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Biomedical subjects

H A Keizer

Publications and source records attributed to H A Keizer.

67 records · Page 4Linked to original sources
PubMed1987

Multiple hormonal responses to physical exercise in eumenorrheic trained and untrained women.

The aim of the present investigation was to compare the changes in plasma estradiol (E2), progesterone (P), luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone (T), androstenedione (delta 4-A), dehydroepiandrosterone sulfate (DHEA-S), adrenocorticotropic hormone (ACTH), and prolactin (PRL) in standardized tests (15-min consecutive work loads of 60%, 70%, 80% VO2 max to exhaustion) in 13 eumenorrheic untrained (UT) and 8 highly trained women (MR). Blood was obtained 15 and 2 min before exercise and at the end of each work load or each 15 min period. The results showed a significant increase (0.05 greater than P less than 0.001, two-way ANOVA) in plasma E2 P, T delta 4-A, PRL, and ACTH both in UT and MR irrespective of the phase of the menstrual cycle. DHEA S levels increased significantly in the MR, but not in the UT, PRL and ACTH increased linearly with exercise in MR and nonlinearly in UT. In the latter group, only the 80% VO2 max work load was able to elicit significant increments in the plasma levels of these hormones. In the MR plasma T and delta 4-A levels increased relatively more pronounced (P less than 0.05) at comparable work loads and exercise times than in the UT. LH levels decreased with exercise both in the UT and MR, whereas FSH levels remained unchanged (MR) or decreased (UT). These findings suggest that during exercise the ovarian hormones are increased by more unspecific mechanisms such as a decreased metabolic clearance rate, whereas in the MR, adrenal secretion of androgens is enhanced.

Adrenal Cortex Hormones↗
PubMed1987

Exercise-induced changes in the percentage of free testosterone and estradiol in trained and untrained women.

We have studied the effect of exercise on the percentage of free plasma estradiol 17-beta (E2) and testosterone (T) in 13 untrained (UT) and 8 trained (marathon runners, MR) eumenorrheic women. All women performed a standardized bicycle ergometer (UT) or treadmill (MR) test in the follicular and luteal phases of their menstrual cycles (15-min consecutive work loads of 60%, 70%, and 80% VO2 max to exhaustion). Blood was drawn through an indwelling venous catheter at 15 and 2 min before and immediately after exercise. Free E2 and T was assayed by centrifugal ultrafiltration using undiluted plasma at 37 degrees C (basal samples) and 39 degrees C (exercise samples). Statistical analysis was performed by a two-tailed paired t test. In the UT, the basal percentage of free E2 was measured to be 1.55% +/- 0.24% (mean +/- SD) in the follicular phase and 1.62% +/- 0.32% in the luteal phase (differences NS). In the MR, these values were 1.22% +/- 0.25% and 1.25% +/- 0.12% for the follicular and luteal phases, respectively. The differences between the groups were not significant. Exercise did not provoke significant changes in free E2 in either of the groups. Constrastingly, exercise induced a significant (P less than 0.02) increase in the percentage of free T from 1.56% +/- 0.27% to 2.1% +/- 0.36% and from 1.6% +/- 0.27% to 2.12% +/- 0.33% in the UT in the follicular and luteal phases, respectively. In the MR, the free percentage of T increased from 1.04% +/- 0.39% to 1.6% +/-0.16% (follicular phase) and from 1.24% +/- 0.22% to 1.67% +/- 0.18% (P less than 0.02).

Adult↗
PubMed1987

Effect of a 3-month endurance training program on metabolic and multiple hormonal responses to exercise.

We have investigated the effect of a 3-month endurance training program (running and cycling) on plasma hormone responses during standardized bicycle ergometer work (15-min consecutive work loads of 60%, 70%, 80%, and eventually 90% VO2 max) in eight previously untrained eumenorrheic women. The subjects were investigated before and after training both in the follicular and luteal phases of the menstrual cycle (between the 7th-10th and 20th-25th days of their menstrual cycle, respectively). Blood was obtained 15 and 2 min before the onset of exercise and at the end of each work load from an indwelling catheter. In each sample, the plasma concentrations of estradiol 17 beta (E2), progesterone (P), testosterone (T), androstenedione (delta 4-A), dehydroepiandrosterone sulfate (DHEA-S), prolactin (PRL), and adrenocorticotropic hormone (ACTH) were assayed in duplicate by RIA; lactate was assayed as well. The hormone concentrations were expressed in absolute as well as in relative values. After training basal DHEA-S and ACTH levels were significantly (P less than 0.05) lower in both phases of the menstrual cycle, whereas basal luteal phase E2 and T levels were significantly (0.05 greater than P greater than 0.01) lower after training. Exercise induced significant increments in the relative values of all hormones in both phases (0.05 greater than P greater than 0.001). After training, T and DHEA-S increased relatively more pronounced (0.05 greater than P greater than 0.02) in the follicular and luteal phase, respectively.

Adrenal Cortex Hormones↗
PubMed1987

Pituitary, ovarian, and adrenal hormone responses to marathon running.

We have described the responses of selected hormones [luteinizing hormone (LH), follicle-stimulating hormone (FSH), estradiol (E2), progesterone (P), androstenedione (delta 4-A), testosterone (T)] and substrates (glucose, lactate) before, during, and after a marathon run in five women of varying gynecological status. Blood samples (15 ml) were obtained 60 and 30 min before the race, during the race at 10, 20, and 30 km, and after the race at min 5, 60, and 120. The relative intensity of running varied between 60% and 85% VO2 max, and weight loss ranged from 2.6 to 3.0 kg. The new observations from our data include the fact that FSH was increased during exercise, whereas this was not observed for LH. This latter hormone appears to be linked more closely to the exercise intensity as defined by blood lactate increments. Increments occurred in all steroid hormones and paralleled those observed in controlled laboratory studies, although the magnitude of these changes was larger at the end of the marathon run. Except for dehydroepiandrosterone sulfate (DHEA-S), most of the hormones returned to basal levels in the 2 h after the marathon. DHEA-S exhibited no change until the 30-km point, when a sharp increase was observed, and then remained elevated for 2 h after exercise, suggesting that a) adrenocortical production of steroids continues for a long time after exercise, b) there is a marked reduction in hepatic clearance of this hormone. In summary, the present study shows that prolonged exercise has a marked effect on both steroid and pituitary hormones.

Adrenal Cortex Hormones↗
PubMed1985

Variability of aerobic performance in the laboratory and its physiologic correlates.

To study the physiologic basis of variability of physical performance in the laboratory, ten male subjects were studied once a week, during a 9-12 month period. Previously, the reference maximal work load attained (Wref) was determined in each subject. The test protocol of the actual study was based on the individual Wref and started at 70% Wref for 5 min whereupon the work load was increased by 5% Wref every 2.5 min to exhaustion. The maximal work load attained (Wmax) was considered as the test performance. Heart rate, respiratory variables, oxygen uptake (VO2), and blood lactate concentration were determined at each work load. The rate of perceived exertion during submaximal and maximal work was also scored. In all subjects, Wmax and VO2max varied randomly, while the coefficient of variation in VO2max (4.20% - 11.35%) exceeded that in Wmax (2.95%-6.83%). No seasonal influences on VO2 max and Wmax were observed. In all subjects the physiologic variables, when plotted as a function of external work load, were shifted to the right with higher Wmax values and to the left with lower Wmax values. With lower Wmax values, the rate of perceived exertion during submaximal work tended to increase. The results suggest that the magnitude of physiologic responses to exercise is related to relative work load and that variability of physical performance is related to changes in gross mechanical efficiency.

Adult↗
PubMed1985

Influence of a prostaglandin-inhibiting drug on muscle soreness after eccentric work.

Since the time sequence of exercise-induced muscle soreness corresponds well with the time sequence of exercise-induced morphological changes in animal skeletal muscle, it has been suggested that muscle soreness is related to an inflammatory response. Prostaglandins are assumed to play a role in the inflammatory process. The influence of a cyclo-oxygenase-inhibiting drug (flurbiprofen) on the subjective symptoms of soreness and eventual structural changes was investigated in six male subjects. The subjects performed one concentric and two eccentric work bouts of 30 min at 80% of the individual maximal work load on the bicycle ergometer. Muscle biopsies taken before, immediately after, and 24 h after work were used to examine structural, ultrastructural changes as well as for assessment of glycogen content. Plasma levels of muscle enzymes and subjective soreness were determined at regular intervals. Eccentric work elicited muscle soreness in all subjects: however, the soreness was consistently less in the second eccentric trial. No significant enzyme release was noticed in any of the subjects, whereas ultrastructural changes were restricted to the mitochondria. No influence of flurbiprofen on subjective soreness was noticed. After both eccentric trials muscle glycogen was lower 24 h after work compared to the content immediately after work. The results suggest that eccentric exercise interferes with glycogen synthesis and that prostaglandins do not play a major role in exercise-induced muscle soreness.

Adult↗
PubMed1983

The effect of some sex hormones on the isovolumetric pressure curve of the rabbit's left ventricle.

The effect of some sex hormones (estradiol-17 alpha), estradiol-17 beta, estrone, progesterone and testosterone) on the mechanical activity of rabbit left ventricle was studied in concentrations within the physiological range. Investigations were carried out during the first ten minutes after the introduction of the steroid. Only progesterone and estradiol-17 beta affect the isovolumetric pressure curve; the other steroids do not exhibit any effect. The effects of estradiol-17 beta and progesterone counterbalance each other. Estradiol-17 beta enhances the rate of pressure development and decreases the time to reach peak pressure. Progesterone decreases both the rate of pressure development and the time to reach peak pressure.

Animals↗
PubMed1982

Direct action of estradiol-17 beta on the atrial action potential.

The effect of the two C-17 isomers of estradiol on the shape of the action potential of rat atrial tissue was studied by means of classical glass electrodes for different concentrations of estradiol. Resting potential and upstroke were not affected by estradiol, but the duration of the action potential was reduced. Only estradiol-17 beta exhibits an effect in a concentration dependent way, while estradiol-17 alpha has no effect at all. The ionic mechanism was studied by adding specific ionic blockers to the perfusate. Since the effect was much less pronounced when a slow inward current blocker was added, it was concluded that estradiol-17 beta acts mainly via the slow inward current channel. Only a small part of the interaction takes place via the potassium outward channel.

Action Potentials↗
PubMed1982

Limitations of concentration measurements for evaluation of endocrine status of exercising women.

The impact of changes in metabolic clearance rates (MCR), biologic activity of sex-steroids, steroid-protein interaction and steroid-binding properties of plasma proteins in relation to physical exercise are reviewed. The MCR of estradiol is decreased during physical exercise but this phenomenon is only partly explained by a decreased hepatic blood flow. Changes in concentration of high-affinity steroid binding proteins (testosterone-estradiol-binding globulin, TeBG) affect predominantly the amount of free testosterone (T) and its MCR. During exercise both the lower sex-steroids binding affinities of plasma proteins due to increased body temperature and the increased concentration of these hormones cause a shift towards an increased free concentration. Due to competitive interactions between androgens and estrogens for the binding site of TeBG the free concentration of estrogens will probably increase more than expected. The physiological meaning of these changes are discussed.

Adolescent↗
PubMed1980

Influence of physical exercise on sex-hormone metabolism.

We have studied the effects of short-term exercise on the degradation rate of estradiol (E2) measured as the metabolic clearance rate (MCRE2). Six young women (mean age 20.7 yr) volunteered for this study in which we investigated the influence of a submaximal bicycle ergometer load on the MCRE2. All measurements were done in the morning of the 7th to 10th day of the menstrual cycle. [3H]estradiol 17 beta ([3H]E2) was administered intravenously at a constant rate by an infusion pump. During the exercise period on the bicycle ergometer (70% VO2max, 10 min) and the recovery period (25% VO2max, 30 min), several blood samples were taken in which the [3H]E2 concentration was estimated. The results showed a strong decrease in the MCRE2 (range 18-67%) at the end of the work load for all the volunteers. At the end of the recovery period, the MCR was still lower than the basal value (range 30-50%). The possible mechanisms and relevance of these exercise-induced MCR changes of estradiol are discussed.

Adult↗
PubMedDate not supplied

Physiological, biochemical and psychological markers of strenuous training-induced fatigue.

The purpose of the study was to investigate whether severe fatigue, possibly leading to overreaching, could be diagnosed at an early stage by a combination of parameters. Seven well-trained male subjects (age [mean +/- SD]: 25.3 +/- 4.7 yr; body mass: 76 +/- 6.6 kg; VO2max: 61.1 +/- 7 ml.kg(-1).min(-1)) increased their training load by doubling their training volume and increasing the intensity by 15 % over a period of two weeks. Before and after this intensified training period subjects underwent a series of tests including a maximal incremental cycle ergometer test (Wmax) with continuous ventilatory measurements and blood lactate values, time trial, basal blood parameter tests (red and white blood profile), hormones [growth hormone (GH), insulin-like growth factor 1(IGF-1), adreno-corticotropic hormone (ACTH), cortisol], neuro-endocrine stress test [short insulin tolerance test (SITT), combined anterior pituitary test (CAPT) and exercise], a shortened Profile of Mood State (POMS), the estimated rate of perceived exertion (RPE) and a cognitive reaction time test. The intensified training period resulted in a significant increase of the training load (p <0.01), training monotony (p <0.01) and training strain (p <0.01). The RPE during training increased significantly (p <0.01) during the intensified training period. Total mood score obtained from the POMS tended to increase (p=0.06), reflecting an increase in worse mood state. A novel finding was that reaction times increased significantly, indicating that overreaching might adversely affect speed of information processing by the brain, especially for the most difficult conditions. After the intensified training period, neither changes in exercise-induced plasma hormone values, nor SITT values were observed. During the CAPT only cortisol showed a significant decrease after the intensified training period. Hemoglobin showed a significant decrease after the intensified training period whereas hematocrit, red blood cell count (RBC) and MCV tended to decrease. The intensified training had no effect on physical performance (Wmax or time trial), maximal blood lactate, maximal heart rate and white blood cell profile. The most sensitive parameters for detecting overreaching are reaction time performance (indicative for cognitive brain functioning), RPE and to a lesser extend the shortened POMS. This strongly suggests, that central fatigue precedes peripheral fatigue. All other systems,including the neuro-endocrine, are more robust and react most likely at a later stage in exhaustive training periods.

Adult↗