Effect of past stress on the resistance of the myocardium to hypoxia

The effect of emotional painful stress on myocardial contractility and resistance to hypoxia was studied on the rat isolated atrium. It was established that in stress-exposed rats, myocardial resistance to hypoxia was reduced and contractility was depressed. It was manifested in accelerated development and greater degree of hypoxic contracture, as well as in a slower recovery of myocardial contractility under reoxygenation. The decreased myocardial resistance to hypoxia under stress is suggested to be related to the stress-induced alterations in glycolysis and calcium transport in cardiomyocytes.     

Effect of geomagnetic activity on the rhythm of resistance of rats to hypoxia

The resistance of male Wistar rats to acute hypoxia was estimated from the lifetime at an "altitude" of 11.5 km above sea level from 13 to 21 p.m. and in different seasons of a year. Identical types of rhythms (circaseptan, circasemiseptan, infradian, circadian, and ultradian) of geomagnetic activity and lifetime were revealed. It was found that the periods of basal rhythms either coincide or are multiple. It was shown that the rhythms of geomagnetic activity (including nonbasal rhythms) affect lifetime rhythms (especially ultradian rhythms). As the periods of the rhythms decrease, the number of rhythms for both parameters increase (ultradian rhythms are most numerous), and relative differences in the values of periods (they are minimal for ultradian rhythms) and the amplitudes of rhythms decrease.     

Effect of adaptation to hypoxia on the resistance of rats to the epileptogenic action of penicillin

The influence of adaptation to moderate hypoxia on anticonvulsive resistance of low tolerant rats has been investigated. Focal epilepsy was induced by penicillin application to sensorimotor cortex of the rat brain. Adaptation to hypoxia has been shown to increase the resistance of rats to epileptogenic penicillin effect which is manifested in the prolongation of the latent period of epileptiform discharges and less frequent epileptic fits. The mechanisms of the resistance increase remains to be investigated.     

Studies on the mechanisms of resistance to hypoxia a review

The review summarises results of experimental research in Russia.The ultimate response mechanism of the hypoxic stimulus appears to reside in the cell itself and is activated by the direct action of nervous stimulation on the tissues involved and/or various hormonal regulatory systems.The adaptive mechanism in the cell to hypoxia involves a change in the cellular metabolism mediated by various enzymatic alterations. These cellular alterations,according to the principle of negative feedback, readjust the control of the nervous input from the lower and higher regulatory centers to a level corresponding to the changed environmental stimulus. Therefore, a new level in the coordination of the functional systems is established and the organism's general resistance is enhanced to hypoxia, the ultimate stimulus.

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Zusammenfassung Die ist ein Bericht über experimentelle Untersuchungen in Russland. Der letzte Reaktionsmechanismus auf den hypoxischen Reiz scheint in der Zelle selbst zu liegen und wird aktiviert durch nervale Erregung des betreffenden Gewebes und/oder verschiedene homonale Regulationssysteme. Der Anpassungsmechanismus in der Zelle bei Hypoxie schliesst einen Wechsel des Zellstoffwechsels ein durch Veränderung der Enzymmuster. Diese zellularen Veränderungen führen über ein negatives feedback System zu einer Kontrolle der nervalen Erregung, die von den niedrigeren und höheren Regulationszentren ausgehen, auf ein Niveau, dass der Änderung des Umweltreizes entspricht. So wird ein neues Gleichgewicht in der Koordination der funktionellen Systeme erreicht, das durch erhöhte Hypoxie-Resistenz gekennzeichnet ist.

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Resume Il s'agit ici d'un rapport concernant des recherches expérimentales effectuées en URSS. Le dernier mécanisme réactionnel d'une irritation hypoxique semble résider dans la cellule elle-même et être activé par un influx nerveux au niveau du tissus spécifique et/ou par différents systèmes de régularisation de nature hormonale. Le mécanisme d'adaptation de la cellule en cas d'hypoxie entraîne un changement du métabolisme interne conditionné par diverses altération des enzymes conduisant. Ces modifications cellulaires rétablissent, par un système de rétrocessions négatif, le contrôle de l'influx nerveux qui, des centres de régularisation supérieurs ou inférieurs, réagit au niveau auquel les modifications de la stimulation dues au milieu ambiant se sont produites. Il s'établit ainsi un nouvel équilibre dans la coordination des systèmes fonctionnels, équilibre caractérisé par une résistance accrue à l'hypoxie.

     

Effect of systemic hypoxia and reoxygenation on electrical stability of the rat myocardium: chronophysiological study

The aim of the study was to determine the dependence of changes in the electrical stability of the heart on the light-dark cycle (LD cycle) in disorders of pulmonary ventilation. The ventricular arrhythmia threshold (VAT) was measured in female Wistar rats (adaptation to the light regime 12:12 h, ketamine/xylazine anesthesia 100 mg/15 mg/kg, i.m., open chest experiments). The conditions of the normal artificial ventilation and reoxygenation were V(T) = 1 ml/100 g, respiratory rate 40 breaths/min, hypoventilation V(T) = 0.5 ml/100 g, respiratory rate 20 breaths/min. The animals (n=11 light group; n=19 dark group) were subjected to 20 min hypoventilation followed by 20 min reoxygenation. The control prehypoventilatory VAT differences were not found between the light (1.90+/-0.84 mA) and dark (1.88+/-0.87 mA) part of the day. Artificial hypoventilation changed the VAT values in light and dark part of the day differently. While during the light period, the average VAT values in most animals (90.9 %) were significantly decreased (1.29+/-0.59 vs. 1.90+/-0.84 mA control, p<0.05), during the dark part these values showed either significant increase (63.2 %) (2.23+/-0.77 vs. 1.48+/-0.39 mA, p<0.005) or a slight non-significant decrease (36.8 %) (2.18+/-0.89 vs. 2.54+/-0.99 mA). Reoxygenation returned the VAT values to the level before hypoventilation by an increase of the VAT (81.8 %) in the light part of day and by decrease of the VAT (68.4 %) in the dark part of the day. It is concluded that 1) in hypoventilation/reoxygenation model, the significant higher average VAT values are in the dark part of the day vs. the light one, 2) rat hearts are more resistant to systemic hypoxia and reoxygenation in the dark part of day, and 3) proarrhythmogenic effect of the systemic hypoxia is only seen in the light part of the day.     

Psychosomatic factors of resistance to hypoxia

During formation of human long-term adaptation to cold-hypoxic influence, the some dynamics of psychological mechanisms contribution was revealed. On the first step of adaptation process, emotional-volitional personal peculiarities are significantly contributing; on further steps, communicability and general learning abilities are gaining importance. Anxiety, tenseness, diffidence and too strong self-control limit the hypoxic resistance far before restriction of physiological markers of the organism's functional abilities. Adaptation to cold-hypoxic effect contributing to organism stress-limiting system is believed to help experiencing extreme somatic and psychic loads by the people from psychological risk group.     

Effects of adaptation to exposure to short-term stress on indices of resistance of energy metabolism and contractile function of the myocardium to acute hypoxic hypoxia and reoxygenation

Effect of preliminary adaptation to immobilization stress with progressive duration from 15 min. to 1 h (every second day, 8 sessions) on the resistance of indices of myocardial energy metabolism and contractile function to acute hypoxic hypoxia and subsequent reoxygenation was studied. It was shown, that adaptation to short-term stress exposure by some way provided the retention of activities of important enzymes like creatine-phosphokinase and phosphorylase under the harmful action of acute hypoxia and subsequent reoxygenation. At the same time, the ATP restoration and the CP super-restoration were observed during reoxygenation. This effect, in its turn, was accompanied by a more pronounced super-restoration of the heart contractile function than in control.     

Effect of the Pro-Gly-Pro peptide on resistance of rats to acute hypobaric hypoxia and posthypoxic behavioral disorders

Outbred white rats were subjected to acute hypobaric hypoxia in an altitude chamber at a reduced pressure of 145 mm Hg. Parameters of behavioral activity were evaluated in the tests of elevated cross maze and hole chamber and by the Porsolt method. Posthypoxic behavioral changes were characterized by an increase in the level of anxiety and depression and by a decrease in the level of orienting and exploratory activity. Preliminary intraperitoneal administration of the peptide 15 min before the hypoxia at a dose of 3.7 mol/kg increased the coefficient of individual resistance of the animals owing to a decrease in restitution time and significantly decreased posthypoxic behavioral disorders. We previously found that the Pro-Gly-Pro peptide had positive influence on homeostasis and maintained an adequate blood supply to organs and tissues. It was proposed that this ability of the Pro-Gly-Pro peptide could be one of the important mechanisms for its protective antihypoxic effect.     

Effects of manganese chloride, verapamil, and hypoxia on the rate-dependent increase in internal longitudinal resistance of rabbit myocardium

The effects of high rates of stimulation on the internal longitudinal restivity (Ri) and conduction velocity (theta) were studied on rabbit papillary muscle preparations using a silicon-oil chamber. Increasing the rate from 75 to 150/min caused Ri to rise and theta to decrease. The maximum rate of depolarization and action potential duration were also decreased. At a rate of 300/min the effects were more pronounced. Blockade of the slow inward current (Isi) and of the Na-Ca exchange by MnCl2 (5 mmol/L) did not prevent rate-induced changes in these variable. Verapamil (0.02 mmol/L) was also ineffective. Hypoxia (PO2 = 5.3 kPa) at 75/min induced changes in Ri and theta which were similar to those recorded at 150/min under aerobic conditions. The effects of high rates of stimulation were potentiated under hypoxia. From the present results it is suggested that Isi and the Na-Ca exchange are not the main determinants of the rate-induced increase in Ri, which could be determined by other intracellular Ca-release mechanisms or by a decrease in myoplasmic pH.