Functional state of the cardiovascular system in 13-year-old adolescents with different types of autonomic nervous regulation

The features of the functional state of cardiovascular system in 13-year-old children with different types of autonomic nervous regulation were studied. Children with normotonic and parasympathetic types of autonomic regulation were found to have the highest adaptation capacities. The autonomic nervous system influences the bioelectrical processes in myocardium, the duration of cardiac cycle phases, and cerebral blood flow. Schoolchildren aged 13 years with higher sympathetic activity have shorter duration of the cardiac cycle, the phase of isometric contraction, and diastole. They have a lower pulse blood flow rate and a higher tone of large and medium cerebral vessels. No relationship was revealed between the initial autonomic nervous regulation of heart rate and the type of adaptation of myocardium to physical dynamic loads, as well as the type of adaptation of cerebral circulation to mental stress.     

Peculiarities of adaptation to systematic muscular activity in adrenalectomized rats

A 3 week training period in running restored the maximal swimming time of adrenalectomized rats to the level of intact untrained rats, but had no influence on the maximal running time and hepatic glycogen reserve. The cardiac hypertrophy and the augmentation of the Mg2+-activated ATPase activity of myocardium in adrenalectomized rats were more pronounced than in intact animals. It is concluded that the deficiency of adrenocortical hormones does not exclude all the adaptive alterations during training, although it makes the complete adaptation and normal increase of the working capacity impossible.     

Short-term adaptation of five- to seven-year-old children to mental load

Tetrapolar rheography according to Kubicek has been used to estimate the adaptive capacity of the cardiovascular system in 150 five- to seven-year-old children at rest and during mental load. Mental load evokes two variants of stroke volume (SV) responses, one of them characterized by an increase in the SV, and the other, by a decrease in the SV and an increase in the diastolic blood pressure (BP_d). Irrespective of the direction of the change in the SV, short-term adaptation to mental load in most five- to seven-year-old children does not stress the mechanisms of the cardiovascular system control and is generally favorable. In 13–15% of the children examined, short-term adaptation to mental load considerably stressed the cardiovascular system control. This is expressed in increased systolic blood pressure (BP_s), BP_d, and heart rate (HR); decreased CV and cardiac output (Q); and a prolonged restoration period for most central hemodynamic parameters.     

Characteristics of the myocardium functional state and cerebral circulation of seven- to ten-year-old children with different variants of autonomic nervous regulation of the heart rate

A complex study of the functional state of the cardiovascular system of seven- to ten-year-old children with different types of autonomic nervous regulation of the heart rate was performed. It was found that the autonomic nervous system strongly affects the adaptive capacity of the body, bioelectrical processes in the myocardium, the duration of cardiac-cycle phases, the pulse volume, and the tone of large and small cerebral vessels.     

Interrelations between the sympathoadrenal system,adrenal cortex,and autonomic tone in seven- to nine-year-old children

Comprehensive study of the functional state of the sympathoadrenal system (SAS) and adrenal cortex (AC) and the specific features of the autonomic regulation of the cardiac rhythm revealed close correlations between the excretion of catecholamines (CAs) and androgens, on the one hand, and the initial autonomic tone (IAT) of the cardiovascular system of children, on the other hand. Most schoolchildren of both sexes with a predominant dependence of their cardiac rhythm on sympathetic influences were shown to excrete more noradrenaline (NA), 17-hydroxycorticosteroids, and 17-ketosteroids and less dopamine than their normotonic and vagotonic counterparts, which was accompanied by an increase in the NA-to-adrenaline ratio. In contrast, eight-and nine-year-old girls exhibited a relatively decreased activity of glucocorticoid functions of the AC associated with sympathicotonia. A local static effort performed as a functional test caused similarly directed changes in the functional states of the SAS and AC in a manner dependent on the child’s IAT, age, and sex. In the states of sympathicotonia or normotonia, nine-year-old girls exhibited a decrease in the excretion of CAs and DOPA or their insignificant increase accompanied by strengthening of the functional activity of the AC, especially of its androgen function. This may be interpreted as a manifestation of specific neuroendocrine interrelations in the adaptive mechanisms of nine-year-old girls and a higher stability of the pituitary-adrenal system, which controls metabolic processes in the growing body. In contrast, in normotonic and vagotonic seven-year-old boys (as well as in sympathicotonic eight-year-old boys), the local static effort revealed simultaneous decreases in the reserve potentials of the SAS and AC, probably caused by fatigue and asthenization of these children during their schoolwork.     

Effect of sympathectomy on the heart pump function in rats during postnatal ontogenesis

The influence of guanetidine sympathectomy (30 mg/kg) on the heart pump function in rats during 3 weeks in postnatal ontogenesis has been investigated. Sympathectomy restrains age-dependent establishment of stroke volume, cardiac output and heart rate. The adaptation effects of regular physical training do not develop in the animals with sympathectomy, i.e. heart rate does not decrease and stroke volume does not increase. The initial stage of adaptation of the sympathectomized animals to physical training is accompanied by decrease in stroke volume and remarkable increase in heart rate which indicates the reduction of contractile activity in the myocardium.     

Increased enzymatic activity of antioxidant protection of the heart in the adaptation of rats to short-term stress exposure

It has been shown that adaptation to short-term emotional-painful stresses leads to an increase in antioxidant enzyme activities but does not change vitamin E content in the myocardium. The most labile enzyme was catalase (35% increase). During stress in nonadapted animals the enzyme activity decreased, as compared to the control, while in the group of adapted animals with subsequent stress the activity was even higher than in the control. During initiation of lipid peroxidation in the heart homogenates in vitro there was a 3-fold increase and a 1%-fold decrease in the oxidation intensity in rats exposed to stress and in adapted animals, respectively. The role of adaptation activation of cardiac antioxidant system in the prevention of stress-induced heart damage is discussed.     

Age-Related Features of Morphological and Functional Development of Myocardium in Children of Five to Nine Years

Age-related features of the morphological and functional development of the myocardium were studied by echo- (EchoCG) and electrocardiography (ECG) in 200 children five to nine years of age. The most intensive anatomical development of myocardium was observed at the age of five to seven years, and a significant increase in cardiac output was observed at the age of eight to nine years both in boys and girls. The ECG amplitude and time parameters significantly changed from of five to nine years of age and were most pronounced at the age of seven to eight years. Different changes in cardiac rhythm and excitation conduction as well as repolarization and metabolic disturbances in the myocardium were often observed at this age. Static physical exercise caused marked changes in bioelectric activity of the myocardium. Two types of central circulatory responses to static exercise were found: an increase and a decrease in cardiac output. The mechanisms of cardiac rhythm regulation, which caused an increase in the stroke volume as a response to exercise, were different in children from five to nine years old. At the age of five to six years the homeometric mechanism was a crucial factor in the increase in stroke volume as a response to exercise, and at the age of seven to nine years both homeo- and heterometric mechanisms of cardiac rhythm regulation were very important.     

Effect of hyperbaric oxygenation on several functional and morphologic properties of the heart and catecholamine metabolism in the presence of compensatory myocardial hypertrophy]

Rabbits subjected to hyperbaric oxygenation (HBO) for one month following ascending aorta stenosis developed less distinct hypertrophy and signs of myocardial dystrophy with a more distinct enhancement of the left ventricular contractility than animals with aortic stenosis kept under normal pressure. In rabbits with heart hypertrophy developing under HBO the increasing adaptive capacity of the myocardium was accompanied by an elevation in functional reserve of the sympathetic regulation apparatus. Apparently HBO aided the development of the optimum cardiac adaptation to a high afterload.     

Increased myocardial stiffness with maintenance of length-dependent calcium activation by female sex hormones in diabetic rats

A decrease in peak early diastolic filling velocity in postmenopausal women implies a sex hormone-related diastolic dysfunction. The regulatory effect of female sex hormones on cardiac distensibility therefore was evaluated in ovariectomized rats by determining the sarcomere length-passive tension relationship of ventricular skinned fiber preparations. Diabetes also was induced in the rat to assess the protective significance of female sex hormones on diastolic function. While ovariectomy had no effect on myocardial stiffness, collagen content, or titin ratio, a significant increase in myocardial stiffness was observed in diabetic rat only when female sex hormones were intact. The increased stiffness in diabetic-sham rats was accompanied by an elevated collagen content resulting from increases in the levels of procollagen and Smad2. Surprisingly, the increased myocardial stiffness in diabetic-sham rats was accompanied by a shift toward a more compliant N2BA of cardiac titin isoforms. The pCa-active tension relationship was analyzed at fixed sarcomere lengths of 2.0 and 2.3 μm to determine the magnitude of changes in myofilament Ca(2+) sensitivity between the two sarcomere lengths. Interestingly, high expression of N2BA titin was associated with a suppressed magnitude of changes in myofilament Ca(2+) sensitivity only in the diabetic-ovariectomized condition. Estrogen supplementation in diabetic-ovariectomized rats partially increased myocardial stiffness but completely reversed the change in myofilament Ca(2+) sensitivity. These results indicate a restrictive adaptation of myocardium governed by female sex hormones to maintain myofilament activity in compensation to the pathophysiological induction of cardiac dilatation by the diabetic condition.     

Effects of exercise training on cardiac function, gene expression, and apoptosis in rats

This study determined the effects of exercise training on cardiac function, gene expression, and apoptosis. Rats exposed to a regimen of treadmill exercise for 13 wk had a significant increase in cardiac index and stroke volume index and a concomitant decrease in systemic vascular resistance compared with both age-matched and body weight-matched sedentary controls in the conscious state at rest. In exercise-trained animals, there was no change in the expression of several marker genes known to be associated with pathological cardiac adaptation, including atrial natriuretic factor, beta-myosin heavy chain, alpha-skeletal and smooth muscle actins, and collagens I and III. Exercise training, however, produced a significant induction of alpha-myosin heavy chain, which was not observed in rats with myocardial infarction. No histological features of cardiac apoptosis were observed in the treadmill-trained rats. In contrast, apoptotic myocytes were detected in animals with myocardial infarction. In summary, exercise training improves cardiac function without evidence of cardiac apoptosis and produces a pattern of cardiac gene expression distinct from pathological cardiac adaptation.     

The prognostic significance of the adaptation potential of the cardiovascular system in 10- and 11-year-old children

Experimental physiological studies were made in 10–11-year-old boys and girls, students of a gymnasium and an education-upbringing complex. The functional parameters recorded in children momentarily included: the heart rate, systolic and diastolic arterial pressure, Roufier index, and the adaptation potential (AP) of the cardiovascular system as an integral index of the adaptivity level of human organism on the whole, measured according to special formulas, and the index of the risk of disease development. Apart from it, the height, body mass, vital lung capacity, and strength of hand grip were measured, the puberty stage and deviations in the functioning of organs and systems were revealed. The AP levels used to evaluate adults’ adaptation did not agree with 10–11-year-old children’s physical development degree, puberty stages, and health condition (belonging to different health groups). No agreement was found between the levels of these parameters and the degrees of AP of the cardiovascular system in 10–11-year-old children based on their individual values and sigmal deviations of this index. Therefore, a conclusion on the adaptation capacities of a child’s organism and the risk of disease development in it based on the AP values may be erroneous. The authors suggest an age scale of the AP levels for 10–11-year-old children.     

Effects of hibernation on mitochondrial regulation and metabolic capacities in myocardium of painted turtle (Chrysemys picta)

Painted turtles hibernating during winter may endure long-term exposure to low temperature and anoxia. These two conditions may affect the aerobic capacity of a tissue and might be of particular importance to the cardiac muscle normally highly reliant on aerobic energy production. The present study addressed how hibernation affects respiratory characteristics of mitochondria in situ and the metabolic pattern of turtle myocardium. Painted turtles were acclimated to control (25 degrees C), cold (5 degrees C) normoxic and cold anoxic conditions. In saponin-skinned myocardial fibres, cold acclimation increased mitochondrial respiratory capacity and decreased apparent ADP-affinity. Concomitant anoxia did not affect this. Creatine increased the apparent ADP-affinity to similar values in the three acclimation groups, suggesting a functional coupling of creatine kinase to mitochondrial respiration. As to the metabolic pattern, cold acclimation decreased glycolytic capacity in terms of pyruvate kinase activity and increased lactate dehydrogenase (LHD) activity. Concomitant anoxia counteracted the cold-induced decrease in pyruvate kinase activity and increased creatine kinase activity. In conclusion, cold acclimation seems to increase aerobic and decrease anaerobic energy production capacity in painted turtle myocardium. Importantly, anoxia does not affect the mitochondrial functional integrity but seems to increase the capacity for anaerobic energy production and energy buffering.     

Increase of calcium-dependent activity of phospholipase C in the myocardium in adaptation of animals to short-term stress effects]

The effect of adaptation of rats to repeated short-term stress exposures was studied on the density and the affinity of alpha 1-adrenoceptors in the heart and on the phospholipase C activity and sensitivity to changes in Ca2+ concentration. It was found that adaptation to stress was accompanied by a desensitization of alpha 1-adrenoceptors and also by an increase in Ca(2+)-dependence of phospholipase C activity in the heart. The role of increased activity of phospholipase C and activated inositol triphosphate-diacylglycerol regulatory cascade is discussed as regard to the previously revealed accumulation of heat shock proteins in the myocardium and to the adaptive protection of the heart.     

Adaptive Responses of Secretory Cardiomyocytes of the Right Atrium during Simulation of Microgravity Effects by Long-Term and Repeated Antiorthostatic Tail Suspension of Rats

Reactive changes in right atrial cardiomyocytes during antiorthostatic tail suspension of rats, which is commonly used to simulate effects of microgravity, have been studied by electron microscopy and morphometry. A 14-day tail suspension proved to increase contractile and secretory activities of cardiomyocytes. At the same time, signs of depleted activity are observed in some cells. Prolongation of the experiment to 30 days leads to development of adaptive compensatory responses and increases their secretory capacity. A 30-day rest in the normal orthostatic position does not completely restores the structure and functioning of cardiomyocytes and leads to accumulation of internal secretion in them. A repeated 14-day tail suspension to a certain extent facilitates cardiomyocyte adaptation to altered conditions as compared to a single exposure; apparently, secretion release decreases, while its production is activated.     

Seasonal adaptation of brown adipose tissue in the Djungarian hamster

Summary The composition and oxidative capacity of brown adipose tissue (BAT) were investigated in Djungarian hamsters kept under natural photoperiod, either indoors at neutralT _a (23°C) or under outdoor conditions. BAT comprises up to 5% of the body weight in summer/indoor hamster, with lipid representing 86% of the total tissue mass. Tissue mass and thermogenic capacity are inversely related during seasonal adaptation: 30% decrease of total DNA, accompanied by extensive lipid depletion, reduces the amount of BAT by almost 60% during acclimatization from summer/indoor to winter/outdoor conditions. Mitochondrial protein in BAT is increased by a factor of 2.6 concomitantly, and by a factor of 4 when related to body weight (body weight reduction 36%).Cytochrome oxidase activity in different brown fat deposits varies by up to 150% in summer/indoor hamsters; depending on the fat pad, the enzyme activity is increased 200%–700% during adaptation to winter/outdoor conditions.Natural photoperiod is decisive in determining the seasonal adaptation of DNA content in BAT and of body weight. Short photoperiod alone may lead to depletion of lipid content of BAT and thus decrease the tissue mass practically to the lowest seasonal level, even though both parameters may be also influenced byT _a. One third of the maximum adaptive increase of tissue mitochondria may be attributed to seasonal changes in photoperiod and up to two thirds toT _a. Photoperiod establishes a fixed fundament of slow-reacting functional adaptation of BAT, whereas the effect of decreasedT _a depends on the rate and duration of cold influence.Abbreviations BAT brown adipose tissue - NST nonshivering thermogenesis - T _a ambient temperature     

Effect of hemorrhage on plasma atriopeptin levels in conscious dogs

An increase in atrial pressure has been shown to cause an increase in the concentration of atrial peptides (atriopeptin) in plasma. We therefore hypothesized that a reduction in atrial pressure would decrease the concentration of atriopeptin in plasma. In formulating this hypothesis we assumed that changes in the concentration of other circulating hormones or changes in cardiac nerve activity during hemorrhage would not affect the secretion of atriopeptin. To test the hypothesis, we bled sham-operated conscious dogs at a rate of 0.8 ml.kg-1.min-1 to decrease right and left atrial pressures. Hemorrhage was continued until a total of 30 ml of blood per kilogram body weight had been removed. Identical experiments were performed on conscious cardiac-denervated dogs. The concentration of plasma atriopeptin was decreased in each group of dogs after 10 ml of blood per kilogram of body weight had been removed, but the decrease achieved statistical significance only in the cardiac-denervated dogs. Further hemorrhage, however, produced no further decreases in circulating atriopeptin in either group even though atrial pressures continued to decline as more blood was removed. A comparison of the atriopeptin response to hemorrhage revealed no significant difference between the sham-operated and cardiac-denervated dogs, thus providing no evidence for a specific effect of cardiac nerves on atriopeptin secretion during hemorrhage. Our results demonstrate that the relationship between atrial pressure and plasma atriopeptin that has been observed repeatedly during atrial stretch is not evident during relatively slow, prolonged hemorrhage. There is, however, a small decline in circulating atriopeptin during the initial stage of hemorrhage that could be of biological significance.