Myocardial function and coronary blood flow response to acute ischemia in chronic canine diabetes

The Contribution of Cardiac Fatty Acid Oxidation to Diabetic Cardiomyopathy Severity

Diabetes is a major risk factor for the development of cardiovascular disease via contributing and/or triggering significant cellular signaling and metabolic and structural alterations at the level of the heart and the whole body. The main cause of mortality and morbidity in diabetic patients is cardiovascular disease including diabetic cardiomyopathy. Therefore, understanding how diabetes increases the incidence of diabetic cardiomyopathy and how it mediates the major perturbations in cell signaling and energy metabolism should help in the development of therapeutics to prevent these perturbations. One of the significant metabolic alterations in diabetes is a marked increase in cardiac fatty acid oxidation rates and the domination of fatty acids as the major energy source in the heart. This increased reliance of the heart on fatty acids in the diabetic has a negative impact on cardiac function and structure through a number of mechanisms. It also has a detrimental effect on cardiac efficiency and worsens the energy status in diabetes, mainly through inhibiting cardiac glucose oxidation. Furthermore, accelerated cardiac fatty acid oxidation rates in diabetes also make the heart more vulnerable to ischemic injury. In this review, we discuss how cardiac energy metabolism is altered in diabetic cardiomyopathy and the impact of cardiac insulin resistance on the contribution of glucose and fatty acid to overall cardiac ATP production and cardiac efficiency. Furthermore, how diabetes influences the susceptibility of the myocardium to ischemia/reperfusion injury and the role of the changes in glucose and fatty acid oxidation in mediating these effects are also discussed.

The pulmonary artery catheter in 2008 - A (finally) maturing modality?

The first description of the flow-directed pulmonary artery catheter (PAC) was published in the 1970s by Jeremy Swan and William Ganz. Ever since its clinical debut, many controversies surrounded the use of the PAC. Regardless of these controversies, the most fundamental issues surrounding this hemodynamic monitoring device remain unresolved, including the exact indications, contraindications, identification of patients who potentially benefit from this technology, and the way we interpret and use PAC-derived parameters. Despite recent intensification of attacks against the use of the PAC by its opponents, it seems overly harsh to discount a technology that might be beneficial in appropriately selected clinical situations, especially when considering the fact that our true knowledge of this technology is somewhat limited. In fact, the PAC may still play an important role considering the resurgence of the concepts of euvolemic resuscitation and hemodynamic sufficiency.

Republished with Permission from: Stawicki SP, Prosciak MP. The pulmonary artery catheter in 2008 – a (finally) maturing modality? OPUS 12 Scientist 2008;2(4):5-9.

Echocardiographic assessment of coronary artery flow in normal canines and model dogs with myocardial infarction

This study was conducted to evaluate the usefulness of coronary arterial profiles from normal dogs (11 animals) and canines (six dogs) with experimental myocardial infarction (MI) induced by ligation of the left coronary artery (LCA). Blood velocity of the LCA and right coronary artery (RCA) were evaluated following transthoracic pulsed-wave Doppler echocardiography. The LCA was observed as an infundibular shape, located adjacent to the sinus of Valsalva. The RCA appeared as a tubular structure located 12 o'clock relative to the aorta. In normal dogs, the LCA and RCA mean peak diastolic velocities were 20.84 ± 3.24 and 19.47 ± 2.67 cm/sec, respectively. The LCA and RCA mean diastolic deceleration times were 0.91 ± 0.14 sec and 1.13 ± 0.20 sec, respectively. In dogs with MI, the LCA had significantly (p < 0.01) lower peak velocities (14.82 ± 1.61 cm/sec) than the RCA (31.61 ± 2.34 cm/sec). The RCA had a significantly (p < 0.01) rapid diastolic deceleration time (0.71 ± 0.06 sec) than that found in the LCA (1.02 ± 0.22 sec) of MI dogs. In conclusion, these profiles may serve as a differential factor for evaluating cardiomyopathy in dogs.

Isolation and characterization of mitochondria from goat hearts

Cardiac mitochondria provide energy for the contraction/relaxation cycle. The aim of our study was to isolate and characterize mitochondria from Caprine hearts under control and in-vitro induced ischemia. A decrease in activities of all the enzymes was observed in the ischemic models. Further characterization of proteins was done by SDS-PAGE and BN-PAGE. Lipids have been characterized by analyzing the phospholipids by HPTLC and fatty acids by GLC in both groups. Our results indicated that injury occurs early in the course of ischemia and progresses during ischemia. TBARS and carbonyl content have also been measured. The in-vitro effects of fatty acids have been studied on the enzymes and complexes of mitochondria.

The effect of diabetes and poor left ventricular function on bone marrow cell-induced myocardial protection

OBJECTIVES

The myocardium of patients with diabetes and poor left ventricular (LV) function cannot be protected by interventions such as ischemic preconditioning (IP). We investigated whether these clinical conditions influence the protection elicited by the paracrine effect of bone marrow cells (BMCs) and whether the cause for loss in protection resides in the BMCs, the myocardium, or both.

METHODS

BMCs and right atrial appendage were obtained from patients with and without diabetes and from poor (EF < 30%) and preserved LV function undergoing elective cardiac surgery. Muscles (n = 6/group) were co-cultured with BMCs and subjected to 90 min ischemia/120 min reoxygenation at 37°C. The degree of protection was assessed by measuring creatine kinase (CK) released, and myocardial cell necrosis and apoptosis.

RESULTS

Ischemia-induced CK release, cell necrosis, and apoptosis in the diabetic myocardium were not significantly affected by IP or by co-incubation with autologous or non-diabetic allogenic BMCs. Conversely, significant reduction in CK release, cell necrosis, and apoptosis were observed when non-diabetic myocardium was co-incubated with allogenic diabetic BMCs. Interestingly, while allogenic BMCs from subjects with preserved LV function exerted a modest but significant reduction in CK leakage and cell necrosis, but not apoptosis, on failing myocardium, the BMCs from patients with poor LV function failed to protect their own and the allogenic myocardium from subjects with normal LV function.

CONCLUSIONS

The failure to protect the myocardium of patients with poor LV function against ischemia/reoxygenation-induced injury is mainly due to a deficit in their BMCs and the myocardium itself, whereas in patients with diabetes the deficit remains within the myocardium and not in the BMCs.

Effects of epinephrine on underperfusion-reperfusion injuries in diabetic and non-diabetic rat hearts

The sympathetic nervous systems may bear relevance to the increased incidence of heart failure in diabetes (DM). In our isolated rat hearts perfused at constant low flow rate, norepinephrine dose-dependently enhanced diabetic myocardial damage, particularly during underperfusion. The purpose of this investigation is to examine the effects of epinephrine on the ischemic injury and on the reperfusion injury in DM and non-DM rat hearts, and to clarify whether the cardiac states during underperfusion at constant low pressure are similar to those at constant low flow rate. Isolated streptozotocin-induced 6-week DM and non-DM rat hearts with a balloon in the left ventricle (LV) were paced and normal perfused at 75 cm H2O with normoxic Krebs-Henseleit solution. Then the hearts were underperfused at 35 cm H2O, a constant low pressure with below one-third of the pre-ischemic coronary perfusion flow (CPF) level. Four min after the start of underperfusion, the perfusate was changed to that containing epinephrine 10(-6) M. After 45 min underperfusion with or without epinephrine, all of the hearts were reperfused without epinephrine at 75 cm H2O for 45 min. To detect changes in LV stiffness, the isometric tension along the longitudinal direction of the whole heart and the LV isovolumic pressure were monitored simultaneously. In DM hearts, the underperfusion alone caused a slight increase in LV stiffness, and all the changes recovered to the pre-ischemic levels during reperfusion. Epinephrine during underperfusion accelerated the start of increase in LV stiffness and the decrease in CPF. During reperfusion the changes recovered partly to the control levels. In non-DM hearts, epinephrine during underperfusion caused only a slight increase in LV stiffness though a similar low CPF to DM hearts. However, the reperfusion caused a marked increase in LV stiffness and a lower recovery of CPF. Epinephrine at constant low pressure, as well as norepinephrine at constant low flow rate, enhanced the ischemic injury, particularly in DM hearts, while aggravated the reperfusion injury in non-DM hearts.

Metabolic abnormalities in the diabetic heart

Congestive heart failure is a major health problem in the diabetic. Diabetics have a high incidence of heart disease, including an increased incidence and severity of congestive heart failure than the non-diabetic. Progression to heart failure after an acute myocardial infarction is also more frequent in diabetics then non-diabetics. While atherosclerosis and ischemic injury are important contributing factors to this high in incidence of heart failure, another important factor is diabetes-induced changes within the heart itself. A prominent change that occurs in the diabetic is a switch in cardiac energy metabolism. Increases in fatty acid oxidation accompanied by decreases in glucose metabolism can result in the myocardium becoming almost entirely reliant on fatty acid oxidation as a source of energy. This switch in energy metabolism contributes to congestive heart failure by increasing the severity of injury following an acute myocardial infarction, and by having direct negative effects on contractile function. This paper will review the evidence linking alterations in energy metabolism to alterations in contractile function in the diabetic.

Treatment of heart failure in patients with diabetes mellitus

Patients with diabetes mellitus have an increased morbidity and mortality from cardiovascular disease. Both coronary artery disease and congestive heart failure (CHF) are largely responsible for the increased cardiovascular adverse events in patients with diabetes. This review discusses the pathophysiology of CHF, the mechanisms of left ventricular (LV) dysfunction and the neurohormonal mechanisms involved in both LV dysfunction and CHF. Diabetes with and without hypertension is an important cause of LV dysfunction and CHF. Diabetes may be responsible for the metabolic and ultrastructural causes of LV dysfunction, while hypertension may be responsible for the marked fibrotic changes that are found. Experimental induction of diabetes in animals has shed light on the biochemical and ultrastructural changes seen. The role of insulin to reverse both metabolic and structural changes is reviewed both from experimental data and with the limited amount of clinical data available. The therapy of CHF in patients with diabetes is similar to that of patients without diabetes, with therapy directed toward the use of beta-blockers and angiotensin converting enzyme (ACE) inhibitors. As the morbidity and mortality are higher in patients with diabetes, several studies have pointed out the importance of this subgroup where the opportunity to make a significant clinical impact exists. A significant opportunity exists to reduce morbidity and mortality with beta-blockers and ACE inhibitors when ischaemia and CHF are both present. However, studies in patients diabetes have been limited to post hoc subgroup analyses and rarely as predefined subgroups. Clinical trials involving patients with diabetes with and without hypertension and LV dysfunction are clearly needed in the future to adequately address the needs of this high risk subgroup.

A comparison of ultrastructural changes on endomyocardial biopsy specimens obtained from patients with diabetes mellitus with and without hypertension

The pathogenesis of diabetic cardiomyopathy is unknown. The synergistic, or enhanced, effect of hypertension on pathological changes in the heart of diabetic patients has been highly suspected. The purpose of this study was to evaluate the myocardial changes related to diabetes mellitus with and without hypertension, using biopsy specimens. We examined the ultrastructural changes in biopsy specimens of the endomyocardium obtained from 25 patients. They were divided into four groups: controls without hypertension or diabetes mellitus (n = 6), and patient with hypertension (n = 3), diabetes mellitus (n = 8), and diabetes with hypertension (n = 8). The diabetic patients showed nearly normal or mildly depressed systolic left ventricular function. Ultrastructural pictures were analyzed for thickening of the capillary basement membrane, presence of toluidine blue-positive materials (i.e., materials showing metachromasia) in the myocytes, size of myocytes, and interstitial fibrosis. The thickening of the capillary basement membrane, the accumulation of toluidine blue-positive materials, and interstitial fibrosis were all significantly greater in the patients with diabetes mellitus compared to the control subjects. The myocytes tended to be small (cell atrophy) in the diabetes group. Although these pathological changes in the heart were characteristic of diabetic patients, irrespective of the presence or absence of hypertension, the presence of hypertension increased the pathological changes of myocardial cells as well as abnormality in the capillary vessels in patients with diabetes mellitus. Alterations in the myocardial cells and capillaries, caused by diabetes mellitus, may lead to myocardial cell injury and interstitial fibrosis and, ultimately, to ventricular systolic and diastolic dysfunction, especially when the diabetes is accompanied by hypertension.

Cardiac consequences of diabetes mellitus

A variety of disciplines including noninvasive and invasive cardiac methodologies, as well as epidemiologic studies, have provided information that has altered our view on the relation of diabetes to cardiac disease. Instead of an exclusive focus on coronary artery disease, it is now recognized that heart muscle can be independently involved in diabetic patients. In diabetics without known cardiac disease, abnormalities of left ventricular mechanical function have been demonstrated in 40 to 50% of subjects, and it is primarily a diastolic phenomenon. Left ventricular hypertrophy may eventually appear in the absence of hypertension. The diastolic dysfunction appears related to interstitial collagen deposition, largely attributable to diminished degradation. The presence of even moderate obesity intensifies the abnormality. Reversibility of this process is not readily achieved with chronic insulin therapy. Experimental studies have indicated normalization of the collagen alteration by endurance training, begun relatively early in the disease process. General measures of management include the control of other cardiac risk factors and a reasonable program of physical activity. The high mortality during an initial acute myocardial infarction has been attributed to heart failure, which is managed as in nondiabetic patients. Recently, the early introduction of aspirin, thrombolysis, and beta-adrenergic blockade has reduced mortality during the initial infarction. Chronic use of the latter agent over the subsequent years has also proven to be more beneficial in diabetic patients with acute myocardial infarction compared with nondiabetic patients.

Glycolysis and glucose oxidation during reperfusion of ischemic hearts from diabetic rats

Stimulation of glucose oxidation by dichloroacetate (DCA) treatment is beneficial during recovery of ischemic hearts from non-diabetic rats. We therefore determined whether DCA treatment of diabetic rat hearts (in which glucose use is extremely low), increases recovery of function of hearts reperfused following ischemia. Isolated working hearts from 6 week streptozotocin-diabetic rats were perfused with 11 mM [2-3H/U-14C]glucose, 1.2 mM palmitate, 20 microU/ml insulin, and subjected to 30 min of no flow ischemia followed by 60 min reperfusion. Heart function (expressed as the product of heart rate and peak systolic pressure), prior to ischemia, was depressed in diabetic hearts compared to controls (HR x PSP x 10(-3) was 18.2 +/- 1 and 24.3 +/- 1 beats/mm Hg/min in diabetic and control hearts respectively) but recovered to pre-ischemic levels following ischemia, whereas recovery of control hearts was significantly decreased (17.8 +/- 1 and 11.9 +/- 3 beats/mm Hg/min in diabetic and control hearts respectively). This enhanced recovery of diabetic rat hearts occurred even though glucose oxidation during reperfusion was significantly reduced as compared to controls (39 +/- 6 and 208 +/- 42 nmol/min/g dry wt, in diabetic and control hearts respectively). Glycolytic rates (3H2O production) during reperfusion were similar in diabetic and control hearts (1623 +/- 359 and 2071 +/- 288 nmol/min/g dry wt, respectively). If DCA (1 mM) was added at reperfusion, hearts from control animals exhibited a significant improvement in function (HR x PSP x 10(-3) recovered to 20 +/- 4 beats/mm Hg/min) that was accompanied by a 4-fold increase in glucose oxidation (from 208 +/- 42 to 753 +/- 111 nmol/min/g dry wt). DCA was without effect on functional recovery of diabetic rat hearts during reperfusion but did significantly increase glucose oxidation from 39 +/- 6 to 179 +/- 44 nmol/min/g dry wt). These data suggest that, unlike control hearts, low glucose oxidation rates are not an important factor in reperfusion recovery of previously ischemic diabetic rat hearts.

Early intervention of inotropic support in facilitating weaning from cardiopulmonary bypass: the New England Deaconess Hospital experience

The current article reviews the therapeutic advantages and disadvantages of early inotropic intervention prior to separation from cardiopulmonary bypass (CPB). Background information is provided on predictors of failure to wean as well as the multiple etiologies and consequences of the "failed wean" from CPB. Advantages of early inotropic intervention include (1) increased contractility, (2) resolution/prevention of ischemia, (3) attainment of therapeutic levels of drug, (4) minimization of inotropic side effects while on CPB, (5) avoidance of mechanical intervention (intra-aortic balloon pump), (6) dilatation of the internal mammary artery, and (7) prevention of the "failed wean". Disadvantages of early inotropic intervention include (1) unnecessary drug usage, (2) tachycardia/arrhythmias, (3) hyper/hypotension, (4) metabolic disturbances (hyperglycemia), (5) coagulation disorders, (6) need for additional drugs to treat side effects, (7) possible myocardial damage, and (8) additional costs. A brief review of this institution's preference for amrinone follows, including its pharmacology, side effects, and dosing prior to separation from CPB. Due to the large percentage of patients with diabetes mellitus undergoing cardiac surgery at our institution (approximately 30% to 40%) a synopsis of special inotropic considerations for this patient population is included.

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.

Coronary blood flow in chronic insulin-dependent diabetic dogs

Diabetic patients appear to be at an increased risk for perioperative morbidity and mortality following coronary artery bypass grafting. Many have suggested that microangiopathy is a primary cause. Using radionuclide labelled microspheres, we measured the perfusion of the subendocardium, midmyocardium, subepicardium, and the subendocardium/subepicardium ratio in alloxan-induced diabetic and normal dogs. We found no statistical difference in the myocardial perfusion of dogs made diabetic for five months when compared to normal dogs. By using repeated measures two-factor analysis of variance-regression model, changing blood glucose levels had no effect on coronary blood flow in either the diabetic or normal dogs.

Vectorcardiographic evaluation of diabetic cardiomyopathy and of its contributing factors

In order to investigate the prevalence of vectorcardiographic bites, expression of small areas of fibrosis, atrophy or degeneration of the myocardium, we studied, using the vectorcardiograms (VCG) of 101 diabetic patients (35 with insulin-dependent and 66 with non-insulin-dependent diabetes mellitus, aged from 25 to 60 years, without hypertension, coronary artery disease, or intraventricular conduction defects) and 228 normal control subjects, matched for age and sex. The prevalence of bites was 38.6% in diabetic patients and 10.0% in the control group (p less than 0.001). Diabetic patients were also subdivided into groups according to age, sex, metabolic control, risk factors for coronary heart disease, type of diabetes, duration of diabetes and diabetic microangiopathy. No correlation was found between any of the variables investigated nor of a combination of these, and the presence of bites. We conclude that VCG is a sensitive test for cardiac involvement in diabetic patients but that it cannot be used to identify any specific factor able to influence the onset and evolution of this involvement.

Subclinical left ventricular abnormalities in young diabetics

Twenty young asymptomatic diabetic patients were evaluated for left ventricular dysfunction by determining the radionuclide ejection fraction response to supine bicycle ergometry. The double product at peak exercise (28,743 +/- 3,314 vs 29,007 +/- 3,625, p greater than .05) was not significantly different between the two groups. Seven of 20 diabetics had either no change or a drop in their ejection fraction during exercise while 1 of 20 control subjects had no change in ejection fraction. There was no correlation between the FBS (r = .26) and HbA1c (r = .32) and ejection fraction change during exercise, although those diabetics with LV dysfunction tended to have a higher HbA1c level as compared to diabetics with a normal response (16.8 +/- 3.1 percent vs 12.5 +/- 3.8 percent respectively, p greater than .05). The LV systolic dysfunction in young asymptomatic diabetic subjects does not appear to correlate with the degree of acute or chronic hyperglycemia, and therefore, is not a direct function of the dynamic metabolic state of diabetes.

Ultrastructural alterations in cardiac muscle of diabetic BB Wistar rats

The cardiac muscle of BB Wistar rats suffering from diabetes for 8 and 16 weeks (8-Wk and 16-Wk of DM) were examined by light and electron microscopy. The diabetic rats were kept alive by injections of small doses of insulin and exhibited severe hyperglycaemia, glycosuria and weight loss. The heart/body weight ratio of all diabetic groups was greater than that of age matched controls. Over the experimental period, the left ventricular myocardium of the diabetic BB rats sustained damage that was progressively more serious with the duration of the diabetic state. In BB rats after 8-wk of diabetes the myocardium contained large numbers of lipid droplets and glycogen granules around mitochondria which showed patchy swelling, and slight loss of myofilaments. Disruption of mitochondrial membranes and extensive loss of myofilaments were seen in rats diabetic for 16 wk. In addition, dilatation of the sarcoplasmic reticulum-transverse tubular system, formation of a contraction band and myelin bodies and widening of the intercellular space at the fasciae adherens of the intercalated disc were characteristically observed in BB rats after 16-wk of diabetes. However, there were no evident alterations in the capillaries of any diabetic BB rats. Morphometric analyses showed the volume percentage of myofibrils in diabetic rats to be significantly decreased when compared with controls. The loss of myofibrillar elements may be a primary damage induced by insulin deficiency. The formation of contraction bands suggests Ca2+ overload caused by diabetic metabolic disturbances.

Diabetes-induced abnormalities in the myocardium

One of the leading causes of mortality in diabetics is myocardial disease. In the past few years this subject has generated a significant amount of interest with the result that myocardial problems associated with diabetes are far better understood. Though originally thought to occur as a result of atherosclerosis, various studies have shown that heart disease can occur in the absence of atherosclerosis, suggesting a diabetic cardiomyopathy. Using diabetic animals, it has been possible to characterize diabetes-induced myocardial abnormalities. Diabetic rat hearts do not respond to conditions of high stress as well as controls. The functional depression is accompanied by altered cardiac enzyme systems. A decrease in myosin ATPase activity which appears to be a result of diabetes-induced hypothyroidism is seen. Also, a depression of sarcoplasmic reticular calcium ATPase, along with a depression of calcium uptake by the SR, is seen in diabetic rat hearts. Na+, K+ ATPase activity has also been shown to be depressed and the depression appears to correlate with depressed atrial contractility. High levels of circulating fats in diabetics may alter the integrity of membranes leading to altered enzyme activities. Insulin treatment has been relatively successful at reversing or preventing myocardial changes in the diabetic rat. Other treatments that have been studied include thyroid hormone treatment, since the depression of myosin ATPase can be corrected by such treatment; and carnitine treatment, as the elevation of long chain acyl carnitines (LCAC) and the resulting depression of calcium uptake in the SR can be so normalized. These treatments have not been successful at normalizing cardiac function. A combination of the two treatments normalized function only partially, suggesting that factors besides myosin ATPase and SR calcium uptake are involved. Other treatments that have been tried include vanadate, methyl palmoxirate, and choline and methionine. Vanadate treatment has proved to be encouraging in that it normalizes both function and hyperglycemia. Methyl palmoxirate, a fatty acid analog, normalized only the elevation of LCAC but did not affect function. Methionine and choline were only partially successful in preventing the functional alterations of diabetic rat hearts. The purpose of the present article is to review our understanding of diabetes-induced myocardial problems and their possible causes. Findings from our laboratory and others are described in which attempts have been made to normalize cardiac function.

Arrhythmia susceptibility and myocardial composition in diabetes. Influence of physical conditioning

Abnormal myocardial composition in diabetes mellitus has been described, but the effects on ventricular vulnerability have not been defined. We have assessed the susceptibility to arrhythmias in a canine model after 1 yr of mild diabetes induced by alloxan. Since physical conditioning can affect metabolic abnormalities in diabetes, this intervention has also been evaluated. Group 1 served as controls and groups 3 and 4 were diabetic. Animals in the latter group as well as nondiabetic controls of group 2 were exercised on a treadmill for the last 8 mo of the experiment. After 1 yr, anesthesia was induced with chloralose for vulnerability studies. The ventricular fibrillation threshold of 24.4 +/- 1.9 mA in group 3 was significantly less than in normals (45.1 +/- 2.2). Spontaneous arrhythmias were also more prevalent in diabetics during acute ischemia (group 3-A). Increased ventricular vulnerability after epinephrine infusion was present in the sedentary diabetes despite normal ventricular function responsiveness. In a superfused preparation of myocardium, resting membrane potential and action potential amplitude were normal in diabetics, and beta-adrenergic stimulation shortened repolarization more than in controls. Myocardial collagen concentrations, which included an interfibrillar distribution on morphologic examination, were increased in group 3. In the trained diabetics of group 4 the basal vulnerability thresholds and responses to epinephrine were normal. While myocardial collagen levels were normal, cholesterol and triglyceride increments persisted. Thus, in mild experimental diabetes, enhanced susceptibility to arrhythmias exists; this susceptibility may be based on a combination of nonhomogenous collagen accumulation affecting local conduction and increased electrophysiologic sensitivity to catecholamines.

Diabetic cardiomyopathy

Diabetes mellitus is associated with a specific cardiomyopathy. This is evident from the clinical-pathological work and the epidemiologic data from the Framingham study. Noninvasive studies of diabetics have shown alterations in systolic and diastolic function that may ultimately lead to clinical heart failure. The relationship of these cardiac changes to the type of diabetes, its duration, and its severity is not settled. However, a correlation between changes in heart function and other complications of diabetes has been demonstrated. Insufficient prospective data is available from noninvasive studies to establish the frequency of progression from subclinical cardiac dysfunction to overt congestive failure. The pathogenesis of this disorder is still uncertain. Pathological studies have shown changes in the intramural arteries, arterioles, and capillaries but their functional significance is uncertain. Experimental studies have shown interstitial changes leading to an apparently less compliant left ventricle in the diabetic dog and monkey. In the diabetic rat reversible changes were found in myocardial function, related to changes in contractile proteins and intracellular calcium metabolism. In both species, the response to anoxia or ischemia was altered in the presence of diabetes. However, irreversible depression of the contractile element was not found in most animal studies of isolated diabetes. In contrast, the combination of hypertension and diabetes leads to substantial cardiac damage and circulatory congestion, both in clinical and experimental investigations. Clearly much more work must be carried out to understand the pathogenesis, treatment, and ultimately the prevention of diabetic cardiomyopathy.

Fatty acid-membrane interactions in isolated cardiac mitochondria and erythrocytes

The effects of long-chain fatty acids on mitochondrial functions and red cell stability were studied. In albumin-containing incubation media, fatty acid distribution between the albumin-bound and the unbound fraction was estimated by calculation. When fatty acids are compared to one another on the basis of identical unbound concentrations, their effectiveness differs by orders of magnitude. Fatty acids stimulate mitochondrial basic oxygen consumption, thus lowering the respiratory control index, without changing the ATP/O ratio at lower concentrations. Lower concentrations increase Ca2+ uptake velocity, but decrease maximal Ca2+ storage capacity. The order of effectiveness of different fatty acids is the same for both oxidative phosphorylation and Ca2+ uptake. The influence of fatty acids on red cell stability in hypotonic media is similar to these effects both in concentration range and in order of effectiveness. The influence of fatty acids on red cell stability and their critical micellar concentrations were investigated because these are general characteristics of 'detergent-like' compounds. Critical micellar concentrations of the fatty acids in physiological salt buffers are, in general, at least 10-fold higher than the concentrations exhibiting membrane effects in vitro. Based on these findings it is suggested that, of the various concentrations reported in literature for myocardial non-esterified fatty acids, only the lowest values are physiologically possible.

Are pressure-volume relations at end-systole a reflection of left ventricular myocardial contractility?

The pressure-volume relation at end-systole is reportedly altered by changes in contractility. To explore the potential of this ratio in man 185 subjects including 23 normals (Group I) were studied. In 35 patients of Group II (16 with mitral stenosis, 7 with atrial septal defect, and 12 with cor pulmonale) ESP/ESV like an index of contractility measuring force-velocity-length rela tionship (Cy Ix) was insignificantly different from Group I (ESP/ESV and Cy Ix in I = 1.73 ± .31 mmHg/sec, 1.46 ± .09 cm/sec/cm vs 1.44 ± .10, 1.31 ± .05 in II respectively.) With significantly reduced Cy Ix (1.03 ± .04, P<0.00001) ESP/ ESV was likewise reduced (1.16 ± .07, P<0.007) in 108 patients with compen sated LV disease (34 with alcoholic cardiomyopathy, 16 coronary artery dis ease, 30 aortic valve disease, 8 hypertension and 16 with other heart muscle disease.) Like the Cy Ix (0.70 ± .05, P<0.001) ESP/ESV was even lower (0.84 ± .13, P<0.05) in 14 patients with decompensated LV (Group IV). It was insensitive to changes in pressure (angiotensin and volume (dextran). However unlike the Cy Ix it did not vary with acute changes in inotropy (exercise and pacing).

The correlations between ESP/ESV and ejection fraction and contractility index in the entire series though weak, were significant (r = .50 and .20 respectively, each P<0.006). Exclusion of patients with aortic valve disease and hypertension in the analysis tended to improve the relationship between the contractility and end-systolic pressure-volume parameters. In the latter two subgroups neither the ESV nor the ESP/ESV ratio related to the contractil ity index, both parameters however did correlate significantly with the ejection fraction. These results indicate that end-systolic pressure-volume relations provide useful measures of LV performance in man, though not expressing the contractility either in all patients or under all situations.

Hypertensive diabetic cardiomyopathy in the rat: ultrastructural features

We previously described a cohort of diabetic patients with typical congestive cardiomyopathy, in whom myocardial lesions were related to concomitant high blood pressure. To evaluate the association of diabetes mellitus and hypertension in more detail, we studied 4 groups of rats with either no disease, streptozotocin-induced diabetes mellitus, renovascular hypertension, or a combination of hypertension and diabetes. Analysis revealed significant myocardial fibrosis and degeneration in the hypertensive-diabetic group when compared to controls, without an obvious relationship to small vessel lesions. The myocardial alterations appeared similar to those observed in patients with hypertension and diabetes mellitus. Of note, although hypertensive animals had focal moderate lesions, diabetic animals had no pathological changes. To further characterize these histological changes, we performed electron microscopy on the 4 animal groups, which we are reporting in this study. Our analysis of the ultrastructural alterations confirms the previous histological observations. Diabetic animals only had increased cellular lipid, and mild, focal areas of myofibrillolysis, with no significant increases in perivascular and perisarcolemmal basal lamina. Consistent with our light microscopic finding that PAS positive material was associated with interstitial or replacement fibrosis, we noted basal lamina proliferation in the hypertensive and hypertensive-diabetic groups, particularly in areas of scarring. Pericapillary basal lamina was increased to the greatest extent in the hypertensive-diabetics. Qualitative alterations of myocardial cells and muscular blood vessels were similar in both the hypertensive and hypertensive-diabetic animals; however, there were more extensive changes in the latter group. This study provides further evidence that the combination of diabetes mellitus and hypertension produces significantly greater myocardial lesions than with either disease alone, not only at the light microscopic level, but ultrastructurally as well. Although the pathogenesis of this cardiomyopathy is unknown it may be related to abnormalities of the cardiac microcirculation. The prevalence of hypertension in the diabetic population suggests that greater attention should be paid to the combination of these 2 conditions and their effects on the heart.

Assessment of fatty acids in dog left ventricular myocardium

The concentration and composition of fatty acids in four lipid classes in biopsies of dog left ventricular myocardium were determined, using gas-liquid chromatography. When precautions were taken to minimize lipolysis during storage of the tissue and the homogenization process, the following results were obtained: 29 +/- 10 nmol non-esterified fatty acids, 2.98 +/- 2.41 mumol triacylglycerol, 149 +/- 51 nmol cholesteryl esters and 23.76 +/- 3.38 mumol phospholipid (expressed as fatty acid moiety per gram of wet tissue). The concentration of non-esterified fatty acids was 15 to 300 times lower than reported in literature. The main constituents of the non-esterified fatty acids were palmitic, stearic and oleic acid. Triacylglycerol consisted of approximately 40% esterified oleic acid. Linoleic acid accounted for 40% of the fatty acids in the cholesteryl-esters class. More than half of the fatty acid moiety of total phospholipids was linoleic acid and arachidonic acid.