Pharmacological intervention in acute myocardial ischemia and reperfusion

Simultaneous increase in germ cell apoptosis and oxidative stress under acute unilateral testicular ischaemia in rats

Ischaemia induced germ cell apoptosis in rat testis was studied in detail to find out (i) spermatogenic stage or seminiferous epithelium region specific involvement of germ cells in apoptosis, (ii) preferential specificity of a particular germ cell type to become apoptotic and (iii) the ratio of live and dead testicular cells isolated in vitro after various period of ischaemic induction. Cell apoptosis, as observed in histological sections increased from 1 to 24 h of ischaemia. Apoptosis was not restricted to any specific germ cell type but was observed simultaneously in all the cell types in the initial hours (1-6 h) of ischaemia. No spermatogenic stage specific preference in apoptotic induction was also observed. However, as the duration of ischaemia progressed, the cell types observed to be most affected in number and morphology were the spermatids followed by spermatocytes. Centrally located tubules of testis were affected first than those located in the periphery. Overexpression of Bax staining was limited to few germ cell nuclei only. More than 95% of the germ cells in the control testis that earlier showed trypan blue dye exclusion were found stained after 12 h of ischaemia. Starting from early hours (1 h), lipid peroxidation rose proportionally with the duration of ischaemia while superoxide dismutase (SOD) and catalase activities were found decreased. Significant (p < 0.05) increase in the activities of glutathion-s-transferase and levels of hydrogen peroxide were observed after 6 h of ischaemia. These findings indicate that the physiological processes of oxidative stress have a direct linkage to the extent of germ cell apoptosis in the seminiferous epithelium.

The effect of metformin on insulin receptors and lipid peroxidation in alloxan and streptozotocin induced diabetes

Biguanides are used for the treatment of non-insulin dependent diabetes mellitus but there is no evidence for an improving action of biguanide on the enhancement of peripheral glucose disposal in type 1 diabetes. It is known that biguanide agents reduce the oxidation of free fatty acids. Using alloxan and streptozotocin (STZ) induced diabetic rats as a model for type 1 diabetes mellitus, we measured insulin binding capacity and plasma lipid peroxidation levels before and after metformin induction. There was a significant increase in insulin binding capacity and lipid peroxidation levels in alloxan and STZ diabetes compared to controls. We examined the effect of metformin on alloxan and STZ-induced diabetic rats. In alloxan-induced diabetes metformin (Met) treatment led to an increase in insulin receptor number in liver plasma membranes (before Met: 46.50 +/- 2.69, after Met: 76.00 +/- 3.39 fmol/mg, p < 0.001) and a decrease in plasma lipid peroxidation levels compared to the non-treated group (before Met: 1.85 +/- 0.53, after Met: 1.10 +/- 0.09 nmol MDA/ml, p < 0.05). In STZ-induced diabetic rats metformin treatment did not change the lipid peroxidation levels (before Met: 1.26 +/- 0.31, after Met: 1.38 +/- 0.44 nmol MDA/ml, p > 0.05) whereas it did increase the receptor numbers (before Met: 41.60 +/- 4.33, after Met: 63.40 +/- 8.64 fmol/mg, p < 0.002).

Free radical activity in type 2 diabetes

Free radical activity has been implicated in the development of diabetic vascular complications in Type 1 diabetes. The aim of the present study was to investigate the levels of free radical scavengers, particularly erythrocyte superoxide dismutase, plasma and erythrocyte lysate thiol, and caeruloplasmin in 22 Type 2 diabetic patients clinically free of complications, and 15 comparable non-diabetic control subjects. The concentration (median (range] of both superoxide dismutase (23 (10-39) vs 45 (25-75) mumol l-1; p less than 0.001) and plasma thiol (374 (172-523) vs 460 (386-595) mumol l-1; p less than 0.01) were reduced in the diabetic group. There were no significant differences in the concentration of erythrocyte lysate thiol (199 (114-520) vs 188 (114-328) mumol l-1) or plasma caeruloplasmin (18 (9-31) vs 24 (6-50) mumol l-1) between the groups. This reduction in superoxide dismutase and the imbalance in the redox status of the plasma and lysate thiol demonstrated is consistent with an increase in free radical activity in Type 2 diabetes.

Recovery of hypertrophied rat hearts after global ischemia and reperfusion at different perfusion pressures

The ability to resist transient ischemia was studied in isolated hearts of 18 months old spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. Both types of hearts showed optimal performance during the preischemic period when perfused at a diastolic perfusion pressure of 8.0 (WKY) and 13.3 (SHR) kPa. Hemodynamic recovery of WKY hearts during reperfusion at 8.0 kPa, following 45 min global ischemia, was satisfactory. coronary perfusion completely normalized, contractility (dPlv/dtmax) was slightly depressed and cardiac output returned, on the average, to 40% of the preischemic values. In contrast, hemodynamic function of SHR hearts reperfused at 13.3 kPa was greatly depressed, as evidenced by almost complete abolition of cardiac output, severe reduction of dPlv/dtmax and persistent underperfusion of the endocardial layers. In addition, the postischemic release of lactate dehydrogenase was retarded and enhanced. The release patterns of degradation products of adenine nucleotides showed a shift to the endstage products xanthine and uric acid. The enhanced vulnerability of the hypertrophied heart to ischemia was even more expressed when the SHR hearts were reperfused at 8.0 kPa. Postischemic function was characterized by electrical instability, loss of contractility and cardiac output, and noreflow in the endocardial layers. Persistent accumulation of lactate and degradation products of adenine nucleotides in the postischemic hearts are in line with the lack of reperfusion. The present results indicate that a detailed mechanistic explanation for the reduced ability to withstand ischemia of SHR cannot be based on differences in ATP content or an altered anaerobic glycolitic activity prior and during ischemia. It is suggested that a defect on the circulatory level, probably caused by enhanced reactivity of the coronary vessels towards ischemia-elicited factors, is responsible for the higher vulnerability of hypertrophied heart to an ischemia insult.

Effects of pyruvate on post-ischemic myocardial recovery at various workloads

In the present study the hemodynamic and metabolic effects of pyruvate (5 mM), added as cosubstrate to glucose (11 mM) perfused, transiently ischemic, isolated working rat hearts, were evaluated. During 2 h of normoxic perfusion pyruvate improved functional stability, prevented depletion of glycogen and triacylglycerol stores, and increased non-esterified fatty acid (NEFA) levels, even at relatively high workloads. The elevated NEFA levels are in line with the notion that pyruvate competes with endogenously produced fatty acids for oxidative energy production. After 45 min of global ischemia pyruvate was found (a) to affect markedly the relative contribution of ATP, ADP and AMP to the total adenine nucleotide content and (b) to stimulate the degradation of glycogen and to enhance the accumulation of lactate, suggesting enhanced anaerobic ATP production. After restoration of flow pyruvate reduced the incidence of fibrillation and markedly improved recovery of cardiac output at both normal and high workload. Pyruvate did neither attenuate the release of lactate dehydrogenase, a marker for cell death, nor improve the conservation of the total adenine nucleotide and ATP content of hearts reperfused for 30 min. The latter findings indicate that hemodynamic recovery during reperfusion in the presence of pyruvate is neither related to the absolute tissue content of ATP nor to a reduction of irreversible cell damage, and suggest that pyruvate exerts its advantageous hemodynamic effects rather by improving the condition of reversibly damaged cells during reperfusion.

Leukotriene-mediated liver injury

The pathogenic mechanism of fulminant hepatitis induced by 700 mg/kg D-galactosamine plus 33 micrograms/kg endotoxin was investigated in male NMRI mice. The extent of liver injury was assessed by measurement of serum transaminases and sorbitol dehydrogenase activities 9 hr after intoxication, as well as by histopathological evaluation. When the hepatic glutathione content of galactosamine endotoxin-treated animals had been decreased by more than 90% following administration of 250 mg/kg phorone or 400 mg/kg diethyl maleate given three times, no signs of liver injury were observed. Since different agents interfering with the leukotriene synthesis pathway also prevented galactosamine/endotoxin-induced hepatitis, we suspected that a glutathione-derived peptidoleukotriene may be the pathogenic metabolite. In vivo inhibition of the catabolism of leukotriene C4 by administration of 50 mg/kg of the glutamyl transpeptidase inhibitor AT 125 (Acivicin) also protected the animals against liver injury. In order to elucidate which metabolite of leukotriene C4 was responsible for the observed hepatotoxicity we intravenously injected leukotrienes into animals that had received only galactosamine. Injection of 50 micrograms/kg leukotriene E4 1 hr after galactosamine had no effect. The same dose of leukotriene D4 led to a fulminant hepatitis which was prevented when the leukotriene D4 antagonist FPL 55712 had been given before. In contrast, lipoxygenase inhibitors or AT 125 did not protect against galactosamine + LTD4. Galactosamine/endotoxin-induced and galactosamine/leukotriene D4-induced hepatitis resulted in similarly localized histopathological changes, i.e. diffuse necrosis in the organ. We conclude from our results that galactosamine/endotoxin-induced hepatitis is mediated by a leukotriene D4-dependent mechanism.

Evidence for the involvement of a reperfusion injury in galactosamine/endotoxin-induced hepatitis in mice

Simultaneous intraperitoneal administration of 700 mg/kg galactosamine and 33 micrograms/kg Salmonella abortus equi endotoxin to male NMRI albino mice resulted in fulminant hepatitis as assessed after nine hours by measurement of serum transaminases as well as sorbitol dehydrogenase activities. Intraperitoneal pretreatment of animals with 2 X 100 mg/kg allopurinol, or intravenous pretreatment with 33 kU superoxide dismutase or 1 MU catalase fully prevented hepatitis. Administration of 10 micrograms/kg of the prostacyclin analogue iloprost antagonized liver injury when given simultaneously with galactosamine/endotoxin but did not protect when given 90 min later. Tocopherol or desferal pretreatment of the animals had no significant protective effect. Together with our recent finding that hepatic leukotriene D4 production is likely to be responsible for galactosamine/endotoxin-induced hepatitis we interpret these results as evidence for a leukotriene-induced hepatic ischemia followed by a reperfusion syndrome.

Coronary artery stenosis controlled by distal perfusion pressure: description of the servo-system and time-dependent changes in regional myocardial blood flow

An animal model for the induction of coronary artery stenosis is described. In this model the degree of stenosis, as induced with commercially available hydraulic occluders, can be easily controlled by keeping constant the mean perfusion pressure (pcor) distal to the site of stenosis. This pcor is the input signal for a servo-system feeding a motor-pump, which determines the degree of inflation of the cuff around the left anterior interventricular coronary artery (LAICA). In each experiment pcor did not vary more than 2 mm Hg from the preset value of about 25 mm Hg. In 60 anesthetized open-chest dogs the time course of standard hemodynamic variables and regional myocardial blood flow in the center of the underperfused area, using the radioactive microsphere technique, were determined. Within 1 min after induction of stenosis heart rate and end-diastolic left ventricular pressure (plved) increased (by 20 and 60%, respectively) and mean aortic pressure and dplv/dtmax decreased (by 10 and 25%, respectively). After the initial decrease median myocardial blood flow further decreased between 1 and 5 min of stenosis from 0.63 to 0.32 ml.min-1.g-1 in the outer layers (P less than 0.05) and from 0.26 to 0.15 ml.min-1.g-1 in the inner layers (P less than 0.05), despite constant hemodynamic conditions and pcor. Between 5 and 120 min of stenosis these values remained unchanged in the outer layers, but decreased further in the inner layers to 0.08 ml.min-1.g-1 (P less than 0.05). The accurate control of pcor, the reproducibility of the levels of residual blood flow and the ease of handling the stenosis system indicate that coronary artery stenosis controlled by perfusion pressure distal to the stenosis is a useful animal model to study events during regional myocardial ischemia. With the use of this model of low flow ischemia a biphasic increase of myocardial vascular resistance was observed, which is initiated during the first minutes of coronary artery stenosis.

Tissue protection by allopurinol in the myocardial calcium paradox

The aim of the present study was to evaluate the protective properties of the xanthine oxidase inhibitor allopurinol in the myocardial calcium paradox. Two injury levels, minimal and total calcium paradox, caused by different volumes (5 ml and 45 ml) of calcium-free perfusion (5 min) prior to calcium repletion (15 min) were examined +/- allopurinol (0.15 mmol/l) in the normothermic isolated rat heart model. Allopurinol supplementation (5 min prior to, during and 5 min following Ca2+-free perfusion) had no effect upon tissue injury in the total calcium paradox, but afforded considerable protection as assessed by enzymatic, physiologic, and metabolic parameters in the minimal calcium paradox. When allopurinol was omitted during calcium repletion, tissue protection was less apparent. The presence of verapamil (2 mumol/l) in addition to allopurinol (5 min prior to, during, and 5 min following calcium depletion) afforded only a marginal further protection in the minimal calcium paradox. It is concluded from the present study that tissue protection by allopurinol in the calcium paradox is limited to minimal or less severe calcium paradox models and that the protective action of allopurinol may indicate an inhibition of the xanthine oxidase reaction and the generation of free oxygen radicals.

The effect of diltiazem on myocardial recovery after regional ischemia in dogs

The effect of diltiazem on post-ischemic metabolic and functional recovery was investigated in regionally ischemic dog hearts. The duration of ischemia was 60 min, followed by 60 min of reperfusion. Diltiazem (bolus injection of 0.1 mg X kg-1 body weight prior to ischemia, followed by a continuous infusion of 0.1 mg X kg-1 X h-1) had no effect on residual coronary flow in the centre of the ischemic area, but blunted the reactive hyperemia response after restoration of flow. The drug partially prevented the depletion of ATP and glycogen in the severely underperfused subendocardial layers, i.e. when residual flow was below 0.1 ml X min-1 X g-1. Reduction of the content of these substances in the subepicardial layers was moderate and not influenced by diltiazem. Segment shortening in the subepicardial layers disappeared whereas segment lengthening was observed in the subendocardial layers during the ischemic period. Diltiazem did not prevent the loss of contractile function. Despite an initial restoration of contractile function within 10 min after reperfusion, no significant beneficial effect of diltiazem treatment on mechanical function of the reperfused area was present thereafter.