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Biomedical subjects

K Nazar

Publications and source records attributed to K Nazar.

At least 37 records · Page 2Linked to original sources
PubMed1999

The influence of endurance training on the transient haemodynamic response to orthostatic manoeuvre.

Several investigations demonstrated that aerobic fitness is associated with a tendency towards orthostatic hypotension whereas other reports did not show any differences in cardiovascular adjustment to orthostatic challenges between endurance trained and sedentary subjects. In the present work, the time course of changes in heart rate (HR), systolic time intervals (STI), stroke volume (SV), cardiac output (CO) and blood pressure was studied during 8 minutes following standing up from supine position in 7 healthy volunteers before and after 10 weeks of endurance training on bicycle ergometer. Impedance cardiography was used for measurement of cardiac postural responses. The training program applied in this study increased the subjects' aerobic capacity (VO2max) by approx. 18%. After training, the steady-state supine HR and contribution of the pre-ejection period and ejection time to the total R-R interval in ECG were lowered while SV was significantly increased. No significant training-induced changes were found in magnitude and time-courses of HR, STI, SV and CO changes following standing up. Diastolic blood pressure during standing was greater after than before training. It is concluded that the short-time endurance training does not affect adversely cardiovascular orthostatic response and may even improve orthostatic tolerance due to the augmentation of diastolic blood pressure response.

Adult↗
PubMed1998

Psychomotor performance during prolonged exercise above and below the blood lactate threshold.

Previous investigations from this laboratory have demonstrated that during graded exercise with exercise intensities increasing every 3 min until exhaustion the multiple choice reaction time (RT) decreased until the intensity exceeded the lactate threshold (LT) by approximately 25%, and then rapidly increased. The aim of this study was to follow up changes in RT during prolonged exercise at constant intensities above and below LT and to relate these changes to changes in venous blood lactate [La-]b, and plasma catecholamine [CA]pl concentration responses to the exercise. For this purpose eight young soccer players exercised for 20-min on a cycle ergometer at 10% above LT, and nine exercised for 60 min at an intensity 30% below LT. During both tests RT, heart rate (HR), as well as [La-]b, and [CA]pl were measured. Above LT, RT decreased from the 5th min until the end of exercise, whilst HR, [La-]b, and [CA]pl increased progressively. Significant inverse correlations were ascertained between RT and plasma adrenaline (r = -0.651) and noradrenaline concentrations (r = -0.678). During exercise below LT, RT decreased up to approximately 40 min, then it reached a nadir, and stabilized at this level. This was accompanied by only small changes in [La-]b and [CA]pl. The present findings would indicate that young athletes are able to maintain for a relatively long time, or even increase, their psychomotor performance during endurance exercise both below and above the LT.

Adult↗
PubMed1998

Effect of a short-term dietary creatine supplementation on high-energy phosphates in the rat myocardium.

The aim of this study was to find out whether creatine (Cr) feeding affects total creatine (TCr), phosphocreatine (PCr), adenine nucleotide contents and beta-hydroxy-acyl-CoA-dehydrogenase (HAD) activity in myocardium as compared to red skeletal muscle. Ten adult Wistar rats received Cr (2.5% of diet weight) for 7 days. In Cr fed rats, PCr was increased (by approx. 20%) in cardiac and in soleus muscles with ATP elevated in myocardium and TCr and free Cr in soleus. In both muscles, Cr feeding enhanced HAD activity. It is concluded, that dietary Cr does increase cardiac muscle high energy phosphate reserves and its oxidative potential.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1998

Comparison of changes in glucose tolerance and insulin secretion induced by three-day bed rest in sedentary subjects and endurance or strength trained athletes.

Restriction of physical activity causes exaggerated hyperinsulinemia and hyperglycemia following an oral glucose load. It is attributed to decreased sensitivity to insulin and decreased GLUT-4 transporter content in skeletal muscles. On the other hand, both endurance and strength training enhance whole body insulin sensitivity. Apart from increased insulin action in skeletal muscles, muscle hypertrophy is considered as the mechanism responsible for the training effect. Our previous study showed, that after three days of bed rest the plasma insulin response to a glucose load markedly increases both in untrained and in endurance-trained subjects; but the blood glucose (BG) response was less affected in athletes. The present investigation was designed to compare an effect of three day bed rest on BG and plasma insulin responses to oral glucose in untrained subjects, and in endurance or strength trained athletes. There are reports that the sympathetic nervous system activity is inhibited by bed-rest. Activation of this system after carbohydrate ingestion is considered an important mechanism contributing to dissipation of excess energy and prevention of postprandial fall in blood pressure. Thus, the second purpose of the present investigation was to find out whether short-term bed rest modifies changes in plasma catecholamines, heart rate and blood pressure following glucose ingestion.

Adult↗
PubMed1998

Relationship between EMG blood lactate, and plasma catecholamine thresholds during graded exercise in men.

The aim of this study was to follow up the electromyographic activity (EMG) of dynamically working muscles with simultaneous determinations of blood lactate and plasma catecholamine concentrations during progressive exercise. Twenty eight male soccer players aged 20.6 +/- 0.8 yrs performed incremental bicycle ergometer exercise test. The test consisted of 3-min stages exercise separated by 1-min rest intervals. Work load at each stage increased by 50 W until volitional exhaustion. The root mean square (rms)-EMG activity of the rectus femoris and soleus muscles were recorded continuously during exercise. Venous blood samples were taken after each exercise stage for determination of blood lactate (LA). Additionally in seven subjects adrenaline (A) and noradrenaline (NA) concentrations were determined. The EMG activity increased negligibly during exercise of low to moderate intensities revealing an abrupt rise at the load corresponding to thresholds of blood lactate and plasma catecholamine accumulation (LA-T, A-T, NA-T). Close correlations (P < 0.001) were found between blood LA concentration and EMG derived from rectus f. (r = 0.72) and soleus (r = 0.68) muscles. The mean threshold exercise intensities for m. rectus f. and m. soleus EMG (176 +/- 9 W and 172 +/- 9 W, respectively) did not differ significantly from lactate (164 +/- 7 W), noradrenaline (178 +/- 6 W) and adrenaline (180 +/- 5 W) thresholds, all of them detected by log-log transformation. The results indicate that threshold character of EMG changes in dynamically working muscles reflects to some extend the patterns of blood lactate and plasma catecholamine changes during incremental exercise.

Adult↗
PubMed1997

The effect of a low-carbohydrate diet on performance, hormonal and metabolic responses to a 30-s bout of supramaximal exercise.

The aim of this study was to find out whether a low-carbohydrate diet (L-CHO) affects: (1) the capacity for all-out anaerobic exercise, and (2) hormonal and metabolic responses to this type of exercise. To this purpose, eight healthy subjects underwent a 30-s bicycle Wingate test preceded by either 3 days of a controlled mixed diet (130 kJ/kg of body mass daily, 50% carbohydrate, 30% fat, 20% protein) or 3 days of an isoenergetic L-CHO diet (up to 5% carbohydrate, 50% fat, 45% protein) in a randomized order. Before and during 1 h after the exercise venous blood samples were taken for measurement of blood lactate (LA), beta-hydroxybutyrate (beta-HB), glucose, adrenaline (A), noradrenaline (NA) and insulin levels. Oxygen consumption (VO2) was also determined. It was found that the L-CHO diet diminished the mean power output during the 30-s exercise bout [533 (7) W vs 581 (7) W, P < 0.05] without changing the maximal power attained during the first or second 5-s interval of the exercise. In comparison with the data obtained after the consumption of a mixed diet, after the consumption of a L-CHO diet resting plasma concentrations of beta-HB [2.38 (0.18) vs 0.23 (0.01) mmol x l(-1), P < 0.001] and NA [4.81 (0.68) vs 2.2 (0.31) nmol x l(-1), P < 0.05] were higher, while glucose [4.6 (0.1) vs 5.7 (0.2) mmol x l(-1), P < 0.05] and insulin concentrations [11.9 (0.9) vs 21.8 (1.8) mU x l(-1)] were lower. The 1-h post-exercise excess of VO2 [9.1 (0.25) vs 10.6 (0.25) 1, P < 0.05], and blood LA measured 3 min after the exercise [9.5 (0.4) vs 10.6 (0.5) mmol x l(-1), P < 0.05] were lower following the L-CHO treatment, whilst plasma NA and A concentrations reached higher values [2.24 (0.40) vs 1.21 (0.13) nmol x l(-1) and 14.30 (1.41) vs 8.20 (1.31) nmol x l(-1), P < 0.01, respectively]. In subjects on the L-CHO diet, the plasma beta-HB concentration decreased quickly after exercise, attaining approximately 30% of the pre-exercise value within 60 min, while insulin and glucose levels were elevated. The main conclusions of this study are: (1) a L-CHO diet is detrimental to anaerobic work capacity, possibly because of a reduced muscle glycogen store and decreased rate of glycolysis; (2) reduced carbohydrate intake for 3 days enhances activity of the sympathoadrenal system at rest and after exercise.

3-Hydroxybutyric Acid↗
PubMed1997

Physiological characteristics and hormonal profile of young normotensive men with exaggerated blood pressure response to exercise.

Exaggerated blood pressure (BP) response to exercise in normotensive subjects is considered as a predictor of future hypertension. The aim of the study was to find out whether elevated BP response to exercise is associated with any other haemodynamic, metabolic or hormonal abnormalities. Abnormal BP response to exercise, i.e. systolic BP (SBP) > 200 mmHg at 150 W or lower workload, was found in 37 out of 180 normotensive, male students, aged 20-24 years. Fifteen students with elevated exercise BP (group E) volunteered for further examinations. Their resting and ambulatory BP showed high normal values. Eight of them had a family history of hypertension. Four subjects met the criteria of cardiac hypertrophy. Significant correlations were found between exercise SBP and left ventricular mass index, average 24 h and daytime SBP recordings. In comparison with normal subjects of the same age (group N, n = 13), those from group E did not differ in body mass index, plasma lipid profile, fasting glucose, insulin and catecholamine (CA) concentrations, but had increased erythrocyte sodium content, slightly elevated plasma renin activity and cortisol level. During exercise, E subjects showed greater cardiac output (CO) increases with normal heart rate, total peripheral resistance (TPR) and plasma CA. There were no significant differences between groups in haemodynamic and plasma CA responses to posture change from supine to standing. Glucose ingestion (75 g) caused smaller increases in CO and smaller decreases in TPR in E than in N subjects without differences in BP, blood glucose plasma insulin and CA. It is concluded that young normotensive men with exaggerated BP response to exercise show some other characteristics that may be considered as markers of predisposition to hypertension or factors promoting the development of hypertension.

Adult↗
PubMed1996

Threshold increases in plasma growth hormone in relation to plasma catecholamine and blood lactate concentrations during progressive exercise in endurance-trained athletes.

Plasma human growth hormone ([HGH]), adrenaline ([A]), noradrenaline ([NA]) and blood lactate ([La-](b)) concentrations were measured during progressive, multistage exercise on a cycle ergometer in 12 endurance-trained athletes [aged 32.0 (SEM 2.0) years]. Exercise intensities (3 min each) were increased by 50 W until the subjects felt exhausted. Venous blood samples were taken after each intensity. The [HGH] and catecholamine concentrations increased negligibly during exercise of low to moderate intensities revealing an abrupt rise at the load corresponding to the lactate threshold ([La-]-T). Close correlations (P <0.001) were found between [La-]b and plasma [HGH] (r = 0.64), [A] (r = 0.71) and [NA] (r = 0.81). The mean threshold exercise intensities for [HGH], [A] and [NA], detected by log-log transformation, [154 (SEM 19) W, 162 (SEM 15) W and 160 (SEM 17) W, respectively] were not significantly different from the [La-]-T [161 (SEM 12) W]. The results indicated that the threshold rise in plasma [HGH] followed the patterns of plasma catecholamine and blood lactate accumulation during progressive exercise in the endurance-trained athletes.

Adult↗
PubMed1996

Effect of sustained hyperadrenalinemia on exercise performance and lactate threshold in rats.

The effect of prolonged elevation of blood adrenaline concentration (sustained up to 60 h) on exercise performance and lactate threshold (TLA) was investigated in 24 rats on the basis of a incremental, multistage treadmill exercise test, performed before and after subcutaneous implantation of retard adrenaline tablets (15 mg), which release adrenaline at a constant rate of approx. 1.6 micrograms min-1. Blood samples for lactate (LA) determinations were taken from the rats' tails after each exercise stage. The results obtained indicate that hyperadrenalinemia within the physiologic range, sustained for 6 or 12 h, decreases exercise performance, measured as the maximal speed of running, increases blood LA concentration during submaximal and maximal exercise, and shifts TLA toward lower exercise intensities than in control or sham-operated rats. When adrenaline excess was maintained for 60 h the maximal running speed was still reduced, and exercise blood LA was even higher than during earlier stages of hyperadrenalinemia, but TLA returned to control values. In the rat, a moderate excess of circulating adrenaline, sustained up to 60 h, reduces maximal exercise performance, and causes marked elevations in submaximal and maximal blood lactate concentration. However, this is accompanied by lowering of TLA only in the early stages of hyperadrenalinemia (6 and 12 h), which suggests that shifts of TLA may occur independently of absolute levels of blood lactate during graded exercise.

Animals↗
PubMed1996

Triacylglycerol synthesis in the different skeletal muscle fiber sections of the rat.

Triacylglycerol (TG) synthesis rates of low-oxidative fast-twitch white and high-oxidative fast- and slow-twitch red skeletal muscle fiber sections of adult rats were measured by the incorporation of perfusate-derived palmitate into the neutral lipid fraction by use of a perfused hindquarter preparation under high-flow conditions. The perfusion medium consisted of 95% O2-5% CO2 Krebs-Henseleit buffer, pH 7.4, containing 5 g/100 ml bovine serum albumin, 100 microU/ml insulin, 5 mmol/l glucose, amino acids, and added fatty acids (FA), including 0.1 microCi/ml [3H]palmitate. FA incorporation was linear with time. TG synthesis rates correlated (r > or = 0.90) with the oxidative capacity of each of the different fiber type sections and increased in proportion to the perfusate FA concentration (0.25, 0.5, 1.0, 1.5, and 2.0 mmol/l). TG synthesis rates among different muscle fiber sections were related (r > or = 0.90) to perfusate flow during high-flow conditions; however, this was not causal, because TG synthesis rates within each muscle fiber section were independent of flow rate when experimentally varied over an approximately threefold range. Thus the relatively high TG synthesis rates observed in the high-oxidative muscle sections are not uniquely related to their high-flow capacities but are inherent to the TG synthesis process, probably events associated with FA uptake and/or capacity of the TG synthesis pathway.

Animals↗
PubMed1996

Effect of low-carbohydrate-ketogenic diet on metabolic and hormonal responses to graded exercise in men.

Maximal oxygen uptake (VO2 max) and lactate threshold (LT) were measured during graded, incremental exercise in 8 healthy, untrained volunteers (aged 22 +/- 0.9 yrs) following 3 days on a control, mixed diet, or a ketogenic (50% fat, 45% protein and 5% carbohydrates) diet of equal energy content. Before and after exercise tests acid base balance, plasma beta-hydroxybutyrate (beta-HB), free fatty acid (FFA), and some hormone concentrations were determined. In comparison with the normal diet, the ketogenic diet resulted in: an increased VO2 max, decreased respiratory exchange ratio an a shift of LT towards higher exercise loads. Blood LA concentrations were lower before, during and after exercise. Post exercise blood pH, as well as pre-and post exercise base excess and bicarbonates were reduced. Resting beta-HB concentration was elevated to approx. 2.0 mM, and FFA to approx. 1.0 mM. During a 1 h recovery period beta-HB decreased to 0.85 mM (p < 0.01) after the ketogenic diet, while plasma FFA did not change after exercise under either conditions. Both the pre-and post-exercise levels of adrenaline, noradrenaline, and cortisol were enhanced, whilst plasma insulin concentration was decreased on the ketogenic diet. It is concluded that the short-term ketogenic diet does not impair aerobic exercise capacity, as indicated by elevated VO2 max and LT. This may be due to increased utilization of beta-HB and FFA when carbohydrate stores are diminished. Stimulation of the sympatho-adrenal system, and cortisol secretion with reduced plasma insulin concentration seem to be of importance for preservation of working capacity.

3-Hydroxybutyric Acid↗
PubMed1996

Phosphate supplementation prevents a decrease of triiodothyronine and increases resting metabolic rate during low energy diet.

Thirty overweight women participated in 8 week slimming program consisting of a self-controlled low-energy diet (4.2 MJ/day) supplemented with highly viscous fibres and mineral tablets containing calcium, potassium and sodium phosphates (Redusan Combi, Biokraft Pharma AB, Sweden). Half of the patients received in double blind manner mineral tablets during first 4 weeks and placebo (without phosphates) during next 4 weeks (group 1) while the remaining patients were treated (cross-over) with placebo first and mineral tablets in the final period (group 2). The rate of weight loss was similar in groups 1 and 2 (4.7 vs 5.2 kg during the first 4 weeks and 2.7 vs 3.0 kg in the further 4 weeks). During periods of phosphate supplementation, the resting metabolic rate (RMR) increased by approx. 12% (p < 0.05) in group 1 and 19% (p < 0.05) in group 2. Phosphate supplementation ameliorated also a decrease in plasma triiodothyronine level and a decrease in thyroxine to triiodothyronine ratio. There were no differences between groups in the plasma insulin, catecholamine, growth hormone, cortisol and testosterone levels. Phosphate supplementation did not affect plasma lipids or blood glucose concentration. It is concluded that phosphate supplementation in obese patients on a low-energy diet enhances RMR irrespectively of the rate of weight loss. This effect seems to be, at least partly, due to an influence of phosphates on peripheral metabolism of thyroid hormones.

Adult↗
PubMed1996

Influence of thyroid hormones on exercise tolerance and lactate threshold in rats.

Effects of thyroid hormone deficit, and triiodothyronine (T3) treatment on exercise performance, blood lactate (LA) concentrations and LA threshold (TLA) were studied in trained and untrained rats. Fourteen rats were thyroidectomized and then treated with propylthiouracil for 30 days (THY + PTU group). Fourteen sham operated rats served as controls. In each group there were 7 sedentary and 7 endurance-trained animals. Six weeks after thyroidectomy or sham operation the rats were subjected to a multistage running test with speed increasing from 13 m/min at 10 degrees treadmill inclination till maximum. Blood samples for LA were taken from the rats' tail after each 3-min exercise stage. During 3 days following this test rats from all groups were injected (i.p.) with 75 micrograms/100 g of triiodothyronine (T3), and 24 hrs afterwards the second exercise test was performed. In THY + PTU rats maximal running speed (RSmax) and the speed at which TLA occurred were markedly decreased in comparison with control group. The level of LA at the maximal speed (LAmax) and that corresponding to TLA were higher in THY + PTU rats than in controls. T3 injection to control animals diminished their RSmax and TLA, whereas in THY + PTU rats it increased RSmax and shifted TLA to a higher speed. Both in THY + PTU and control animals T3 elevated LAmax and the threshold LA concentration. Endurance training in control and THY + PTU animals markedly enhanced RSmax and TLA. This was accompanied by increases in LAmax and concentration of LA at TLA only in control group. After T3 injection to control trained rats RSmax and TLA were diminished, whereas in THY + PTU trained group RSmax was unchanged and TLA was elevated. Maximal blood LA increased only in THY + PTU trained rats whilst the threshold blood LA was elevated in both groups. It is concluded, that both the T3 deficiency and its excess reduce maximal exercise performance and shift TLA to lower workloads. Enduarance training or administration of T3 to hypothyroid rats markedly improve their exercise performance and elevate TLA, however, T3 treatment markedly increases maximal and submaximal LA levels.

Animals↗
PubMed1995

Low ambient temperature and neuroendocrine response to hypoglycemia in men.

Nutritional factors, such as an excess or a deficiency of glucose, play an important role in neuroendocrine regulations. Hormonal and metabolic responses to hypoglycemia were examined in healthy non-obese volunteers under conditions of low ambient temperature. Hypoglycemia was induced by intravenous injection of insulin in two randomized trials performed at room temperature and at 4 degrees C. At room temperature, the typical neuroendocrine response to hypoglycemia was established. The increases of ACTH, beta-endorphin, growth hormone and cortisol in response to insulin hypoglycemia failed to be modified by low ambient temperature. Acute cold exposure significantly reduced epinephrine and totally inhibited prolactin response to insulin-induced hypoglycemia. In spite of significant changes in epinephrine response to hypoglycemia at low ambient temperature, no striking differences in plasma glucose levels compared to those measured at room temperature were observed. However, under conditions of low temperature the reestablishment of normoglycemia was delayed. No changes in free fatty acids were found under our experimental conditions. The presented data show that low ambient temperature exerts selective effects on some neuroendocrine and metabolic parameters.

Adrenocorticotropic Hormone↗