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Biomedical subjects

B Kruk

Publications and source records attributed to B Kruk.

At least 19 recordsLinked to original sources
PubMed1992

Metabolic, body temperature and hormonal responses to repeated periods of prolonged cycle-ergometer exercise in men.

This study was designed to find out whether rest intervals and prevention of dehydration during prolonged exercise inhibit a drift in metabolic rate, body temperature and hormonal response typically occurring during continuous work. For this purpose in ten healthy men the heart rate (fc), rectal temperature (Tre), oxygen uptake (VO2), as well as blood metabolite and some hormone concentrations were measured during 2-h exercise at approximately 50% maximal oxygen uptake split into four equal parts by 30-min rest intervals during which body water losses were replaced. During each 30-min exercise period there was a rapid change in Tre and fc superimposed on which, these values increased progressively in consecutive exercise periods (slow drift). The VO2 showed similar changes but there were no significant differences in the respiratory exchange ratio, pulmonary ventilation, mechanical efficiency and plasma osmolality between successive periods of exercise. Blood glucose, insulin and C-peptide concentrations decreased in consecutive exercise periods, whereas plasma free fatty acid, glycerol, catecholamine, growth hormone and glucagon concentrations increased. Blood lactate concentrations did not show any regular drift and the plasma cortisol concentration decreased during the first two exercise periods and then increased. In conclusion, in spite of the relatively long rest intervals between the periods of prolonged exercise and the prevention of dehydration several physiological and hormonal variables showed a distinct drift with time. It is suggested that the slow drift in metabolic rate could have been attributable in the main to the increased concentrations of heat liberating hormones.

Adult↗
PubMed1991

Comparison in men of physiological responses to exercise of increasing intensity at low and moderate ambient temperatures.

In six male subjects the sweating thresholds, heart rate (fc), as well as the metabolic responses to exercise of different intensities [40%, 60% and 80% maximal oxygen uptake (VO2max)], were compared at ambient temperatures (Ta) of 5 degrees C (LT) and 24 degrees C (MT). Each period of exercise was preceded by a rest period at the same temperature. In LT experiments, the subjects rested until shivering occurred and in MT experiments the rest period was made to be of exactly equivalent length. Oxygen uptake (VO2) at the end of each rest period was higher in LT than MT (P less than 0.05). During 20-min exercise at 40% VO2max performed in the cold no sweating was recorded, while at higher exercise intensities sweating occurred at similar rectal temperatures (Tre) but at lower mean skin (Tsk) and mean body temperatures (Tb) in LT than MT experiments (P less than 0.001). The exercise induced VO2 increase was greater only at the end of the light (40% VO2max) exercise in the cold in comparison with MT (P less than 0.001). Both fc and blood lactate concentration [1a]b were lower at the end of LT than MT for moderate (60% VO2max) and heavy (80% VO2max) exercises. It was concluded that the sweating threshold during exercise in the cold environment had shifted towards lower Tb and Tsk. It was also found that subjects exposed to cold possessed a potentially greater ability to exercise at moderate and high intensities than those at 24 degrees C since the increases in Tre, fc and [1a]b were lower at the lower Ta.

Adolescent↗
PubMed1990

Thermoregulatory responses to exercise at low ambient temperature performed after precooling or preheating procedures.

Seven male skiers exercised for 30 min on a cycle ergometer at 50% of maximal oxygen uptake and an ambient temperature of 5 degrees C. The exercise was preceded either by cold exposure (PREC) or active warming-up (PREH). The data were compared with control exercise (CONT) performed immediately after entering the thermal chamber from a thermoneutral environment. Cold exposure resulted in negative heat storage (96.1 kJ.m-2, SE 5.9) leading to significantly lower rectal, mean body and mean skin temperatures at the onset of exercise in PREC, as compared to PREH and CONT. The PREC-PREH temperature differences were still significant at the end of the exercise period. During exercise in the PREC test, oxygen uptake was higher than in PREH test (32.8 ml.kg-1.min-1, SE 1.5 vs 30.5 ml.kg-1.min-1, SE 1.3, respectively). Heart rate showed only a tendency to be higher in PREC than in PREH and CONT tests. In the PREH test skin and body temperatures as well as sweat rate were already elevated at the beginning of exercise. Exercise-induced changes in these variables were minimal. Heat storage decreased with the duration of the exercise. Exercise at low ambient temperature preceded by a 30-min rest in a cold environment requires more energy than the same exercise performed after PREH.

Adolescent↗
PubMed1988

Thyroid hormone deficiency and muscle metabolism during light and heavy exercise in dogs.

Muscle glycogen, glycolytic intermediate and high energy phosphate contents were compared in 5 intact-control (C) and thyroidectomized (THY) dogs after 30 min treadmill exercise of low (40W) and high (70W) intensities. Although after the exercise of relatively low intensity the rate of glycogenolysis and muscle lactate accumulation in THY dogs exceeded those in controls, the diminished oxidative capacity in the former was inadequately compensated, resulting in lowering of APT and CrP contents. At the higher work load the latter effects were more pronounced while the rate of glycogenolysis was similar or even lower than in controls. Inadequate fuel utilization may be considered as a factor limiting ability for heavy exercise in hypothyroidism.

Adenosine Triphosphate↗
PubMed1988

Thyroid hormones and muscle metabolism in dogs.

Muscle contents of ATP, ADP, AMP, creatine phosphate and creatine as well as glycogen, some glycolytic intermediates, pyruvate and lactate were compared in the intact, thyroidectomized and triiodothyronine (T3) treated dogs under resting conditions. After thyroidectomy muscle glycogen, glucose 1-phosphate and glucose 6-phosphate contents were significantly elevated while in T3-treated animals these variables were decreased in comparison with control dogs. Muscle free glucose was not altered by thyroidectomy but T3 treatment significantly increased its content. Muscle lactate content was elevated both in hypo- and hyperthyroid animals. Muscle ATP and total adenine nucleotide contents were significantly increased in hyperthyroid dogs while no differences were found between the three groups in the muscle creatine phosphate content. It is assumed that in T3-treated animals carbohydrate catabolism is enhanced in the resting skeletal muscle in spite of high tissue ATP content. Muscle metabolite alterations in hypothyroid dogs seem to reflect the hypometabolism accompanied by a diminished rate of glycogenolysis with inhibited rate of pyruvate oxidation or decreased rate of lactate removal from the cells.

Adenine Nucleotides↗
PubMed1987

Enhanced glucose availability for working muscles reduces exercise hyperthermia in dogs.

Body temperature and metabolic responses to 2 h treadmill exercise in dogs given glucose intravenously (25-30 mg.kg-1 X min-1 throughout the run) were compared with those measured in the same animals with elevated plasma FFA concentrations (soya bean oil ingestion + intravenous heparin) and in control experiments (24 h fasting). In comparison with control conditions enhanced glucose availability for the working muscles caused a reduction in the exercise-induced increases in both rectal (by 0.9 +/- 0.11 degree C) and muscle (by 0.9 +/- 0.16 degree C) temperatures, a lower rate of oxygen uptake (by 16%) and an elevated respiratory exchange ratio. A tendency towards enhanced body temperature responses to exercise, accompanied by increases in VO2 and cardiac frequency was noted in dogs with elevated plasma FFA concentrations as compared with the control animals. The estimated amount of heat effectively dissipated from the body, expressed as a fraction of heat load (thermoregulatory efficiency) was significantly higher in dogs infused with glucose (0.962 +/- 0.0035), than in the controls (0.947 +/- 0.0043) and those with elevated plasma FFA concentrations (0.931 +/- 0.0029). It is concluded that the increased contribution of carbohydrates to the energy yield during exercise results in a marked attenuation of hyperthermia, associated with a reduced metabolic rate and improved thermoregulatory efficiency.

Animals↗
PubMed1985

Hypothalamic, rectal, and muscle temperatures in exercising dogs: effect of cooling.

To investigate mechanisms that may be involved in the prolongation of exercise performance with body cooling hypothalamic (Thy), rectal (Tre), and exercising muscle (Tm) temperatures, as well as the heart rate, respiratory rate, blood lactic acid concentration ( [LA] ), and plasma osmolality (Osm) were measured in five dogs during exhaustive treadmill exercise at an ambient temperature (Ta) of 22 +/- 1 degree C without cooling (control) and with external cooling by use of ice packs. In both series of experiments, dehydration of animals was prevented. Compared with exercise with noncooling, exercise with cooling resulted in 1) increased exercise duration from 90 +/- 14 to 145 +/- 15 min (62%, P less than 0.05); 2) attenuated increases in Thy, Tre, and Tm; 3) decreased respiratory and heart rates; and 4) lowered LA. Significant negative correlations were found between both Tm and delta Tm attained at 60 min of the run and time of exercise until exhaustion (r = -0.72 and -0.74, respectively; P less than 0.02). This work failed to differentiate clearly changes or equilibrium levels of brain, core, or muscle temperature as separate factors affecting work tolerance. However, the inverse relationship between Tm reached at 60 min of the run (in both experiments) and the total duration of exercise indicates that sustained muscle hyperthermia may largely contribute to limitation of working ability.

Animals↗
PubMed1985

Exercise hyperthermia as a factor limiting physical performance: temperature effect on muscle metabolism.

The muscle contents of high-energy phosphates and their derivatives [ATP, ADP, AMP, creatine phosphate (CrP), and creatine], glycogen, some glycolytic intermediates, pyruvate, and lactate were compared in 11 dogs performing prolonged heavy exercise until exhaustion (at ambient temperature 20.0 +/- 1.0 degrees C) without and with trunk cooling using ice packs. Without cooling, dogs were able to run for 57 +/- 8 min, and their rectal (Tre) and muscle (Tm) temperatures increased to 41.8 +/- 0.2 and 43.0 +/- 0.2 degrees C, respectively. Compared with noncooling, duration of exercise with cooling was longer by approximately 45% while Tre and Tm at the time corresponding to the end of exercise without cooling were lower by 1.1 +/- 0.2 and 1.2 +/- 0.2 degrees C, respectively. The muscle contents of high-energy phosphates (ATP + CrP) decreased less, the rate of glycogen depletion was lower, and the increases in the contents of AMP, pyruvate, and lactate as well as in the muscle-to-blood lactate ratio were smaller. The muscle content of lactate was positively correlated with Tm. The data indicate that with higher body temperature equilibrium between high-energy phosphate breakdown and resynthesis was shifted to the lower values of ATP and CrP and glycolysis was accelerated. The results suggest that hyperthermia developing during prolonged muscular work exerts an adverse effect on muscle metabolism that may be relevant to limitation of endurance.

Adenine Nucleotides↗
PubMed1983

Reduced hypothalamic thermosensitivity following intraventricular injection of pyrogen in conscious rabbits.

Hypothalamic temperature thresholds for vasodilatory and respiratory reactions were determined before and after i.c.v. injection of pyrogen in rabbits. During the rising phase of fever the increases in the hypothalamic thresholds for vasodilatory and respiratory reactions differed from those found in the pre-pyrogen preoptic anterior hypothalamic area (POAH) heating by 2.1 +/- 0.2 degrees C and 1.89 +/- 0.31 degrees C, respectively. During the plateau phase of fever the threshold for vasodilatory reaction was further increased (by 0.7 +/- 0.23 degrees C), whereas that for panting remained at the same level. It is concluded that pyrogen exerts a depressive action on POAH thermosensitivity.

Animals↗
PubMed1978

Antidiuretic action of intravenous and intracerebral pyrogen in conscious rabbits.

1. In conscious rabbits an i.v. infusion of 30 or 60 microgram E. coli pyrogen/kg body wt. decreased urine flow from control of 1.13 +/- 0.11 (S.E. of mean) ml./min to 0.43 +/- 0.09 ml./min while urine osmolality increased from 212 +/- 16 to 679 +/- 82 m-osmole/kg H2O. Clearances of exogenous creatine and p-aminohippurate did not change significantly. 2. Plasma antidiuretic activity (rat bio-assay) increased from control of 15.5 +/- 4.2 to 56.8 +/- 5.5 muu./ml. at the top of antidiuresis. 3. Comparable urine flow and osmolality changes were evoked by a pyrogen dose of only 0.2 microgram per animal injected into the lateral cerebral ventricle. 4. The results suggest that in the rabbit pyrogen stimulates ADH release by an unknown central mechanism.

Animals↗
PubMed1978

[Amplification factor in the thermoregulatory system at different environmental temperatures].

With the aid of a heater implanted into the hypothalamus, the temperature was raised in the medial preoptic area of the rabbit hypothalamus; Vasodilatation was observed at that in the helix and in the nose skin. The heat emanated during this response was measured with the aid of a dynamic biocalorimeter. The amplification coefficient in the thermoregulation system was calculated as the ratio: the heat emanated by the rabbit during the vascular thermoregulatory response--the heat introduced into the hypothalamus in the course of heating. At the temperature 20% in the calorimeter chamber, the amplification coefficient was 3.9+/-0.8, and at 24 degrees it was as high as 13.6+/-1.0.

Animals↗
PubMed1977

Renal function changes during preoptic-anterior hypothalamic heating in the rabbit.

Thermoregulatory reactions evoked by selective preoptic-anterior hypothalamic (PO/AH) heating in conscious rabbits were associated with significant changes in renal function. Urine flow rate decreased from a control value of 0.92 +/- (S.E.) 0.08 to 0.47 +/- 0.07 ml/min after 10-20 min of heating, urine osmolality increased from 273 +/- 34 to 417 +/- 46 Osm/kg H2O, and free water clearance per 100 ml GFR decreased from 1.11 +/- 0.46 to -0.50 +/- 0.23 ml/min. These changes were followed by a gradual recovery despite continued heating. Clearances of exogenous creatinine and p-aminohippurate fell transiently during the first 10 min of heating and then returned to normal. Plasma antidiuretic activity (ADA) measured by rat bioassay increased regularly and markedly during PO/AH heating but was poorly correlated with changes in urine concentration. Moreover, a similar increase in plasma ADA observed with selective heating of a different brain area (supraoptic nucleus) never produced urine concentration or other renal changes. This suggests that a large and variable fraction of ADA appearing in rabbit blood in response to thermal stimuli was not identical with antidiuretic hormone. Therefore, the causal relationship of ADH release and antidiuresis associated with thermoregulatory reactions could not be clearly demonstrated. The physiological role of renal water conservation would be to compensate for extrarenal water loss related to thermal sweating or panting.

Animals↗
PubMed1972

Effects of emotional factors on physical performance of dogs on the treadmill.

In dogs exercising on a treadmill, increase of physical performance was particularly pronounced when the animals were punished by an electric shock for slowing the speed of running and also upon hypothalamic stimulation producing flight response. This was accompanied by alterations of autonomic and metabolic functions. Food and stimulation of hypothalamic self-stimulation areas used as a reward for better performance was also effective, but only at the beginning of the work. On the other hand, hypothalamic and midbrain stimulation which produced a passive fear response decreased the intensity of work. Autonomic and metabolic functions were strongly affected. It appears that both the animal's motor activity and vegetative processes may be influenced by motivational factors in the course of physical performance.

Animals↗
PubMedDate not supplied

Thermoregulatory and metabolic responses to repeated bouts of prolonged cycle-ergometer exercise in man.

Changes in body temperature, oxygen uptake (VO2), heart rate (HR), sweating rate and plasma osmolarity were examined in 10 human subjects, performing four successive 30 min exercise-bouts of the same intensity (50% VO2 max) separated by 30 min rest periods. In spite of the rest intervals and replacement of body fluid loss there was a progressive increase in VO2. HR, rectal (Tre) and mean body (Tb) temperatures in consecutive exercise bouts. The thermoregulatory efficiency showed an increasing tendency, and a delay in the sweating response at the beginning of each exercise was shortened. It is concluded that a drift in metabolic and temperature responses to exercise, reported throughout a long-term continuous work, occurs also in the euhydrated subjects performing a prolonged intermittent exercise. It is not caused by an impaired thermoregulation during exercise but rather by insufficient restitution of metabolic processes during rest intervals.

Adult↗
PubMedDate not supplied

Progressive enhancement of body temperature responses to consecutive exercise-bouts of the same intensity in dogs.

Progressive enhancement of body temperature responses to consecutive exercise-bouts of the same intensity in dogs. Acta physiol. pol., 1985, 36 (3): 165-174. Changes in rectal (Tre), muscle (Tm), and hypothalamic (Thy) temperatures, plasma osmolality, and some intermediary metabolic variables were examined in dogs performing four successive exercise-bouts of the same intensity. During the rest-intervals separating the exercise-bouts body temperatures returned to initial levels and water losses were replaced. Tm and Tre responses to consecutive exercise-bouts were progressively increasing. Similar tendency was found in Thy changes. Cardiac and respiratory frequencies attained the same levels in all four exercise-bouts, while blood lactate and FFA concentrations were increasing and blood glucose level was decreasing progressively. No changes in plasma osmolality was noted. Exercise-induced increases in Tm correlated positively with plasma FFA concentration (r = 0.68). Body temperature responses to exercise were reduced by beta-adrenergic blockade. It is concluded that the enhancement of the thermal responses to consecutive exercise-bouts can be related to the metabolic action of catecholamines.

Animals↗