IN VIVO EFFECTS OF CARDIOTROPHIN-1

Cardiotrophin-1 (CT-1) is a recently discovered cytokine that was isolated based on its ability to induce cardiac myocyte hypertrophy in vitro. In this study, the effects of chronic administration of CT-1 to mice (0.5 or 2 μg by intraperitoneal injection, twice a day for 14 days) were determined. A dose-dependent increase in both the heart weight and ventricular weight to body ratios was observed in the treated groups. The body weights of the animals were unaffected. These results indicate that CT-1 can induce cardiac hypertrophy in vivo. CT-1 was not specific for the heart, however. It stimulated the growth of the liver, kidney, and spleen, and caused atrophy of the thymus. CT-1 administration also increased the platelet counts by 70%, with no change in mean platelet volume. Red blood cell counts were increased in the treated animals, and there was a concomitant increase in haemoglobin concentration. Thus, CT-1 has a broad spectrum of biological activities in vivo. This observation is consistent with previous in-vitro findings showing that the mRNA for CT-1 is expressed in several tissues, and that CT-1 can function through binding to the leukaemia inhibitory factor (LIF) receptor and signalling through the gp130 pathway.     

Incomplete cerebral ischemia in the rat provokes increase of tissue and plasma malondialdehyde

Short-term incomplete cerebral ischemia was induced in the rat by bilaterally clamping for 5 min the common carotid arteries; subsequent reperfusion of 10 min was obtained by removing carotid occlusion. At the end of ischemia or reperfusion, animals were sacrificed by decapitation. A control group was represented by sham-operated rats. Peripheral venous blood samples were withdrawn from the femoral vein from rats subjected to cerebral reperfusion 5 min before ischemia, at the end of ischemia, and 10 min after reperfusion. A highly sensitive HPLC method for the direct determination of malondialdehyde, oxypurines, and nucleosides was used on 200 μL of brain tissue and plasma extracts. Incomplete cerebral ischemia induced the, appearance of a significant amout of tissue malondialdehyde (undetectable in control animals) and a decrease of ascorbic acid. A further 6.6-fold increase of malondialdehyde and a 18.5% decrease of ascorbic acid occurred after 10 min of reperfusion. Plasma malondialdehyde, which was present in minimal amount before ischemia, significantly increased after 5 min of ischemia, being strikingly augmented after 10 min of reperfusion. A similar trend was observed for oxypurines and nucleosides. From these data, it can be affirmed that tissue concentrations of malondialdehyde and ascorbic acid, and plasma levels of malondialdehyde, oxypurines, and nucleosides, reflect both the oxygen radical-mediated tissue injury and the depression of energy metabolism thus representing early biochemical markers of short-term incomplete brain ischemia, and reperfusion in the rat.     

Pathological changes of myocardial cytoskeleton in cardiomyopathic hamster

Immunocytochemical investigation was performed on the cytoskeletal proteins in cardiac tissue of the cardiomyopathic hamster. Male cardiomyopathic UM-X7.1 hamsters at 180 days of age (n=8) and age- and sex-matched normal BIO-RB hamsters (n=8) were used in this study. Immunofluorescence microscopy using monoclonal antibodies against desmin, -actinin, titin, and vincullin was employed. The heart weight to body weight ratio was significantly increased in the heart of cardiomyopathic hamster compared with that of normal hamster. In cardiomyopathic hamster, the left ventricular cavity was markedly dilated. Light microscopically, hypertrophy and atrophy of myocytes and myocardial fibrosis were prominently observed in cardiomyopathic myocardium. Immunocytochemically, desmin, -actinin and titin showed the cross striations along the myofibers in normal myocardium. In contrast, in cardiomyopathic myocardium, desmin was irregularly distributed in myocytes and the amount of desmin was increased. Loss of cross striations of -actinin and titin were frequently observed. Immunofluorescence against vinculin was not significantly altered. We conclude that the alterations of cytoskeletal proteins in myocardial cells may relate to decreased myocardial function in cardiomyopathic hamster failing heart.     

The role of catecholamines on intercellular coupling,myocardial cell synchronization and self ventricular defibrillation

Ventricular fibrillation (VF) is one of the most life threatening events. Although in humans VF is generally sustained (SVF) requiring artificial defibrillation, in various mammals and in some cases in humans VF terminates by itself, reverting spontaneously into sinus rhythm. Since VF is one of the main causes of sudden death, one of the important clinical problems today is if and how we can transform the fatal SVF into a self limited transient one (TVF).From electrophysiological studies carried out on anaesthetized open chest animals, we have found that TVF requires a high degree of intercellular coupling and synchronization.Cardiac myocytes are electrically coupled with adjacent cells. The intercellular coupling is a focus of low electrical resistance which allows rapid transmission of electrical impulses between cells. Any decrease in intercellular coupling decreases the ability of the heart for self defibrillation. The cell-to-cell coupling decreases with age, ischemia, VF and variations in physiological conditions probably due to an increase in intercellular resistance (Ri), widening in the internexal gaps, decrease in electrotonic space constant () etc. All of these factors are known to be affected by intracellular concentration of free Ca⁺⁺ ([Ca⁺⁺]).On the basis of studies carried out on various mammals at different ages, we hypothesized that the ability of the heart to defibrillate depends on the cardiac catecholamine level [CA], during VF. This hypothesis is supported by the facts, known from the literature, that increase in [CA] decreases intracellular free Ca⁺⁺ concentration, decreases Ri and increases . By these effects, increase in [CA] enhances intercellular coupling and intercellular synchronization, and thereby, according to our hypothesis, leads to spontaneous ventricular defibrillation — TVF.During VF the sympathetic activity is enhanced but in some cases the [CA] does not reach the level needed for TVF. In order to help the heart in its effort to elevate the [CA] during VF, we proposed to treat these cases with drugs which inhibit the reuptake of [CA]. The facts that administration of [CA] reuptake inhibitors, before the induction of VF, and/or intracoronary infusion of adrenaline, during VF, transforms SVF into TVF, emphasized the validity of our hypothesis.     

Transient Ischemia Differentially Increases Tyrosine Phosphorylation of NMDA Receptor Subunits 2A and 2B

Abstract: Activation of the N -methyl- d -aspartate (NMDA) receptor has been implicated in the events leading to ischemia-induced neuronal cell death. Recent studies have indicated that the properties of the NMDA receptor channel may be regulated by tyrosine phosphorylation. We have therefore examined the effects of transient cerebral ischemia on the tyrosine phosphorylation of NMDA receptor subunits NR2A and NR2B in different regions of the rat brain. Transient (15 min) global ischemia was produced by the four-vessel occlusion procedure. The tyrosine phosphorylation of NR2A and NR2B subunits was examined by immunoprecipitation with anti-tyrosine phosphate antibodies followed by immunoblotting with antibodies specific for NR2A or NR2B, and by immunoprecipitation with subunit-specific antibodies followed by immunoblotting with anti-phosphotyrosine antibodies. Transient ischemia followed by reperfusion induced large (23–29-fold relative to sham-operated controls), rapid (within 15 min of reperfusion), and sustained (for at least 24 h) increases in the tyrosine phosphorylation of NR2A and smaller increases in that of NR2B in the hippocampus. Ischemia-induced tyrosine phosphorylation of NR2 subunits in the hippocampus was higher than that of cortical and striatal NR2 subunits. The enhanced tyrosine phosphorylation of NR2A or NR2B may contribute to alterations in NMDA receptor function or in signaling pathways in the postischemic brain and may be related to pathogenic events leading to neuronal death.     

Characterisation and serological relationships of strains of Kashmir bee virus

Isolates of novel strains of Kashmir bee virus (KBV) were obtained from field-collected dead adults of Apis mellifera from honey bee colonies in Canada and Spain. They differed from other strains of KBV in their tendency to aggregate in dilute buffer solution and in containing only three proteins when analysed by SDS-polyacrylamide gel electrophoresis compared with five proteins resolved in the type strain of KBV from Apis cerana in India and six proteins in KBV strains from South Australia and New Zealand. Immunodiffusion tests and Western blotting studies indicated that the five virus isolates were serologically related and all were related to acute paralysis virus (APV). The world distribution of KBV strains and their apparent relationship with APV are discussed.     

Prevalence and upper limit of cardiac hypertrophy in professional cyclists

The term athlete's heart refers to an increased left ventricular mass. Few studies have assessed the prevalence and normal upper limit of cardiac hypertrophy in highly trained cyclists and this was the aim of this study. A group of 40 professional road cyclists [mean age 26 (SD 3) years] who had participated in European competitions for 3–10 years, were evaluated at the beginning of the 1992–93 season. Evaluation included a clinical history and physical examination, one and two-dimensional echocardiography, 12-lead resting electrocardiogram and a graded exercise test. Determination of the left ventricular mass index (LVMI) was performed using Devereux's formula with correction for the body surface area. Systolic and diastolic blood pressure were measured at rest and at peak exercise. Of the group 23 cyclists (58%) presented a LVMI greater than 130 g · m^–2, 21 cyclists presented a diastolic ventricular thickness equal to or greater than 13 mm, with a superior limit of 19 mm; 3 cyclists presented asymmetrical septum hypertrophy; and the relationship between posterior wall and left ventricular diastolic radius was equal to or greater than 0.45 in 14 cases (35%). Electrocardiographic abnormalities of ST-T segment were seen in only 1 subject. No correlation was found between the degree of ventricular hypertrophy and arterial blood pressure. We concluded that these professional cyclists showed a high prevalence of cardiac hypertrophy (58%). The distribution of this hypertrophy was concentric in 20/33 and asymmetric in 3/23 of the subjects with left ventricular hypertrophy. The electrocardiograms were normal in 98% of the subjects.     

Baclofen is cytoprotective to cerebral ischemia in gerbils

The release of the neurotransmitter, glutamate, and the activation of receptor operated calcium channels, may increase the degree of damage in ischemic brain tissue. Inhibition of excitatory neurotransmitters should therefore result in cytoprotection of ischemic brain tissue. In this study we evaluated the effect of baclofen, an inhibitor of presynaptic glutamate release, on ischemic gerbil cortex, hippocampus (CA 1 and CA4), striatum and thalamus. Histological evaluation was done in a blind manner in 4 groups (total 36 animals): a control group (9 animals) and three groups (27 animals) with varying doses of baclofen. For cerebral ischemia, we used single episode of five minutes of arterial occlusion of the carotid arteries. Baclofen in doses of 0, 25, 50, and 100 mg/kg were given to different groups five minutes prior to ischemic insult. This was followed by intraperitoneal injections given 24 and 48 hours after the initial insult. Statistically significant histological cytoprotection was demonstrated. Doses of 25 mg/kg appeared to demonstrate significant protection of the cortex (p=0.0002), the CA1 and CA4 regions of the hippocampus (p=0.0004 and 0.0001) respectively. At a dose of 50 mg/kg, significant cytoprotection was demonstrated at the hippocampus (CA1 and CA4 regions), in particular at the CA4 region (p=0.0029). The 100 mg/kg dose appeared to have most significant protection at the CA1 and CA4 regions of the hippocampus (both p=0.0001), striatum (p=0.0011), and the thalamus (p=0.0008). All statistical comparisons were done using non-parametric tests (Mann-Whitney U test). Our study demonstrates that baclofen is cytoprotective to ischemic neuronal cells, especially in the hippocampus. Clinically this may be beneficial to those patients with strokes or head injuries.     

GABA concentrations in the striatum following repetitive cerebral ischemia

GABAergic neurons in the striatum are very sensitive to the effects of ischemia. The progressive decline in striatal GABA following transient forebrain ischemia in gerbils may be secondary to either a decreased production or an increase in reuptake mechanisms or both. The current experiment was designed to evaluate release of GABA by stimulation with K+ or inhibition of its uptake with nipecotic acid or their combination (K+ nipecotic) after repetitive forebrain ischemia in gerbils by in-vivo microdialysis on Days 1, 3, 5, and 14 following the insult. Infusion of nipecotic acid or potassium chloride, resulted in a significant increase in extracellular GABA. This response was significantly decreased in the post-ischemic animals. The synergistic effect of increased GABA concentrations by the infusion of nipecotic acid+potassium chloride seen in the controls was not evident in the post-ischemic animals. In conclusion, though there is a reduction in the extracellular GABA concentrations in the first week following an ischemic insult, restorative mechanisms are operative in the second week as seen by the increasing GABA concentrations.