfusion. In another study, rabbits (n = 8 in each group) received 90 minutes of CAO. In the 30-minute protocol, the authors found that hearts in both groups were equally ischemic during CAO. Mean ischemic risk zones were similar in both groups; however, in CHIP hearts, infarct size was 4 +/- 1% of risk zone, a reduction of 91% compared with control rabbits (44 +/- 7% of the risk zone, P = 0.001). In the 90-minute protocol, risk zone size was similar in both groups, but infarct size in control hearts was 76 +/- 3% of the risk zone compared with 34 +/- 7% in CHIP treated hearts (P = 0.0003). In summary, the combined treatment provided extraordinary protection. Infarct comprised only 4% of the risk region after 30-minute ischemia-a far greater reduction than was previously observed in the same laboratory using any single intervention. After 90 minutes of ischemia, infarct was 55% lower in CHIP hearts, suggesting that this therapeutic approach dramatically reduces ischemia/reperfusion cell death, even during long occlusions.