Carlo Hermans

Mitochondrial hydrogen peroxide generation by NADH-oxidase activity following regional myocardial ischemia in the dog.

Recently, an exogenous NADH-oxidase has been shown to be a source of oxygen derived toxic species in heart mitochondria. This enzyme uses NADH and oxygen to form superoxide radicals and hydrogen peroxide. Growing evidence suggests that oxygen radicals and hydrogen peroxide may contribute to cardiac damage during ischemia or hypoxia. The activity of the enzyme NADH-oxidase could play an important role in the damage caused by oxygen derived toxic species, especially since cellular defense mechanisms against free radicals are depleted under ischemic conditions. In this study, a cytochemical method was used to visualize hydrogen peroxide, the reaction product of NADH-oxidase activity, in normal and ischemic dog myocardium. The NADH-oxidase reaction product was present in weak amounts in mitochondria from normoxic myocardium. In viable ischemic areas a high degree of activity was observed in the mitochondria. In infarcted tissue mitochondria contained few or no reaction product at all. The results support the hypothesis that hydrogen peroxide and oxygen radicals produced in the mitochondria by a high NADH-oxidase activity may contribute to the mitochondrial damage observed during ischemia when NADH is no longer oxidized by the respiratory chain and cellular defense mechanisms are impaired.

Protective effects of etomidate in hypoxic-ischemic brain damage in the rat. A morphologic assessment

Abstract Cerebral damage was induced in rats by intermittent exposure to pure nitrogen subsequent to right carotid artery ligation (“Levine preparation”). After a survival period of 24 h all animals developed typical ischemic lesions in the parietal cortex and to a lesser extent in the hippocampus of the hemisphere ipsilateral to the interrupted blood flow. The contralateral hemispheres were almost devoid of damage. The morphologic appearance of the brain tissue of animals pretreated with etomidate at a dose sufficient to induce hypnosis during the nitrogen exposures, resembled that of normoxic animals, suggesting that this drug preserved the structural integrity of the brain tissue. A hypnotic dose of thiopental also reduced neuronal damage to some extent. When exposure to nitrogen started after the rats complete recovery from hypnosis, etomidate still significantly suppressed the formation of lesions. These results indicate that etomidate, in addition to its hypnotic and anticonvulsant activities, is very effective in preventing cerebral damage induced by a severe hypoxic-ischemic insult and that the hypnotic effect does not seem to be essential in assuring this protection. There are several possible mechanisms by which this drug exerts its protective effects.

Global Incomplete Ischemia in Dogs Assessed by Quantitative EEG Analysis. Effects of Hypnotics and Flunarizine

Publisher Summary Incomplete but global ischemia is produced in dogs by two different experiments. In the first experiment described in the chapter, hypovolemia-hypotension is initiated by withdrawing arterial blood. After stabilization of the arterial blood pressure at 40–45 mm Hg for 15 min, saline, or the hypnotics etomidate, pentobarbital or thiopental are given in a bolus followed by an infusion. Eight cortical derivations are recorded on paper, online analysis are done of four cortical derivations, calculating the absolute power and off-line, the relative contribution of the power contained in seven predefined frequency bands to the total power are calculated. In the second experiment, global incomplete ischemia is produced by ligation of major vessels supplying blood to the brain. These arteries are occluded for 20-mins, with an interval of 72.5 min between each occlusion, repeated maximally three times. Comparison of the relative power in the delta- and beta-bands clearly indicated the progressive deterioration of the electroencephalogram (EEG) in conjunction with a decrease in cortical temperature (a qualitative measure of cerebral blood flow).

Ultrastructural damage and Ca2(+)-shifts in the canine myocardium subjected to regional incomplete ischemia.

SummaryThe role of Ca2+ in the pathogenesis leading to ischemic myocardial cell death is still controversial. To gain insight into this phenomenon a cytochemical procedure, the phosphate pyroantimonate method, was used to localize different subcellular Ca2+-pools at the ultrastructural level. After 45 min of left anterior descending coronary artery (LAD) occlusion, the coronary arteries were perfused with triphenyltetrazoliumchloride staining (TTC) to identify viable ischemic and infarcted tissue. In non-ischemic tissue, Ca2+-deposits were confined to the sarcolemma, sarcolemma-derived vesicles, transverse tubules, and intercalated disks. In infarcted tissue (TTC-negative), the sarcolemma lost its Ca2+-binding capacity and mitochondria were either overloaded with Ca2+-precipitate or they contained amorphous densities. In viable ischemic areas (determined with the TTC-technique) the sarcolemma was virtually devoid of Ca2+-deposits. Mitochondria in this area frequently showed clumping of the cristae, associated with an accumulation of Ca2+-precipitate in between the clustered cristae. The results of this study indicate that Ca2+-shifts occur in ischemic myocardial cells before the occurrence of other ultrastructural signs of irreversible injury which, therefore, narrows the possibility that Ca2+-overload is only a consequence of ischemic cell death.

A cardiac arrest model in rats for evaluating the antihypoxic action of flunarizine

Abstract Ventricular fibrillation was used to produce hypoxia in unanaesthetized rats. Flunarizine was given as hypoxia protectant in doses of 1 mg/kg i.v. just before fibrillation, which was induced with a small bipolar electrode catheter placed in the right ventricle. Aortic blood pressure (AoP), electrocardiogram (ECG) and the respiratory amplitude were recorded continuously. A significant lethality in the control group and the significantly enhanced recovery of ECG, AoP and respiration in the flunarizine groups make the model suitable to indicate antihypoxic actions of a drug.

A Dog Model to Evaluate Post-Cardiac Arrest Neurological Outcome

The success rate of cardiopulmonary resuscitation (CPR) in circulatory arrest (CA) even when performed by the most experienced emergency medicine groups is still less than 15%. The limit to final outcome is not the restoration of spontaneous circulation (ROSC) itself, but the events occurring following reperfusion of the brain by acid and toxic blood during CPR. The aim was to develop a dog model of ischemia in order to study the potential of physiological and pharmacological methods for restoring normal brain function after prolonged circulatory arrest.