Biomedical subjects

M Borgers

Publications and source records attributed to M Borgers.

At least 19 recordsLinked to original sources

PubMed1992

Synaptic plasticity in rat hippocampus associated with learning.

Rats subjected to a one-way active avoidance task consisting of 3 daily training sessions, showed obvious shape changes in dendritic spines of the hippocampal supragranular molecular layer. Performance, expressed as the number of avoidances per 10 trials, significantly improved in the second and third session (P < 0.001). In trained animals, at the end of the third session, the amount of perforated concave synapses significantly increased as compared to untrained controls (P < 0.05). When compared with a group of sham-shocked rats, the increase was less pronounced. The length of the postsynaptic density in both, perforated and non-perforated synapses, significantly increased in comparison with untrained control and sham-shocked animals (perforated: P < 0.005; non-perforated: P < 0.05). The results are indicative for the existence of synaptic remodeling and turnover in rats subjected to one-way active avoidance training.

Animals↗

PubMed1992

Protection of human, rat, and guinea-pig atrial muscle by mioflazine, lidoflazine, and verapamil against the destructive effects of high concentrations of Ca2+.

In right atrial trabeculae from humans and in left atria from rat and guinea-pig hearts, the protective effects of mioflazine, lidoflazine, and verapamil against the accumulation of cellular calcium were investigated. Two consecutive, cumulative increases in the extracellular calcium concentration, [Ca2+]o (1-25 mmol/l), were induced, in between which the muscles were exposed for at least 30 minutes to solvent or drug. When using solvent in the 30-minute interval, the force of contraction was much lower during the second Ca2+ challenge, while the aftercontractions and the increase in passive tension at high [Ca2+]o tended to be larger. These signs of functional impairment were prevented by exposure to mioflazine or lidoflazine (3 mumol/l each) but not to verapamil (3 mumol/l). Muscles were fixed with glutaraldehyde at the end of the second Ca2+ challenge for morphological and cytochemical examination. After solvent treatment, more than half of the cells were severely damaged, showing cellular edema, contraction-band necrosis, mitochondrial swelling, and nuclear pyknosis; the sarcolemma was devoid of calcium deposits, damaged mitochondria contained either large deposits of calcium or flocculent densities, and in some cells, the cytoplasm was filled with calcium deposits. Following exposure to mioflazine and lidoflazine, but not to verapamil, the number of intact cells after the second Ca2+ challenge was not different from time-matched controls (80-90%). Furthermore, the shifts in cellular calcium distribution were prevented with mioflazine and lidoflazine, whereas verapamil was less effective. There were no species differences with respect to either morphological or contractile changes. In conclusion, exposure of atria to high [Ca2+]o induced similar ultrastructural and cytochemical changes as seen after ischemia-reperfusion induced damage. Indeed, under the mentioned conditions the sarcolemma lost its capacity to exclude Ca2+ after a challenge with high [Ca2+]o and allowed excessive Ca2+ entry. The pathway for this extra Ca2+ remains to be elucidated. L-type calcium channels are probably not involved, since verapamil cannot prevent the Ca2+ overload.

Animals↗

PubMed1992

Microwave-enhanced silver staining of degenerating neuronal processes.

A simple and rapid method for light and electron microscopic visualization of degenerating neuronal processes and axon terminals is described. Hundred-micrometer vibratome sections of perfusion-fixed rat brain were incubated briefly in a 5% silver nitrate solution in a conventional microwave oven. After a rinse in 1% acetic acid, the sections were silver enhanced. Differentiation and counterstaining was done respectively in ethanol 100% and cresyl violet. In the light microscope, degenerating neuronal processes appeared as black dots against a clear background. Areas of calcification were also positively stained. The presence of silver deposits in degenerating presynaptic terminals and dendrites was confirmed ultrastructurally.

Animals↗

PubMed1992

Species differences in adenosine metabolic sites in the heart.

5'-Nucleotidase and purine nucleoside phosphorylase, two key enzymes in nucleoside metabolism, have been localized electronmicroscopically in left ventricular myocardium of the human, dog, pig, rabbit, guinea pig and rat. Ectonucleotidase activity was present in all species at the plasma membrane of pericytes. Reactive endothelial cells in the microcirculatory bed were restricted to those covering resistance arterioles. Cardiomyocytes were reactive only in the rat. Purine nucleoside phosphorylase was localized uniformly in the vascular endothelium of all species. The strongest activity was seen in the pericytes of guinea pig, rat and dog. Pericytes of rabbit and pig were virtually unreactive, whereas a minority of cells in human samples were positive. Cardiomyocytes were unreactive in all species. These variations in the distribution pattern of adenosine metabolic sites may have definite consequences for disposal and recovery of adenylates and their breakdown products in ischaemia and for the effects to be expected from interference with nucleoside transport inhibition.

5'-Nucleotidase↗

PubMed1992

The course of vasospasm following subarachnoid haemorrhage in rats. A vertebrobasilar angiographic study.

The course of vasospasm following subarachnoid haemorrhage in rats was studied using vertebrobasilar angiography. Wistar and Sprague Dawley rats were compared with respect to vasospastic response after bleeding. A more pronounced vasospasm was found in Sprague Dawley rats. In order to avoid a possible toxic effect on the contrast medium, only one angiogram per animal was initially performed. However, a comparison with the results obtained in a separate series of non-challenged animals demonstrated a difficulty due to high variability in basilar artery size in the latter group. Therefore, vasospasm can be more readily shown if multiple angiograms are used in the same animal so that the vasospasm can be expressed as a percentage of the initial diameter of the basilar artery. It was found that multiple angiograms are well tolerated when non-ionic contrast media are used.

Animals↗

PubMed1992

Haemodynamic, intracranial pressure and electrocardiographic changes following subarachnoid haemorrhage in rats.

Experimental induction of subarachnoid haemorrhage in rats resulted in acute haemodynamic changes. Heart rate decreased concomitantly with a rise in arterial blood pressure. Intracranial pressure increased and consequently cerebral perfusion pressure dropped. These changes as well as the observed electrocardiographic (ECG) changes were comparable to those reported in patients. Apart from blood also saline, when introduced into the cisterna magna, was able to elicit such abnormalities. The haemodynamic and electrocardiographic changes, which result from subarachnoid haemorrhage, may even become aggravated, when repetitive injections of blood or saline are given into the cisterna magna and when cerebral angiography is performed prior to induction of the subarachnoid haemorrhage. Chronic intracranial pressure monitoring during the 48 hours following subarachnoid haemorrhage revealed no significant rise in pressure. A thorough control of the experimental conditions is thus of utmost importance in order to give a valid interpretation of the observed anomalies.

Animals↗

PubMed1992

Lysophosphatidylcholine-induced Ca(2+)-overload in isolated cardiomyocytes and effect of cytoprotective drugs.

It has been previously demonstrated that lysophosphatides accumulate rapidly in ischaemic tissue, and may play a key role in the genesis of ischaemia-reperfusion injury. The present study investigated the effects of exogenously added lysophosphatidylcholine (1-20 microM) on single isolated cardiomyocytes from adult rabbit hearts. Quiescent cells exposed to > or = 8 microM lysophosphatidylcholine dose-dependently displayed irreversible hypercontraction, whereas after 60 min at 3 microM lysophosphatidylcholine, most cells remained rod-shaped (87.2 +/- 2.0%, mean +/- S.E.M.). However, when combined with electrical field stimulation (1 Hz), exposure to 3 microM lysophosphatidylcholine resulted in irreversible hypercontracture of most cells after 60 min: only 27.5 +/- 7.5% of the cells remained rod-shaped. Contracture depended upon the presence of extracellular Ca2+, and coincided with a significant rise in the median intracellular free Ca2+ level from 72.2 to 352.1 nM (P = 0.0001), suggesting intracellular Ca(2+)-overload. Pretreatment with 10(-6) M flunarizine or R 56865 significantly reduced the fraction of damaged cells when exposed to 3 microM lysophosphatidylcholine and electrical stimulation: 78.3 +/- 12.2% and 56.3 +/- 13.1% respectively of the cells remained rod-shaped. No protection was observed when quiescent cells were exposed to 10 microM lysophosphatidylcholine. Cytochemical localization of Ca2+ showed that lysophosphatidylcholine induced a loss of sarcolemma-bound Ca2+ precipitate and an accumulation of Ca2+ clusters in mitochondria of damaged cells in a dose and time dependent way. These results suggest that lysophosphatidylcholine induces functional and structural damage (Ca(2+)-overload) in isolated cardiomyocytes and that this can be prevented by cytoprotective drugs.

Animals↗

PubMed1992

Developmental changes in tolerance to ischaemia in the rabbit heart: disparity between interpretations of structural, enzymatic and functional indices of injury.

The vulnerability of the heart to injury during ischaemia and reperfusion and its responsiveness to various protective and pharmacological interventions are age-dependent. Using three independent indices of tissue injury (cardiac structure, contractile function and creatine kinase leakage), we compared the response of adult (60-90 days old) and neonatal (7 days old) isolated perfused rabbit hearts to global ischaemia and reperfusion. Prior to ischaemia, heart rate was significantly higher in neonatal hearts, as were control values for coronary flow, aortic flow and cardiac output when expressed on a dry wt basis. In experiments in which adult and neonatal hearts (n = 8 per group) were subjected to 2 min of cardioplegia and 45 min of ischaemia, the post-ischaemic recovery of all indices of cardiac function (when expressed as a percentage of pre-ischaemic control) was significantly higher in neonatal than in adult hearts. Thus, cardiac output recovered to 82.9 +/- 3.6% in the neonate but to only 57.9 +/- 6.7% in the adult (P < 0.05). The functional evidence of a greater resistance to ischaemia in the neonate was, however, contradicted by the levels of creatine kinase leakage which tended to be greater in the neonatal than in the adult heart (32.0 +/- 4.7 vs 20.0 +/- 3.1 IU/15 min/g dry wt). Morphological studies indicated that injury was comparable (moderate-to-severe in degree) in both groups. To assess further the relationship between the three indices, additional experiments were undertaken in which the duration of ischaemia in the neonate was extended to 60 min so that the post-ischaemic recovery of function was reduced to a level similar to that seen in the adult after 45 min of ischaemia. Under these conditions cardiac output recovered to 55.6 +/- 4.8% in the neonatal heart (P = NS when compared with the adult) and creatine kinase leakage increased to 88.2 +/- 13.9 IU/15 min/g dry wt--a value over four times greater than that measured in adult hearts with a comparable degree of functional injury. Morphological examination of tissue obtained after 15 min of reperfusion revealed a remarkable recovery of structure in both age groups. In conclusion, in functional terms the neonatal heart was more resistant to ischaemia than the adult; enzymic leakage, however, indicated the opposite and structural assessment revealed no differences. Thus, in comparing injury during ischaemia and reperfusion between different age groups, it is clearly important to employ several independent indices.

Age Factors↗

PubMed1992

Effects of itraconazole on phagocytosis and killing of Candida glabrata by polymorphonuclear leucocytes from guinea pigs.

Itraconazole, a systemically active antifungal, was tested for its effects on microscopically assessed phagocytosis and killing of Candida glabrata 233 in vitro. Yeast cells were exposed to itraconazole in culture and guinea-pig peritoneal polymorphonuclear leucocytes were exposed to the drug injected intraperitoneally in vivo. At a concentration of 10(-7) M and with exposure times of 1 h, itraconazole pre-treatment of the leucocytes had no effect on the ability of PMNL to ingest or kill C. glabrata. However, pre-treatment of the growing C. glabrata cells under the same conditions significantly increased their vulnerability to both phagocytosis and intracellular killing. Longer exposures of the yeasts to itraconazole further increased their susceptibility to leucocyte phagocytosis, and it also rendered the cells vulnerable to killing merely by immersion in sodium deoxycholate solution. These findings indicate that short exposures of C. glabrata to low itraconazole concentrations damages the cells sublethally and renders them highly susceptible to leucocyte killing. Itraconazole had no direct effects on leucocyte function itself.

Animals↗

PubMed1991

Protective effects of R 56 865 against ischemic damage in the isolated rabbit heart.

We examined the role of calcium in the pathogenesis of ischemic cardiac cell death in the isolated working rabbit heart subjected to normothermic global ischemia followed by reperfusion. Apart from measurements of cardiodynamic function and ultrastructural examination, we also used a cytochemical procedure to localize exchangeable calcium pools at the ultrastructural level. The effects of verapamil (1.5 x 10(-8) M, 3 x 10(-8) M) (high affinity for L-type calcium channels) were compared with those of R 56 865 (4 x 10(-7) M) (Ca2+ overload blocker with low affinity for the L-type calcium channels). A severe depression of cardiac function was observed after solvent or verapamil pretreatment and 25 min of ischemia followed by reperfusion. R 56 865 treatment resulted in a significantly improved postischemic recovery when compared to solvent and verapamil treatment groups. The ultrastructural and cytochemical results corroborated the hemodynamic findings. In solvent and verapamil-treated hearts, irreversible damage was observed mainly in mid- and endocardial areas. Ultrastructural changes were accompanied by shifts in calcium localization: i.e. loss of sarcolemmal calcium binding capacity, accumulation of calcium precipitate in the mitochondria. In the R 56 865 treatment group, damage was limited to some cells scattered in the midcardial areas. In conclusion, R 56 865, which has little affinity for the slow channels was highly effective in protecting against ischemic damage, indicating that, in this experimental set-up, the calcium responsible for cellular Ca2+ overload is not entering via L-type calcium channels.

Animals↗

PubMed1991

Functional and structural impairment in human, rat and guinea-pig atrial muscle in response to in vitro calcium overload: a cytochemical study on cellular calcium distribution.

Critical accumulation of cellular calcium in ischaemic myocardium is involved in irreversible cell damage. In human right atrial trabeculae and in rat and guinea-pig left atria, we investigated whether direct calcium overload by increasing the extracellular calcium concentration, [Ca2+]o, leads to similar impairment of function and ultrastructure as observed after ischaemia. The force of contraction was measured during two consecutive cumulative increases in [Ca2+]o (1-25 mmol/l) separated by 30 min of incubation at low [Ca2+]o. Compared to the first Ca2+ challenge, the positive inotropic effect of increasing [Ca2+]o was depressed during the second one and the after-contractions, and the increase in resting tension developing with high [Ca2+]o tended to be larger. The ultrastructure of the tissue fixed immediately after excision was well preserved. When fixed after the second Ca2+ challenge, half of the cells were severely damaged with various signs of cellular Ca2+ overload similar to those observed after ischaemic damage: the sarcolemma lost its Ca(2+)-binding properties, sarcomeres showed contraction band necrosis, the mitochondria had disrupted cristae and contained either large clusters of Ca2+ precipitate or amorphous densities (Jennings granules). In many cells, calcium precipitates were present in the cytoplasm. The morphological and functional changes were similar in the three species studied. Our results suggest that the deterioration of atrial myocardium after challenge with high [Ca2+]o or after severe ischaemia may be traced back to a common mechanism, i.e. the sarcolemma loses its competence as a permeable barrier for Ca2+ and therefore facilitates excessive Ca2+ entry. However, for the direct demonstration of calcium precipitates as a sign of cytosolic Ca2+ overload, high [Ca2+]o are required with are not normally present in the myocardium.

Animals↗

PubMed1991

Pharmacological studies of arrhythmias induced by rose bengal photoactivation.

Singlet oxygen and superoxide production by rose bengal photoactivation leads to rapid electrophysiological changes and arrhythmias. To investigate which intermediate is causative and to probe possible mechanisms, hearts (n = at least 6/group) were perfused aerobically for 10 min without rose bengal followed by 5 min with rose bengal before illumination for 20 min. In controls, all or most hearts exhibited ventricular premature beats, ventricular tachycardia, and complete atrioventricular block. Most antioxidants tested had no protective effect; histidine, however, significantly delayed the onset of electrocardiographic (ECG) changes. In further studies, two antiarrhythmic agents (quinidine and verapamil) had no little protective effect, whereas R56865 significantly delayed the onset of ECG changes and reduced the incidence of arrhythmias. However, spectrophotometric and laser pulse radiolysis studies showed that this apparent protective effect might have resulted from an interaction between R56865 and the rose bengal molecule, leading to a reduction in singlet oxygen production. In conclusion, the electrophysiological changes induced by rose bengal photoactivation are likely to be due to singlet oxygen; antiarrhythmic drugs appear to be unable to protect against the injury unless there is some interaction with the photoactivation process.

Animals↗

PubMed1991

Evaluation of factors influencing myocardial infarct size in unconscious dogs.

STUDY OBJECTIVE: The aim was to evaluate the factors determining myocardial infarct size in unconscious dogs. DESIGN: In anaesthetised open chest dogs, the left anterior descending coronary artery was occluded either by ligation or by thrombosis for different time periods (1.5 h, 4 h, 24 h), with or without reperfusion. Haemodynamic variables were recorded throughout the experiment. Radioactive microspheres (15 microns) were injected at the end of the ischaemic period to measure regional myocardial blood flow. Infarct size and area at risk were determined by the Evans blue triphenyltetrazolium staining technique followed by planimetry. SUBJECTS: Mongrel dogs of either sex (n = 16-42 per experiment), weight 18-25 kg, were used. MEASUREMENTS AND MAIN RESULTS: A large interindividual variability in infarct size was observed after occlusion of the left anterior descending coronary artery at a standardised location for a well defined period. An examination of the factors responsible for this variability was carried out in order to develop a statistical model which would make it possible to predict infarct size. Using multiple regression analysis, it was found that in most protocols (except 90 min thrombosis) more than 85% of the variability in infarct size could be explained by the size of the area at risk and the amount of collateral flow. Thus, knowing the area at risk and the collateral flow, a fairly accurate prediction can be made of the size of the infarct that the dog will develop after a defined occlusion period. Furthermore, it was found that the infarct size increased with duration of occlusion, while duration of reperfusion had no effect. In the 90 min occlusion group thrombosis induced a larger final infarct than ligature. CONCLUSIONS: A correction for baseline variables is necessary in order to compare infarct size between experimental groups. The usefulness of this procedure is shown by an example of an experimental intervention, i.e., R 56,865, a drug with known cardioprotective effects.

Animals↗

PubMed1991

Effects of R 56,865, a preventer of cellular calcium overload, on left ventricular diastolic properties during pacing-induced ischemia in dogs.

The effects of R 56,865, a compound with unusual calcium antagonistic properties, on altered left ventricular (LV) diastolic properties were studied during pacing-induced ischemia in dogs with coronary stenosis. Severe coronary artery stenosis was produced on both the left anterior descending (LAD) and circumflex (Cx) coronary arteries in anesthetized beta-blocked dogs. The right atrium was paced at 200 beats/min for 3 min. In the post-pacing period and before drug intervention, the most characteristic observation was a significant increase in LV end-diastolic pressure (LVEDP) and in the time constant of (tau) LV pressure decrease; after return of LV hemodynamics to baseline values (15 min), R 56,865 (0.16 mg.kg-1) or solvent (control) was injected and four subsequent pacing runs were performed at 30-min intervals. In the postpacing period of these four subsequent runs, there was a steep increase in LVEDP and tau-values while HR returned more slowly to baseline values. After R 56,865 infusion, the increase in LVEDP and tau-values was significantly lower than in the pretreatment run and all LVEDP values were significantly lower than in the control group. We conclude that R 56,865 effectively attenuates ischemia-induced changes in LV diastolic stiffness.

Animals↗

PubMed1991

Nebivolol increases survival in cardiomyopathic hamsters with congestive heart failure.

The genetically inbred cardiomyopathic Syrian hamster provides a valuable model of congestive cardiomyopathy: myocytolytic necrosis at 30-50 days of age is followed by cardiac hypertrophy at 150-250 days, and finally by congestive failure and death at 250-350 days. Successful drug treatment has been reported in the prenecrotic stage, but not when started during congestive failure. The present study evaluated survival of the cardiomyopathic hamster treated with the new beta-adrenoceptor blocker nebivolol, which was initiated during congestive failure. Fifty animals (BIO82.62, either sex, age 200 days) were acclimated to an environmentally controlled room for 20 days, receiving food and water ad libitum; seven hamsters died, indicating development of congestive failure. The remaining animals were then randomly assigned to one of three groups: 15 animals received control food; food for the others was supplemented with nebivolol, yielding a daily intake of either 0.1 mg/kg (n = 14) or 1 mg/kg (n = 14). At the lower nebivolol dose, death rate was unaltered in comparison with controls. However, at 1 mg/kg, survival was markedly improved (p = 0.042). Nebivolol treatment, started during congestive failure, thus significantly delays mortality in the cardiomyopathic hamster.

Adrenergic beta-Antagonists↗

PubMed1991

Myocardial protection by R 56865: a new principle based on prevention of ion channel pathology.

Intracellular Ca2+ overload is considered to be the final pathway leading to cell death under pathological conditions. However, both the route of Ca2+ entry and the site of action of cardioprotective drugs remain obscure. This was investigated using isolated adult rat and rabbit cardiomyocytes exposed to the experimental pathological stimuli veratridine, singlet O2, lysophosphatidylcholine, and ouabain. Under these conditions, the majority of cells displayed irreversible hypercontraction as a consequence of intracellular Ca2+ overload. Nifedipine did not prevent Ca2+ overload, but tetrodotoxin (TTX) and reduction of the extracellular Na+ concentration protected against the above pathological stimuli. This strongly suggests that intracellular Ca2+ overload after exposure to these pathological stimuli may be mediated via fast Na+ channel dysfunction, causing excessive entry of Na+, followed by Ca2+ overload via Na(+)-Ca2+ exchange. The new cardioprotective drug R 56865 dose dependently prevented hypercontracture induced by each of these stimuli, suggesting that R 56865 may interfere with this modified Na+ channel that is in a way different from class I antiarrhythmic drugs. This is regarded as a new cardiac cytoprotective principle.

Animals↗

PubMed1991

Stunned myocardium has increased mitochondrial NADH oxidase and ATPase activities.

Ten anesthetized, open-chest dogs were subjected to occlusion of the left anterior descending coronary artery for 15 minutes, followed by reperfusion for 150 minutes. Hemodynamics were recorded and regional myocardial contraction was measured sonometrically. The hearts were then fixed in situ using glutaraldehyde for cytochemical studies. Systolic wall thickening remained unchanged in the non-ischemic myocardium, but was significantly depressed (stunned) in the area of the left anterior descending coronary artery during reperfusion. NADH oxidase and ATPase activities were very weakly present in mitochondria from non-ischemic myocardium. In the ischemic endocardium, irreversibly injured cells had mitochondria which were severely altered and contained no reaction products to the two enzymes. In contrast, high NADH oxidase and ATPase activities were present in mitochondria from the less severely injured cells of the endocardial zone of stunned areas. Since this zone is particularly susceptible to ischemia in dogs, the high mitochondrial NADH oxidase and ATPase activities may be early signs of ischemic damage, reflecting a disturbance in mitochondrial respiratory activity in stunned myocardium.

Adenosine Triphosphatases↗

PubMed1979

Some observations on the phosphatase cytochemistry of the submandibular gland of cat.

The localization of reaction product arising from incubation with thiamine pyrophosphate at pH 7.2 and beta-glycerophosphate or nitrophenylphosphate at pH 5 has been examined in central and demilunar acinar cells, myoepithelial cells, and cells of the striated ducts. Thiamine pyrophosphate reaction product was seen in the inner saccules of the Golgi apparatuses of the different types of cell. beta-Glycerophosphate and nitrophenylphosphate reaction products were seen in lysosomes, and in GERL-like structures in all except the cells of the striated ducts, in which the reaction products were observed in the Golgi apparatus. In central cells, the latter two reactions products were also seen in secretory granules and the cytosol.

Animals↗