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Biomedical subjects

A Viru

Publications and source records attributed to A Viru.

At least 37 records · Page 2Linked to original sources
PubMed1995

Pre-exercise serum cortisol concentration and responses to laboratory exercise.

Relationships between the postexercise values of blood lactate concentration, pH, oxygen uptake, heart rate, power output on the one hand, and the pre- and postexercise blood cortisol concentrations on the other, were studied in 74 male and 40 female athletes (wrestlers and senior and junior rowers), performing graded exercise of increasing intensity. The senior rowers, junior rowers and wrestlers had different exercise protocols. The senior rowers of both sexes had significantly higher rest concentrations of serum cortisol than the junior athletes. A significant correlation between postexercise lactate concentrations and pre-exercise cortisol concentrations was found in all the male groups ("common" r = 0.515, P < 0.001), but not in the female ones (r = 0.162). It was concluded that the pre-exercise cortisol concentrations might condition anaerobic-glycolytic metabolism in physical exercise.

Adolescent↗
PubMed1995

Plasma endorphin species during dynamic exercise in humans.

beta-Endorphin is metabolized to gamma- and alpha-endorphin. In order to evaluate endorphin metabolism during exercise, radioimmunoassay blood levels of alpha-, beta- and gamma-endorphins were recorded during exercise for 2 h on a cycling ergometer in 12 endurance-trained and 11 untrained male subjects. In untrained subjects, mild exercise (49 +/- 4% VO2max, mean +/- SD) did not show an increase in plasma beta-endorphin, while the levels of its metabolites rose. No changes were noted in the endurance-trained subjects. More intensive exercise (66 +/- 6% VO2max in untrained and 57 +/- 7% VO2max in trained subjects) resulted in an increase in beta-endorphin concentration in association with elevation of the alpha-endorphin level. While before and during exercise the beta-endorphin levels did not differ significantly between athletes and untrained subjects, the levels of gamma- and alpha-endorphins, as well as the molar ratios alpha/beta and gamma/beta, were significantly higher in untrained subjects. In conclusion, blood levels of beta-endorphin metabolites in the resting state and during exercise are dependent on previous training. In untrained subjects, mild exercise may result in accumulation of gamma- and alpha-endorphins in blood without a concomitant change in beta-endorphin level.

Adult↗
PubMed1995

Effect of postexercise sucrose administration on liver glycogen repletion in rats.

In Wistar rats after swimming for 3 h, the glycogen level remained low in the liver during a period of 7 h. When sucrose was administered immediately after exercise, the liver glycogen content increased rapidly. From the 3rd to the 5th postexercise hour a secondary reduction was observed in hepatic glycogen. Sucrose administration inhibited the reduction of the blood glucose concentration which increased during exercise. However, 7 h after exercise, a slight hypoglycemia occurred in sucrose-treated rats. Administration of sucrose as a bolus immediately after exercise does not ensure a complete refilling of the hepatic glycogen store.

Animals↗
PubMed1995

Health promotion and exercise training.

Health is determined not only by the absence of disease, but also by an individual's resistance to pathogenic factors. In turn, resistance depends on the effectiveness of specific homeostatic regulation and the mechanism of general adaptation. Through the change in adaptivity, health may be increased or reduced. While it is difficult to predict which specific homeostatic mechanism will be necessary in various stages of life in the individual, it is more reliable to try to improve health, thereby increasing the effectiveness of the mechanism of general adaptation. Physical training results in a variety of changes in individuals. There are several changes which are essential both for increased exercise performance and for increasing adaptivity, by favouring the effectiveness of the mechanism of general adaptation. These changes: improve central nervous regulation and central nervous system functions; increase endocrine system capacity; increase energy potential; improve the capacity of the oxygen transport system; improve oxidation processes; increase metabolic and functional economy; increase functional stability; and increase the number of Na+,K+ -pumps. The influence of these changes on adaptivity is accomplished by the influence of exercise training on immunoactivities, and by the antisclerotic effect of training. The latter may be considered to be metabolic (actualised through the training effect on lipoprotein metabolism and aging-related calcium distribution) or mechanical (protection of tissues from sclerotic changes by their activities) effects. The training effects are specifically dependent upon performed exercises. Endurance exercise is considered to be the most important and widely recommended form of exercise for health improvement. Most of the training benefits (listed above) for increased adaptivity are induced by aerobic endurance training. Gymnastic exercises are indispensable in regard to mechanical antisclerotic effect. They are also essential influences on the central nervous system. Aerobic dance or aerobic rhythmic gymnastics are ways by which the positive effects of endurance and gymnastic exercise can be combined.

Adaptation, Physiological↗
PubMed1994

Glucocorticoids in metabolic control during exercise: alanine metabolism.

To evaluate glucocorticoid participation in the control of alanine metabolism during exercise, experiments were performed on adrenalectomized and normal male rats. The adrenal insufficiency prevented the rises induced by 3 h of swimming in alanine levels of blood plasma, red portion of quadriceps, and liver. In normal rats, the rise in alanine content by 65% in blood, 50% in fast-twitch oxidative fibers, and 93% in liver was associated with increased activity of alanine aminotransferase in fast-twitch oxidative-glycolytic fibers (by 23%). In adrenalectomized rats, enzyme activity during exercise did not change in muscles and decreased in hepatic tissue (by 25%). The dependence of exercise-induced changes in alanine aminotransferase activity on glucocorticoids was confirmed by an increased enzyme activity (by 53%) in exercised adrenalectomized rats treated with 125 micrograms corticosterone. In normal rats, training prevented both the rise of blood corticosterone and the activation of hepatic alanine aminotransferase during exercise. The results support the view that the stimulation of the glucose-alanine cycle by glucocorticoids promotes alanine supply and utilization in liver during exercise. In adrenalectomized rats, hepatic arginase activity was decreased during exercise and no elevation of urea levels was found in blood, liver, or skeletal muscles. Consequently, the use of products of the deamination of alanine (and other amino acids) for urea formation also depends on glucocorticoids.

Adrenalectomy↗
PubMed1994

Molecular cellular mechanisms of training effects.

The review paper was composed in order to (1) discuss the mechanism responsible for the actualization of the adaptive protein synthesis in training, and (2) indicate the necessity for further studies in this field. Genome activation is common for systematic exercising. Depending on the specific nature, exercises result in the formation of metabolic and hormonal inductors acting on the cellular genetic apparatus. The final results of the adaptive protein synthesis are determined by the combination of influences exerted by transcription, translation and post-translation control.

Adaptation, Physiological↗
PubMed1994

Glucocorticoids in metabolic control during exercise: glycogen metabolism.

In order to evaluate the participation of glucocorticoids in the control of glycogen metabolism during exercise, experiments were performed on male adrenalectomized and normal rats. In adrenalectomized rats swimming for 4 hours induced less pronounced increases in lactate concentrations in skeletal muscles than in normal rats (in FG fibers up to 10.7 +/- 1.0 vs 14.8 +/- 1.2 and in SO fibers up to 9.1 +/- 0.7 vs 12.5 +/- 0.7 mg x g-1 wet tissue). The glycogen drop in liver and oxidative muscles was also less pronounced (in liver by 14% vs 52%, in SO fibers by 33% vs 54% in normal rats). Swimming until exhaustion led to an extremely low glucose level in blood (1.89 +/- 0.12 mMol x L-1) in adrenalectomized rats. When they were treated with dexamethasone, the swimming duration was longer (12 +/- 1 hours vs 9 +/- 0.8 hours in saline treated), blood glucose level at exhaustion was higher (3.07 +/- 0.23 mMol x L-1) and the drop of hepatic and muscle glycogen was more pronounced. In normal rats hepatic glycogen content dropped by 68% after swimming for 4 hours. After swimming for 8 or 12 hours further decreases in hepatic glycogen content were insignificant. High levels of corticosterone in blood was found after swimming for 4 and 8 hours. After swimming for 16 hours corticosterone concentration was below normal and a new drop in liver glycogen (until a level constituting only 11% initial) was recorded. The results support the suggestion that glucocorticoids, regulate hepatic glycogen and peripheral glucose utilization during exercise, and also participate in the control of glycogenolysis in muscles.

Adrenal Glands↗
PubMed1993

Steroid and pituitary hormone responses to rowing: relative significance of exercise intensity and duration and performance level.

To analyse the relative significance of exercise intensity and duration as well as performance capacity, hormone changes were recorded in 16 male rowers in two experiments separated by a year. The test exercises consisted of 7-min (at the supramaximal intensity) and 40-min rowing (at the level of the anaerobic threshold) on a rowing apparatus. In addition, somatotropin and cortisol responses were estimated in rowing for 8 x 2000 m in 14 rowers of national class. All three tests caused significant increases in somatotropin and cortisol concentrations in the blood. Follitropin concentrations were elevated in the 7-min exercise test in the second experiment and in the 40-min exercise test in both experiments. Lutropin and progesterone concentrations increased during the more prolonged exercise in the first experiment. No common change was found in testosterone concentrations. Cortisol and somatotropin response to the 40-min rowing test at anaerobic threshold were more pronounced than to the 7-min exercise test at supramaximal intensity. When the rowers achieved a national class level of performance (the second experiment) the hormone responses to 7-min supramaximal exercise were increased. During the 8 x 2000-m rowing test cortisol but not somatotropin concentration increased to an extremely high level in the rowers of national class. It is concluded that in strenuous exercise cortisol and somatotropin responses were triggered by the exercise intensity threshold. The exact magnitude of the response would seem to have depended on additional stimuli caused by exercise duration and on possibility of mobilizing hormone reserves.

Adolescent↗
PubMed1993

Elevation of cortisol and growth hormone levels in the course of further improvement of performance capacity in trained rowers.

In 30 rowers plasma growth hormone and cortisol responses to a 7-min test on a rowing apparatus, performed at the highest possible rate, or to a competition race of 2000 m were recorded three times during a period that lasted up to 20 months. Apart from an improvement of the results in competition the increased performance capacity was also indicated by means of power output during the 7-min test (from 363 +/- 8 to 425 +/- 7 W in group A and from 382 +/- 7 to 437 +/- 9 W in group B). A pronounced rise was found in pre-exercise (in group A) and post-exercise (in both groups) cortisol levels. Post-exercise growth hormone levels increased when the rise in the mean power output was 40 W. Significant correlations were revealed between group values of power output and hormone levels during the study period. The performance capacity correlated with growth hormone levels after competition. The highest values were found in 10 elite rowers, studied additionally during an international competition. In cortisol values this kind of dependence was not found. Only the pre-competition concentrations of cortisol were significantly higher in elite rowers than in rowers of lower performance levels. Thus a further improvement of the performance capacity in previously trained sportsmen is associated with elevated growth hormone and cortisol levels in supramaximal exercises.

Adaptation, Physiological↗
PubMed1993

Lipolytic actions of hormones on adipocytes in exercise-trained organisms.

Adipocytes from sportsmen exhibited lower basal rate of lipolysis but higher response to adrenaline than those from untrained persons. Dexamethasone exposure for 30 min enhanced the adrenaline effect both in sportsmen and trained rats. Insulin abolished this glucocorticoid action. A rapid permissive action of glucocorticoids was suggested in the trained organism.

Adipose Tissue↗
PubMed1992

Adipocyte responses to adrenaline and insulin in active and former sportsmen.

The rates of lipolysis and lipogenesis in adipocytes, isolated from biopsy samples of subcutaneous fat, was assessed by estimation of glycerol release during a 30-min incubation, and of the incorporation of 14C-glucose into lipids during a 1-h incubation at 37 degrees C, respectively. The subjects were six highly-qualified, active endurance sportsmen, eight former endurance sportsmen of international class, and six untrained young men. In the active sportsmen the basal rate of lipolysis was about half of that in the previously-active sportsmen and the untrained subjects, but after the addition of adrenaline (10(-4) or 5 x 10(-4) mol.l-1) the lipolysis rate was the highest. No differences were observed in the lipolytic rates in the former sportsmen compared to the untrained subjects. Gases of a comparatively high level of lipogenesis were found in the trained subjects. The addition of insulin (9 microU.ml-1) to isolated adipocytes caused a significant augmentation of individual rates of lipogenesis in the active sportsmen and the untrained persons but not in the previously-active sportsmen. In comparison with the active sportsmen, the previously active sportsmen revealed an increased basal rate of lipolysis and a reduced sensitivity to the lipogenic action of insulin. These findings suggest that these changes may have had significance in avoiding an increase of adipose tissue after a decrease in energy expenditure due to a change in physical activity.

Adipose Tissue↗
PubMed1992

Mechanism of general adaptation.

An analysis of theories and results of corresponding studies indicate that the adaptive processes in organisms have to be discriminated to specific and nonspecific adaptive responses. The integrated sum of specific adaptive responses constitute homeostatic regulation in order to maintain a constant level of rigid constants of the body's internal milieu. The constancy of rigid constants (temperature, pH, osmotic pressure, and contents of ions, water and p0(2)) is necessary to ensure the optimal activity of enzymes. The nonspecific adaptive responses are directed towards the mobilization of the organism's reserves for energy and protein synthesis. Additionally, a general activation of the body's defence faculties is included into the nonspecific adaptive responses. The nonspecific adaptive responses constitute a coordinated mechanism of general adaptation. The mobilization of the reserve for protein synthesis is connected with induction of the adaptive synthesis of the enzyme and structural proteins in order to restore and develop the functional capacity of cellular structures that were highly active during acute influence of various stressors.

Adaptation, Physiological↗
PubMed1992

Plasma hormones and physical exercise.

The analysis of published data allowed us to establish main traits of blood hormone responses to exercises: There are stable changes in hormone levels that are common to all persons, as well as changes which are characterized by a polyphasic pattern and exhibiting inter-individual variability. By the response rate it is possible to discriminate fast responses, responses of a modest rate and delayed responses. Accordingly, mechanisms for a rapid and for a delayed activation exist. The changes mediated through the mechanism for a rapid activation depend on the intensity of exercise, revealing the threshold intensity for endocrine response. When a certain amount of exercise is done, the hormonal responses are triggered despite the under-threshold intensity of exercise. Consequently, a threshold duration of exercise also exists. Through training the threshold intensity of exercise increases and the functional capacities of the endocrine systems augment. The former results in the disappearance of hormonal responses during exercise intensity which was previously above the threshold. The latter makes it possible to achieve especially pronounced and long-lasting hormonal changes during extreme exercises. Emotional states as well as environmental conditions, and carbohydrate supply modulate the hormonal changes in exercise.

Exercise↗
PubMed1992

Stability and variability in hormonal responses to prolonged exercise.

To study the dynamics of alterations in blood hormones and their individual variability during prolonged exercise, changes in plasma levels of corticotropin, cortisol, aldosterone, testosterone, progesterone, somatotropin, insulin and C-peptide were recorded in 32 endurance athletes and 50 untrained persons during a 2-hour exercise on a cycle ergometer at 60% VO2max. Common changes were activation of the pituitary corticotropin function, mostly at the end of exercise, rises in aldosterone and somatotropin concentrations and decreases in insulin and C-peptide levels during exercise. The activation of pituitary-adrenocortical system and the decrease of insulin but not C-peptide levels were more pronounced in athletes than in untrained persons. A large inter-individual variability existed in changes of cortisol, testosterone and progesterone in both groups. Five variants were found in the dynamics of cortisol concentration. Whereas the alterations of corticotropin were characterized mainly by a biphasic increase, the dynamics of corticotropin and cortisol coincided only in one variant out of five. Most characteristic for the postexercise recovery period were decreased activity of the pituitary-adrenocortical system and delayed normalization of aldosterone level.

Adolescent↗
PubMed1992

Exercise-induced catabolic responses in various muscle fibres.

In Wistar rats a 10-hr swim caused an immediate increase of 3-methylhistidine and free tyrosine content in the white portion of quadriceps muscle. In the red portion the elevated levels of these amino acids were observed within 6 to 48 hrs of postexercise recovery. The glycogen depletion was substantially higher in the red portion of the muscle, indicating that the most active were oxidative-glycolytic fibres during the exercise. In conclusion, during exercise the most active muscle fibres do not contribute to the mobilization of protein resources. In a later part of postexercise recovery, catabolic changes occur in most active fibres, constituting, reasonably, a part of enhanced protein turnover.

Animals↗
PubMed1991

Adaptive regulation of hormone interaction with receptor.

Results of various studies suggest the existence of regulatory factors controlling the interaction of hormone with receptor and the postreceptor processes. Hence, the hormone effect is actualized through private and attending regulations. The first consists in the induction of specific effects of the hormone in target tissues. The attending regulation is realized as: 1) modulating regulation, acting on the state and number of cellular receptors, 2) metabolic regulation, acting via the other receptors on the cellular metabolism and changing in such a way the actualization of private regulation, 3) regulation of protein synthesis, acting on the synthesis of structure and enzyme proteins, participating in the actualization of private regulation. In physiologic meaning the modulating regulation consists in guaranteeing (to maintain the accordance between numbers of binding sites and acting signal molecules), homeostatic (to maintain the hormone balance through the alterations on the receptor level) and stress (to facilitate the regulatory effects through changes on receptor or postreceptor levels) regulations.

Animals↗
PubMed1991

Exercise-induced changes of endorphin contents in hypothalamus, hypophysis, adrenals and blood plasma.

Changes of alpha-, beta-, and gamma-endorphin contents were determined in hypothalamus, hypophysis, adrenals and blood plasma in Wistar rats. Four hours of swimming in water at 32 +/- 1 degrees C caused a decrease of the beta-endorphin content in hypophysis and hypothalamus. In adrenals, beta-endorphin did not change. Changes of alpha- and gamma-endorphins were not parallel to alterations of beta-endorphin. In blood plasma, levels of both alpha- and gamma-endorphins were elevated. After 7 days of swim training, 4 hours of swimming caused a slight increase of alpha-, beta- and gamma-endorphin levels in hypophysis as well as a pronounced increase of alpha- and beta-endorphins in adrenals. In hypothalamus, beta-endorphin content was decreased, but alpha-endorphin content was on the level of sedentary controls, gamma-endorphin content doubled. The levels of endorphins in blood were higher than after a single swimming bout. It was concluded that during acute exercise the activation of the opioid system is mainly based on the augmented release of beta-endorphin. In daily repeated exercise the production of beta-endorphin increases and exceeds the elevated release in hypophysis and adrenals.

Adrenal Glands↗