The effects of ischemia and reperfusion on mucosal respiratory function, adenosine triphosphate, electrolyte, and water content in the ascending colon of ponies

OBJECTIVE: The purpose of this study was to examine the effects of ischemia and reperfusion on the biochemical integrity of equine colonic mucosa to assess the relative roles of ischemic- and reperfusion-induced damage. STUDY DESIGN: Two hours of no-flow ischemia experimentally induced by 720 degrees counterclockwise ascending colon volvulus followed by 2 hours reperfusion after derotation. ANIMALS: Ten ponies. METHODS: Ascending colon biopsies were obtained every hour for measurement of mucosal adenosine triphosphate (ATP), water, sodium, and potassium content. Additional samples were homogenized for assay of mitochondrial respiratory function. RESULTS: ATP content diminished 92% after ischemia and recovered to only 44% of control levels (P < .001 versus controls) after 2 hours reperfusion. Reperfusion increased mucosal water and decreased sodium and potassium content for the duration of the experiment. Both NADH-(pyruvate) and FADH-linked (succinate) respiration decreased after ischemia and did not recover during reperfusion indicating electron transport chain dysfunction. CONCLUSIONS: Two hours ischemia induced severe metabolic dysfunction in equine colon mucosa which persisted throughout reperfusion. Unequivocal evidence of injury specific to reperfusion was not observed in this study suggesting that much of the damage observed during reperfusion may be a continuation of injury induced during the ischemic period and not specific to reperfusion per se. CLINICAL RELEVANCE: This study suggests that greater efforts to metabolically support ischemically injured mucosa may be an important aspect of obtaining improved survival of horses affected by ascending colon volvulus (ACV).     

Abnormalities in oxygenation, coagulation, and fibrinolysis in colonic blood of horses with experimentally induced strangulation obstruction

OBJECTIVE: To measure arterial and venous blood gas, coagulation, and fibrinolysis variables in blood from isolated segments of control and ischemic large colons for the purpose of identifying variables for rapid, indirect assessment of colonic mucosal injury. DESIGN: Variables were determined at specific intervals during the 4-hour study (3 hours of ischemia and 1 hour of reperfusion). ANIMALS: Seven clinically normal horses between 2 and 15 years old. PROCEDURES: Horses underwent laparotomy and occlusion of the lumen and vasculature of the mid-portion of the pelvic flexure of the large colon. During ischemia of 1 randomly-chosen colonic segment, variables were measured to determine colonic mucosal damage and were compared with histologic scores of colonic biopsy specimens. RESULTS: Significant (P < 0.05) differences from control values were observed over time for venous pH, PCO2, PO2, oxygen saturation, oxygen content, arteriovenous oxygen difference, and lactate and glucose concentrations. Mean histologic scores of biopsy specimens obtained from ischemic colons were significantly (P < 0.05) greater (indicating greater damage) than those from control colons, and increased significantly (P < 0.05) with duration of ischemia. CONCLUSIONS: Venous lactate, oxygen saturation, and PO2 values were the most significant predictors of the severity of histologic damage within the ischemic colons (R2 = 0.661). CLINICAL RELEVANCE: Venous blood gas and lactate values in the large colon are good predictors of the amount of intestinal damage incurred during 3 hours of ischemia, and may be clinically useful for the rapid determination of colonic viability.     

Ginkgolides antagonizing some effects of platelet-activating factor in vitro

The mixture of platelet-activating factor (PAF) and platelets produced significant contraction of guinea pigs' bronchus, while the contraction induced by PAF alone was mild relatively, the IC50 were 6.14 x 10(-7) mol/L and 6.32 x 10(-4) mol/L respectively. There was significant difference between these two groups (P < 0.05). When the platelets were pre-incubated with ginkgolides for 10 minutes in Tris-Tyrode's buffered saline, effects of the PAF and platelets mixture were significantly inhibited (P < 0.01). Exposure of guinea pigs' bronchus to PAF in vitro resulted in a loss of beta-adrenergic receptors and responses to isoproterenol, and this effect of PAF was prevented by prior incubation of the guinea pigs' bronchus with ginkgolides (P < 0.05). The results showed ginkgolides were a potent PAF antagonist.     

Platelet-activating factor mediates pulmonary macromolecular leak following intestinal ischemia-reperfusion

Platelet-activating factor (PAF) causes hypotension, cardiac dysfunction, increased vascular permeability, intestinal necrosis, and pulmonary microvascular injury when administered experimentally. Receptor antagonism attenuates or abolishes many of these effects in animal models of bacteremia, endotoxemia, and intestinal ischemia/reperfusion (I/R). The purpose of this study was to further examine the role of PAF in intestinal I/R-induced pulmonary injury using the PAF receptor antagonist WEB 2086. Sprague-Dawley rats were anesthetized and cannulated for measurement of mean arterial pressure, heart rate, and cardiac output. Laparotomy and thoracotomy were performed and the superior mesenteric artery was occluded for 45 min and reperfused for 120 min. Sham animals were treated similarly but without I/R. In the treatment groups, iv WEB 2086 (20 mg/kg/l cc NS) was administered as a bolus 15 min prior to reperfusion. Hemodynamic and videomicroscopic data were obtained before and during ischemia, and after reperfusion at 30-min intervals. Alveolar leak index was calculated offline via computer analysis of videomicroscopic images. Intestinal I/R caused pulmonary macromolecular leakage and hemodynamic instability. Treatment with WEB 2086 attenuated the pulmonary leak during the entire reperfusion period but improved cardiac output only during the first 30 min of reperfusion and had no effect on other hemodynamic variables. These data suggest that PAF is an important, but not the exclusive, mediator of pulmonary injury after intestinal I/R. PAF appears to play a minor role in the hemodynamic derangements observed after rat intestinal I/R.     

Myocardial ischemia and reperfusion are associated with an increased stiffness of remote nonischemic myocardium

During and after an ischemic injury, maintenance and recovery of cardiac function may critically depend on remote nonischemic myocardium. Graded myocardial ischemia is associated with an approximately 50% increase in stiffness of nonischemic myocardium. We determined whether this increase in stiffness is unique to the ischemic period or persists during reperfusion. Ten anesthetized (isoflurane 1.0% vol/vol) open-chest dogs were instrumented to measure left ventricular pressure and dimensions (sonomicrometry) in ischemic and nonischemic myocardium. Regional chamber stiffness and myocardial stiffness were assessed using the end-diastolic pressure-length relationship which was modified by stepwise infusion and withdrawal of 200 mL of the animals' own blood during baseline, 45 min low flow ischemia (systolic bulge), and 60 min after the onset of reperfusion. In remote nonischemic myocardium, regional myocardial ischemia was associated with a significant (P < 0.05) increase in chamber stiffness (+44%) and myocardial stiffness (+48%). Sixty minutes after the onset of reperfusion, chamber stiffness (+54%, P < 0.05 versus baseline) and myocardial stiffness (+55%, P < 0.05 versus baseline) remained increased. Thus, the ischemia-induced increase in stiffness of remote nonischemic myocardium persists for at least 60 min after reperfusion.     

Effects of the 21-aminosteroid U-74389G on ischemia and reperfusion injury of the ascending colon in horses

Sixteen horses were allotted at random to 3 groups: vehicle only; low dosage (vehicle and 3 mg of U-74389G/kg of body weight); high dosage (vehicle and 10 mg of U-74389G/kg). These solutions were given prior to reperfusion. The ascending colon was subjected to 2 hours of ischemia followed by 2 hours of reperfusion. Before, during, and after ischemia, full-thickness colonic tissue biopsy specimens were obtained for measurement of malondealdehyde (MDA) concentration and myeloperoxidase activity and for morphologic evaluation. Although increases were not significant, MDA concentration and myeloperoxidase activity increased during ischemia and reperfusion. Administration of U-74389G did not have significant effects on MDA concentration and myeloperoxidase activity. However, the lower dosage tended (P = 0.08) to reduce myeloperoxidase activity at 30 and 60 minutes of reperfusion. In horses of the vehicle-only group, ischemia induced a decrease in mucosal surface area that was continued into the reperfusion period (P < or = 0.05). Administration of U-74389G at both dosages (3 and 10 mg/kg) prevented the reperfusion-induced reduction in mucosal surface area, which was significant at 60 minutes (high dosage; P = 0.05) and 90 minutes (low and high dosages; P = 0.02). After initial reduction in horses of all groups, mucosal volume increased for the initial 60 minutes of reperfusion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Molecular basis of type III hyperlipoproteinemia in Germany

1. The aim of the present investigation was to evaluate the effect of cloricromene on myocardial infarct size, regional myocardial blood flow and neutrophil accumulation in a canine model of ischaemia-reperfusion. 2. Dogs were instrumented to measure blood pressure, left anterior descending (LAD) coronary flow (flow probe) and regional myocardial blood flow (coloured microspheres). Two groups were studied: (i) CLO (n = 8) received an infusion of cloricromene (15 micrograms/kg per min); and (ii) VEH (n = 8) received saline. Infusions began at the onset of ischaemia (60 min) and continued through reperfusion (180 min). 3. Haemodynamic responses were not different between groups. Cloricromene reduced the area of necrosis expressed as a percentage of the area at risk from 35 +/- 3% in the VEH group to 23 +/- 4% in the CLO group (P < 0.05). Regional myocardial blood flow in the ischaemic region was different between groups; VEH dogs showed an early reperfusion hyperaemia followed by a progressive reduction in flow, while CLO dogs exhibited a gradual increase in reflow in the absence of an early hyperaemic response (P < 0.05). Left anterior descending flow was enhanced during the reperfusion period in the CLO group compared with VEH (P < 0.05). Cloricromene reduced polymorphonuclear neutrophil (PMN) infiltration (myeloperuxidase activity) in all myocardial regions when compared with VEH (non-ischaemic zone, 0.34 +/- 0.54 vs 0.05 +/- 0.01 IU/100 mg; ischaemic zone, 2.03 +/- 0.80 vs 0.24 +/- 0.08 IU/100 mg; and necrotic zone, 0.56 +/- 0.04 vs 3.59 +/- 1.09 IU/100 mg for VEH vs CLO groups, respectively; P < 0.01). In a separate in vitro preparation, cloricromene reduced adherence of platelet-activating factor (PAF)-stimulated PMN to canine coronary endothelium. Stimulation of PMN by 100 nmol/L PAF resulted in adherence of 176 +/- 36 compared with 48 +/- 12 cells/mm2 in PAF-stimulated PMN treated with 100 mumol cloricromene (P < 0.001). 4. These data indicate that cloricromene reduces myocardial infarct size in a canine model of ischaemia-reperfusion injury. Postischaemic blood flow patterns are significantly different in cloricromene-treated dogs. Cloricromene-mediated reductions in infarct size, neutrophil accumulation and adherence may play a role in this effect.     

Effect of hyperbaric oxygen therapy on testicular ischemia-reperfusion injury

PURPOSE: Testicular torsion is a urologic emergency representing a form of ischemia-reperfusion (IR) injury that requires prompt care to achieve tissue salvage and a reduction in post-torsion morbidity. Hyperbaric oxygen (HBO) has shown benefits in previous musculoskeletal models of IR. We evaluated the efficacy of HBO treatment in a rat testicular torsion model. MATERIALS AND METHODS: Four groups of male Wistar rats were included in this study: 1) Sham (n=16), spermatic cords exposed but not occluded; 2) Control (n=16), 4 hours of bilateral spermatic cord occlusion; 3) HBO during ischemia (n=18), 4 hours of occlusion and administration of HBO during the last 90 minutes of ischemia; and 4) HBO on reperfusion (n=8), HBO administered immediately upon reperfusion of the testes. The animals were sacrificed at two weeks and architecture and germinal epithelial cell thickness were determined by histological examination on each testicle. Average thickness (in cell layers) of each group was compared with control using Student's t test. RESULTS: Control testicles showed a significant reduction in germinal cell thickness compared with sham (1.7 versus 6.3, p <0.05). The animals treated with HBO during ischemia showed a significant increase in epithelial cell thickness compared with control (2.8 versus 1.7, p <0.05). Hyperbaric oxygen treatment during reperfusion had the greatest beneficial effect compared with control (5.1 versus 1.7, p <0.05). CONCLUSIONS: Adjunctive HBO therapy administered during ischemia or reperfusion significantly reduced injury to the testicle in this animal model. These results suggest a potential benefit of HBO treatment in clinical situations of testicular torsion.     

Involvement of platelet-activating factor in cell death induced under ischemia/postischemia-like conditions in an immortalized hippocampal cell line

The involvement of platelet-activating factor (PAF) in cell damage induced by ischemia/postischemia-like conditions was studied in a hippocampus-derived cell line, HN33.11. Cells exposed to N2-saturated glucose-free HEPES-buffered saline (ischemia) for 5 h followed by 18 h of incubation in serum-free control medium (postischemia reincubation) remained 67.4 +/- 2.4% viable in comparison with sham-treated cells. Analysis of DNA fragmentation in combination with Hoechst 33258 staining indicates that apoptosis is the dominant mode of cell death in the present model. PAF level during 10 h of ischemia was unchanged. However, an increase in PAF accumulation was found early during the reincubation period that followed 5 h of ischemia. Peak PAF concentrations were noted at 2 h after initiation of reincubation and rapidly declined to control level after 7 h of reincubation. Consistent with a role of PAF in mediating cell death under ischemia/postischemia reincubation in this model, the PAF antagonist BN 50739 exerted a dose-dependent protective effect. Maximal protection (85.7 +/- 5.4%) of the cells from ischemia/reincubation-induced cell damage was achieved at 0.1 microM BN 50739. The PAF antagonist lacked any protective effect against ischemia-induced cell death. On the other hand, the addition of the stable PAF analogue 1-O-hexadecyl-2-N-methylcarbamyl-sn-glycero-3-phosphocholine (MC-PAF) at the onset of ischemia potentiated ischemia/reincubation-induced apoptosis--an effect that was blocked by BN 50739. Pretreatment of HN33.11 cells with the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N,N-tetraacetic acid acetoxymethyl ester (BAPTA-AM) also provided a protective effect against ischemia/reincubation-induced cell damage. BAPTA-AM increased cell viability by 50%. Pretreatment with BAPTA-AM also decreased ischemia/reincubation-induced PAF accumulation in HN33.11 cells. The results suggest that PAF, acting via a PAF receptor, is at least in part mediating apoptosis under ischemia/postischemia-like conditions in HN33.11 cells.     

Platelet-activating factor inhibits (Na+,K+) ATPase activity in rat brain

In the present study, experiments were conducted to determine the effect of platelet-activating factor (PAF) on (Na+,K+)-ATPase in rat cerebral cortex. PAF, but not lysoPAF, inhibited (Na+,K+)ATPase activity, in a dose- and time-dependent manner, 10(-7) to 10(6) M being the most effective dose. These effects were abolished in the presence of PCA-4248, a PAF antagonist, indicating that the PAF effect may be mediated by its specific membrane receptors. Omission of external calcium caused an increase in the basal activity and abolished the PAF effect on (Na+,K+)ATPase. The present study demonstrates that PAF inhibits (Na+,K+)ATPase activity in the cerebral cortex and suggests that PAF released during certain pathological conditions, such as ischemia, may act on ATPase. This could be one possible mechanism of PAF action that needs further attention.     

Effect of pertussis toxin and B-oligomer on platelet-activating factor-induced generation of inositol phosphates in porcine alveolar macrophages

OBJECTIVE: To test the hypothesis that platelet-activating factor (PAF) induces inositol phosphate turnover through a receptor-linked, pertussis toxin-sensitive guanine nucleotide-binding (G) protein-dependent pathway in porcine alveolar macrophages. DESIGN: Randomized complete block design was used with 2 or 3 replicates/block. ANIMALS: Porcine alveolar macrophages were obtained by lavage of excised lungs from Yorkshire-type pigs (mean +/- SEM, 21 +/- 2 kg). PROCEDURE: Phospholipase C activation was assessed, using anion exchange chromatography to measure accumulation of inositol phosphates in [3H]myo-inositol-labeled alveolar macrophages. Macrophages were incubated with saline solution, pertussis toxin (4.75 nM), or B-oligomer (4.75 nM) for 2 hours. Cells then were washed and incubated for 5 minutes with PAF (0, 0.1, 1.0, or 10 microM; n = 15). Results were expressed as total inositol phosphates (inositol monophosphate, bisphosphate, trisphosphate, and tetrakisphosphate). RESULTS: Concentrations of total inositol phosphates were significantly (P < 0.05) increased to 162 +/- 7, 172 +/- 4, and 194 +/- 9% of control in response to 0.1, 1.0, and 10 microM PAF, respectively. Pertussis toxin attenuated the PAF-induced increase in total inositol phosphates by approximately 50% (P < 0.05). The B-oligomer of pertussis toxin failed to modify PAF-induced increases in total inositol phosphates. The specific PAF receptor antagonist WEB 2086 markedly attenuated PAF-induced. (10 microM) increase in inositol phosphates. CONCLUSIONS: We conclude that PAF stimulates accumulation of inositol phosphates through a specific receptor and that a pertussis toxin-sensitive G protein is involved in the signal transduction process leading to activation of phospholipase C in porcine alveolar macrophages.     

Inhalation of platelet-activating factor induced guinea pig airway hyperresponsiveness: role of eosinophils activation

Exposure of guinea pigs to aerosols of 200 micrograms/ml platelet-activating factor 24 h later, airway hyperresponsiveness to histamine induced and number of eosinophils and hypodense eosinophils in bronchoalveolar lavage fluid (BALF) increased, comparing with the control group. The number of eosinophils in BALF was corelated with PC20 value in PAF-treated group (r = -0.62, P < 0.05). However, the percentage of hypodense eosinophil in BALF had closer relation to airway responsiveness (r = -0.84, P < 0.01). The content of peroxidase in hypodense eosinophils in BALF for guinea pigs treated by inhalation of PAF was lowered markedly than that in normodense eosinophil (P < 0.05). The result suggested that chemotaxis and activation of eosinophils by PAF might play an important role in airway hyperresponsiveness.     

Effect of anesthetic methods on hemodynamics and metabolic changes caused by hepatic ischemia and reperfusion in pigs

The effects of halothane, isoflurane and epidural anesthesia combined with isoflurane on hemodynamic and metabolic changes caused by hepatic ischemia and reperfusion were studied in 16 pigs. Hepatic arterial and portal venous blood flows were measured electromagnetically. Lactate pyruvate ratio (L/P) and arterial ketone body ratio (AKBR) were calculated as markers of hepatic aerobic metabolism. Total hepatic blood flow (THBF), cardiac output (CO) and THBF/CO showed no significant differences among three anesthetic methods in ischemic and reperfusion period. In the group with epidural anesthesia combined with isoflurane, L/P was significantly lower and AKBR was significantly higher compared with the data obtained in ischemic period. However, hepatic metabolism was severely disturbed after the reperfusion of the liver in all three groups. Especially, halothane group showed the most remarkable decrease in AKBR. In summary, epidural anesthesia will be useful for aerobic hepatic metabolism because of inhibition of the release of endogenous cathecolamines, but hepatic metabolism will not be maintained following hepatic ischemia and reperfusion.     

Sequential systemic platelet-activating factor and interleukin 8 primes neutrophils in patients with trauma at risk of multiple organ failure

Plasma from 33 patients at risk of multiple organ failure (MOF) after major trauma was tested for a priming effect on neutrophils, and for the presence of platelet-activating factor (PAF) activity and interleukin (IL) 8. Plasma sampled at 3, 6, 12 and 24 h after injury significantly primed normal neutrophils to release mean(s.e.m.) 1.26(0.19), 1.33(0.26), 1.04(0.14) and 0.86(0.13) nmol superoxide per min per 1.3 x 10(6) neutrophils respectively (P < 0.05). Priming at 3 h after injury was inhibited by mean(s.e.m.) 63.8(7.0) per cent by the PAF antagonist, WEB 2170 (P < 0.01). Mean(s.e.m.) plasma IL-8 was raised at 6 and 12 h after injury to 785(183) and 836(175) pg/ml (P < 0.01). At 12 h after injury the plasma IL-8 level correlated directly with the number of units of red blood cells transfused (r = 0.64, P < 0.01), and was significantly higher in the group of six patients who developed MOF (P < 0.05). These data suggest that after trauma the mediators PAF and IL-8 appear sequentially in the circulation, are potential mechanisms of circulating neutrophil priming, and that IL-8 may also be an early biochemical marker predicting the onset of MOF.     

The effect of a free radical scavenger and platelet-activating factor antagonist on FFA accumulation in post-ischemic canine brain

The effects of the platelet-activating factor antagonist BN 50739 and a free radical scavenger dimethyl sulfoxide on the accumulation of free fatty acids in post-ischemic canine brain are reported. Following 14 min of complete normothermic ischemia and 60 min of reperfusion, the total brain FFAs were approximately 150% higher than in the control group (p < 0.05). Perfusion with the platelet-activating factor antagonist BN50739 in its diluent dimethyl sulfoxide during 60 min of post-ischemic reoxygenation resulted in a 61.8% (p < 0.01) reduction in the total brain free fatty acid accumulation. Palmitic, stearic, oleic, linoleic, and arachidonic acids decreased by 53.8%, 63.5%, 69.0%, 47.4%, and 57.2%, respectively. Although dimethyl sulfoxide alone caused stearic and arachidonic acids to return to the normal concentration range, BN 50739 had a significant influence on recovery of palmitic, oleic, and linoleic acids and was previously shown to provide significant therapeutic protection against damage to brain mitochondria following an ischemic episode. Because free fatty acid accumulation is one of the early phenomena in cerebral ischemia, this study provides evidence to support the hypothesis that both platelet-activating factor and free radicals are involved in initiating cerebral ischemic injury.     

Poststorage diastolic abnormalities of heart transplants: is vascular dysfunction or myocardial contracture the culprit?

We tested the hypothesis that mast cells contribute to platelet-activating factor (PAF)-induced airways hyperreactivity and hyperpermeability in mice. Airways reactivity to acetylcholine (ACh) and lung permeability to Evans blue (EB) dye were measured before and after PAF challenge in genetically mast cell-deficient (WBB6F1 W/Wv) and normal congenic (WBB6F1 +/+) mice, as well as mast cell-reconstituted (BMT W/Wv) mice. In addition, prostaglandin D2 (PGD2), a mast cell-specific mediator, was measured in the bronchoalveolar lavage (BAL) from +/+ and W/Wv mice to determine if lung mast cell activation was a consequence of PAF challenge. Genetically PAF-sensitive AKR/J mice were also treated with the mast cell stabilizer nedocromil prior to assessment of PAF effects on ACh reactivity. Intravenous PAF (10 micrograms/kg) induced a significant (P < 0.05) increase in airways reactivity to ACh (25 micrograms/kg) in both +/+ (371 +/- 52%) and W/Wv (122 +/- 24%) mice. There was a significantly greater increase in +/+ compared with W/Wv mice. PAF-induced hyperreactivity to ACh in BMT W/Wv mice (191 +/- 44%) was significantly (P < 0.05) greater than age-matched W/Wv mice (80 +/- 16%), but not significantly different from age-matched +/+ mice (153 +/- 44%). PAF (10 micrograms/kg) also significantly (P < 0.5) increased lung permeability in +/+ and W/Wv mice, but there was no significant difference between groups. BAL PGD2 increased significantly in +/+ mice following PAF challenge (559 +/- 24 ng/ml) compared with vehicle controls (152 +/- 8 pg/ml). There was no significant increase in BAL PGD2 from W/Wv mice. Nedocromil pretreatment significantly (P < 0.05) decreased PAF-induced hyperreactivity in AKR/J mice but not in W/Wv mice (P > 0.05). We conclude that mast cells contribute significantly to PAF-induced hyperreactivity but not hyperpermeability in mice.     

The effect of short- vs. long-term platelet-activating factor exposure on mouse preimplantation embryo development

Preimplantation mouse embryos (n = 1540) were cultured in the presence of platelet-activating factor (PAF) (10(-7)- 10(-14) mol/l) to the hatched blastocyst stage. A dose-dependent negative correlation (-0.75783) relationship between blastocysts and the concentration of PAF was statistically significantly different (p < 0.001). Long-term but not short-term PAF exposure is detrimental to preimplantation Swiss Webster mouse embryos. Short-term PAF (10(-9) mol/l) exposure was found significantly (p < 0.05) to reduce blastocoel diameter. The effect of PAF during preimplantation development may be genotype dependent and be affected by the culture conditions.     

Studies on hepatic injury and antioxidant enzyme activities in rat subcellular organelles following in vivo ischemia and reperfusion

The activities of rat hepatic subcellular antioxidant enzymes were studied during hepatic ischemia/reperfusion. Ischemia was induced for 30 min (reversible ischemia) or 60 min (irreversible ischemia). Ischemia was followed by 2 or 24 h of reperfusion. Hepatocyte peroxisomal catalase enzyme activity decreased during 60 min of ischemia and declined further during reperfusion. Peroxisomes of normal density (d = 1.225 gram/ml) were observed in control tissues. However, 60 min of ischemia also produced a second peak of catalase specific activity in subcellular fractions corresponding to newly formed low density immature peroxisomes (d = 1.12 gram/ml). The second peak was also detectable after 30 min of ischemia followed by reperfusion for 2 or 24 h. Mitochondrial and microsomal fractions responded differently. MnSOD activity in mitochondria and microsomal fractions increased significantly (p < 0.05) after 30 min of ischemia, but decreased below control values following 60 min of ischemia and remained lower during reperfusion at 2 and 24 h in both organelle fractions. Conversely, mitochondrial and microsomal glutathione peroxidase (GPx) activity increased significantly (p < 0.001) after 60 min of ischemia and was sustained during 24 h of reperfusion. In the cytosolic fraction, a significant increase in CuZnSOD activity was noted following reperfusion in animals subjected to 30 min of ischemia, but 60 min of ischemia and 24 h of reperfusion resulted in decreased CuZnSOD activity. These studies suggest that the antioxidant enzymes of various subcellular compartments respond to ischemia/reperfusion in an organelle or compartment specific manner and that the regulation of antioxidant enzyme activity in peroxisomes may differ from that in mitochondria and microsomes. The compartmentalized changes in hepatic antioxidant enzyme activity may be crucial determinant of cell survival and function during ischemia/reperfusion. Finally, a progressive decline in the level of hepatic reduced glutathione (GSH) and concomitant increase in serum glutamate pyruvate transaminase (SGPT) activity also suggest that greater tissue damage and impairment of intracellular antioxidant activity occur with longer ischemia periods, and during reperfusion.     

Epileptic seizures, epilepsy and risk factors. Experiences with an investigation in Martinique. Epimart Group

Dextrans of mean molecular weight 70 kDa (dextran-70) have had clinical use as anti-thrombotics in man. A major part of the anti-thrombotic action is mediated via inhibition of platelet function. Greatorex (1975, 1977) treated thromboembolic colic in horses with infusions of dextran-70 and reported a 90% recovery rate, but this treatment is nonetheless rarely used. We have used an in vitro method to examine the effect of dextran-70 on equine platelet suspensions, in the hope that understanding the mechanism of action of dextran-70 might lead to the development of alternative therapeutic agents. The effects of dextran-70 on equine platelets occurred immediately in vitro with an initial activation and shape change. Subsequent assessment of aggregation revealed a dose-dependent specific inhibition of platelet-activating factor (PAF)-induced aggregation, significant in rate of aggregation at dextran-70 concentrations >40 g/l (P<0.05) and in extent of aggregation at dextran-70 concentrations >50 g/l (P<0.05). Pre-incubation with 60 g/l dextran-70 significantly inhibited the rate and extent of aggregation in response to PAF (1 nmol/l) (P<0.001 and P = 0.003, respectively) but this was not dependent on the duration of pre-incubation (from 0 to 150 min). No effects were seen when the agonist was adenosine 5'-diphosphate (200 nmol/l), collagen (10 mg/l), 5-hydroxytryptamine (100 micromol/l) or U44069 (600 nmol/l) (all P>0.1). Analysis of PAF concentration-aggregation curves after pre-incubation with 60 g/l dextran-70 indicated significant noncompetitive inhibition by dextran-70 (P<0.001 for rate and extent of aggregation). The ability of dextran-70 to inhibit responses of equine platelets to PAF is probably an important component of its beneficial effect as an anti-thrombotic in colic cases.