Robert L. Engler

Reperfusion injury induces apoptosis in rabbit cardiomyocytes.

The most effective way to limit myocardial ischemic necrosis is reperfusion, but reperfusion itself may result in tissue injury, which has been difficult to separate from ischemic injury. This report identifies elements of apoptosis (programmed cell death) in myocytes as a response to reperfusion but not ischemia. The hallmark of apoptosis, nucleosomal ladders of DNA fragments (approximately 200 base pairs), was detected in ischemic/reperfused rabbit myocardial tissue but not in normal or ischemic-only rabbit hearts. Granulocytopenia did not prevent nucleosomal DNA cleavage. In situ nick end labeling demonstrated DNA fragmentation predominantly in myocytes. The pattern of nuclear chromatin condensation was distinctly different in reperfused than in persistently ischemic tissue by transmission electron microscopy. Apoptosis may be a specific feature of reperfusion injury in cardiac myocytes, leading to late cell death.

Differing circadian patterns of symptom onset in subgroups of patients with acute myocardial infarction.

Circadian variation of the onset of acute myocardial infarction has been noted in many studies and may carry important pathophysiologic implications. However, only a few previous studies have attempted subgroup analyses. In 4,796 patients with documented acute myocardial infarction, the time of symptom onset was recorded. As in other studies, the peak of onset occurred in the morning from 6:01 AM to 12:00 noon, and 28% of the population (1.16 times the average percentage for the other time periods) experienced symptom onset in that period (p less than 0.001). There was a second, lower peak (25%) in the evening between 6:01 PM and 12:00 midnight, which was also observed in some previous studies. We sought to determine whether or not the presence of subgroups with specific clinical characteristics would exhibit different patterns and thereby contribute to these peaks in the overall population. In patients with a history of congestive heart failure (n = 606) or with non-Q wave infarction (n = 832), a pronounced peak (29%) occurred only in the evening. Two nearly equal peaks were observed in patients older than 70 years of age (n = 1,422), smokers (n = 2,057), diabetics (n = 767), women (n = 1,213), and patients taking beta-blocking drugs (n = 847). Finally, in patients with a previous myocardial infarction (n = 1,104), no peaks were observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased adenosine concentration in blood from ischemic myocardium by AICA riboside. Effects on flow, granulocytes, and injury.

Morbidity and mortality from acute coronary artery occlusion may be reduced if local myocardial adenosine concentration is augmented because 1) coronary collateral blood flow during ischemia increases with adenosine infusion, and 2) granulocytes that accumulate in the microcirculation during ischemia are, to a large extent, inhibited by adenosine from generating superoxide anion free radicals, from adhering to vascular endothelium, and from damaging endothelial cells in culture. Using a cultured lymphoblast model system, we found that 5-amino-4-imidazole carboxamide (AICA) riboside enhanced adenosine accumulation during ATP catabolism. Therefore, AICA riboside pretreatment was used in canine myocardium to selectively increase adenosine concentration in the ischemic area during 1 hour of ischemia. At 5 minutes of ischemia, endocardial flow to ischemic myocardium in saline-treated and AICA riboside-treated dogs was 0.06 +/- 0.03 and 0.34 +/- 0.11 ml/min/g, respectively (p less than 0.01); flow to nonischemic myocardium was not affected. Ventricular tachycardia and premature ventricular depolarizations were significantly attenuated in the AICA riboside-treated dogs. Blood pressure and heart rate were not affected by AICA riboside. In venous blood from ischemic tissue, adenosine increased from undetectable levels (less than 0.01 microM) to 0.22 +/- 0.08 microM in saline and 1.79 +/- 0.06 microM in AICA riboside-treated dogs, respectively (p less than 0.001). Coronary vein inosine concentrations were greater in saline than in AICA riboside-treated dogs. In separate in vitro studies, AICA riboside did not alter the removal rate of adenosine from canine blood. Indium-labeled granulocyte accumulation was significantly less in ischemic myocardium in AICA riboside-treated compared with saline-treated dogs. In addition, adenosine, but not AICA riboside, inhibited in vitro canine granulocyte superoxide production. We conclude that AICA riboside given before myocardial ischemia augments adenosine concentration, decreases arrhythmias, decreases granulocyte accumulation, and improves collateral flow to ischemic myocardium. One of the beneficial mechanisms could be an increased production of adenosine rather than inosine from ATP catabolism that causes vasodilation and inhibition of granulocytes. We propose a new hypothesis regarding regulation of the inflammatory reaction to ischemia in the microcirculation. Adenosine, in addition to its vasodilator action, is an anti-injury autacoid that links ATP catabolism to inhibition of granulocyte adherence, microvascular obstruction, and superoxide anion formation.

Pharmacologic and Hemodynamic Influences on the Rate of Isovolumic Left Ventricular Relaxation in the Normal Conscious Dog

We studied the effects of acute pharmacologic and hemodynamic interventions on isovolumic left ventricular relaxation in 19 conscious dogs using micromanometer tip catheters. Isoproterenol (11 studies) augmented peak rate of rise of left ventricular pressure [(+) dP/dt] by 1,275+/-227 (SE) mm Hg/s (P < 0.001) and dP/dt at an isopressure point of 35 mm Hg during isovolumic relaxation [(-) dP/dt(35)] by 435+/-80 mm Hg/s (P < 0.001). Peak (-) dP/dt decreased by 467+/-89 mm Hg/s (P < 0.002). The time constant, T, derived from the logarithmic fall of pressure during isovolumic relaxation, shortened from 20+/-2.8 to 14.9+/-1.8 ms (P < 0.003). Calcium (11 studies) increased peak (+) dP/dt and (-) dP/dt(35) (both P < 0.0001); peak (-) dP/dt was unchanged. T shortened from 20.4+/-1.8 to 17.3+/-1.5 ms (P < 0.002). Volume (13 studies) did not affect either dP/dt or T. Phenylephrine (13 studies) augmented peak (-) dP/dt, but reduced (-) dP/dt(35) (both P < 0.01); T lengthened from 22.1+/-1.5 to 32.5+/-1.5 ms (P < 0.01). In 15 studies, rapid atrial pacing increased peak (+) dP/dt and (-) dP/dt(35) (both P < 0.01). In the first post-pacing beat, peak (-) dP/dt and (-) dP/dt(35) decreased (both P < 0.01), although peak (+) dP/dt increased further. T paralleled values of (-) dP/dt(35). In five dogs, beta adrenergic blockade had no significant effect on any variable after calcium, volume, or phenylephrine infusion or during or after atrial pacing when the pre-and post-propranolol states were compared. We conclude that positive inotropic interventions augment both left ventricular contraction and relaxation. The changes in isovolumic relaxation are independent of alterations in sympathetic tone produced by beta-adrenergic blockade. Peak (-) dP/dt may not be a valid measure of left ventricular relaxation rate during acute alterations in inotropic state or afterload.

Apoptosis in Myocardial Ischemia‐Reperfusion

Abstract: The signal transduction pathways by which ischemia‐reperfusion leads to apoptosis may involve the JNK pathway, ceramide generation, and inhibition of protective PKC pathways. The biochemical events associated with apoptosis include mitochondrial inactivation, cytochrome c dislocation, caspase activation, and cytoplasmic acidification. Through the concerted efforts of multiple classes of enzymes, apoptosis is accomplished, resulting in the death of a cell in which potentially transforming oncogenes have been degraded and inflammatory contents are contained within the plasma membrane until the fragments can be ingested by phagocytes. This non‐inflammatory mode of cell death permits tissue remodeling with minimal scar formation, and so is preferable to necrotic cell death. The distinction between apoptosis and necrosis, which implies different mechanisms of cell death, is blurred in the case of a pathologic insult such as ischemia‐reperfusion. It is suggested that it is more useful to view cell death in the context of whether or not it can be prevented

Granulocytes and no-reflow phenomenon in irreversible hemorrhagic shock.

Recent evidence shows that circulating granulocytes play an important role in capillary stasis and tissue injury. We investigated two aspects of the problem in a Wiggers hemorrhagic shock model of the rat: the survival rate and the microvascular no-reflow phenomenon. A conventional group of rats with normal blood cells and a neutropenic group of rats pretreated with intraperitoneal antigranulocyte antibody were used to evaluate the effects of granulocytes. Two hemorrhagic shock protocols (HSP) were carried out. In HSP-1, the rats were subjected to 40 mm Hg mean arterial pressure for 3 hours. The conventional group (n = 11) showed a 36% survival rate compared with 100% in the neutropenic group (n = 6). In HSP-2, the hypotension was more severe, 30 mm Hg mean arterial pressure for 7 hours. There were no survivors in the conventional group (n = 8), compared with a 100% survival rate in the neutropenic group (n = 6). The extent, location, and mechanism of the no-reflow phenomenon was investigated by examining histological sections from several organs after infusion of a contrast medium to mark vessels with flow in a control group without shock and in the HSP-2 model 2 hours after blood replacement. The arterioles and venules uniformly contained contrast medium in all three groups; only capillaries showed no-reflow. A significantly higher percentage of no-reflow was observed in the capillaries of the conventional shock group than in the neutropenic shock group. We concluded that the obstruction of capillaries was largely due to trapped granulocytes, suggesting that these leukocytes play a key role in the capillary no-reflow phenomenon and survival from hemorrhagic shock.

Measurement of left ventricular ejection fraction by mechanical cross-sectional echocardiography.

Cross-sectional echocardiography is a new noninvasive technique for imaging the heart. We developed a method for using mechanical cross-sectional echocardiograms (sector scans) to determine left ventricular volumes and ejection fraction. Using left ventricular cineangiography as a standard, sector scan ejection fraction correlated better (r = 0.93) than M-mode echocardiography by any of three established methods, and the sector scan regression line did not differ from the line of identity (p > 0.33). Interobserver variability for sector scan ejection fraction was 2.3 i 1.2% (mean ± SD). Variation between two studies performed within 24 hours and analyzed by the same observer was 1.4 ± 1.5%. However, the sector scans consistently underestimated left ventricular end-diastolic volume. We conclude that sector scan echocardiography is more reliable than conventional M-mode techniques for estimating left ventricular ejection fraction, but estimation of left ventricular end-diastolic volume is unreliable with the methods currently available.

Influence on prognosis and morbidity of left ventricular ejection fraction with and without signs of left ventricular failure after acute myocardial infarction

The left ventricular (LV) ejection fraction (EF) is known to be an independent predictor of late prognosis after acute myocardial infarction. Despite a previous report that early heart failure (evidenced only by advanced pulmonary rales in the hospital) can predict prognosis in the absence of severe depression of the LVEF at hospital discharge, the potentially strong influence of various measures of in-hospital heart failure on the predictive ability of LVEF has not been generally appreciated. Accordingly, in 972 patients with acute myocardial infarction the effect on late mortality of the presence or absence in-hospital of both clinical and radiographic signs of LV failure in subgroups of patients with normal, moderately or severely depressed LVEF was examined and measured close to hospital discharge. Patients were divided into 3 groups according to LVEF: group I LVEF less than or equal to 40, n = 265; group II LVEF 0.41 to 0.50, n = 241 and group III LVEF greater than or equal to 0.51, n = 466. When clinical signs of LV failure were present at any time during the coronary care unit period, the 1-year mortality rate after hospital discharge in groups I, II and III was 26, 19 and 8%, compared with 12% (p less than 0.01), 6% (p less than 0.01) and 3% (p less than 0.02), respectively, when signs of LV failure were absent.(ABSTRACT TRUNCATED AT 250 WORDS)

Sulfonylurea KATP Blockade in Type II Diabetes and Preconditioning in Cardiovascular Disease

I n the early 1970s, the UGDP assessed the efficacy of oral hypoglycemic treatment in comparison with insulin and diet alone in the prevention of vascular complications. The surprising finding was the appearance of a significantly higher cardiovascular mortality in patients on oral hypoglycemic agents (sulfonylureas) compared with those on diet alone. Nonetheless, these agents are used extensively because, one suspects, of a lack of a plausible mechanism for the UGDP study results. In 1983, the KATP was discovered and was demonstrated to be sensitive to the sulfonylurea class of drugs; ie, these agents block the opening of this channel. In 1986, the phenomenon of ischemic preconditioning was discovered, which demonstrated the unique ability of a sublethal period of ischemia (angina) to protect the heart from a subsequent lethal ischemic insult. In the 1990s, it became clear that one of the probable mechanisms through which this preconditioning phenomenon worked was via the opening of the KATP. New discoveries often shed light on old mysteries, and this may be the case with the sulfonylurea class of oral hypoglycemic agents. Therefore, it is timely to rethink the seemingly paradoxical result of the UGDP study. In 1942, Janbon et al1 found that sulfonamide derivatives used to treat typhoid fever caused hypoglycemia, which led to the development of a new treatment for NIDDM. Diabetes is a significant problem worldwide. For example, six million people in the United States have NIDDM (85% of all diabetics) and are eligible for treatment with these drugs. The National Disease and Therapeutic Index estimates that 54% of physician visits by these patients included a prescription for oral hypoglycemic agents and that in 1994 there were 2.5 million patient-years of treatment, accounting for

Effect of Vacuolar Proton ATPase on pHi, Ca2+, and Apoptosis in Neonatal Cardiomyocytes During Metabolic Inhibition/Recovery

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