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Query: UMLS:C0015672 (fatigue)
 51,768 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A 9-year-old boy who complained of fatigue, myalgias, and progressive weakness was found to have a markedly elevated serum creatine phosphokinase (CPK). He developed polyuria with polydipsia and was noted to be hypertensive and severely hypokalemic. Treatment with potassium and spironolactone alleviated his signs and symptoms and normalized the blood pressure and CPK. Initial studies revealed low plasma renin activity that did not increase with change from supine to upright position. Plasma aldosterone was consistently elevated in the supine position, decreased with upright posture, and was not suppressed by administration of dexamethasone. Plasma 18-hydroxycorticosterone also was elevated. Enhanced computerized tomography (CT) revealed a mass in the left adrenal that had not been seen on the initial unenhanced scan. Adrenal vein catheterization confirmed elevated plasma aldosterone on that side. Adrenalectomy was performed, and a well-encapsulated adenoma was found at examination of the surgical specimen. Postoperatively, suppression of plasma renin activity continued for many months without signs of aldosterone deficiency.
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PMID:Aldosterone-producing adenoma presenting with hypokalemic myopathy. Case report and review. 329 4

The contraceptive efficacy of gossypol was investigated in a double-blind, randomized, control study. 75 male volunteers were placed on a regimen of 20 mg of gossypol per day, while the 77 controls received a placebo. Each of the volunteers continued use of gossypol for at least 14 1/2 months. Of the 64 gossypol-treated participants who completed the study, 31% achieved azoospermia and 61% had a sperm count less than 4 x 10 6. A 92% efficacy rate was achieved at the end of the loading phase. Incidence rates for fatigue, decrease of libido, and appetite did not differ significantly between subjects and controls, nor were there any differences in terms of body weight, hemoglobin, serum potassium, or blood pressure. Efficacy rates of 87%, 97%, 95%, 92%, and 98% were achieved at the end of loading, 3, 6, 9, and 12 months of maintenance, respectively. The only significant side effect appeared to be a lowering of serum potassium levels during the maintenance phase. The attrition rate was 26% at 6 months and 39% at 12 months. There were no pregnancies among the wives of the volunteers. At present, gossypol research in China is aimed at the supplementation of gossypol contraception with potassium salt or with a potassium blocker to ameliorate gossypol-related hypokalemia.
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PMID:Clinical trial of gossypol as a male contraceptive drug. Part I. Efficacy study. 330 87

Findings from five separate studies of EMG changes and muscle fatigue during prolonged low-level static contractions are summarized, and the possible mechanisms behind the changes are briefly discussed. Sustained static contractions (10%, 7% and 5% MVC) of up to 1 h duration were performed by finger flexors, elbow flexors and extensors, and knee extensors. In one experiment, intermittent static arm pulling (triceps) (10 s contraction and 5 s rest, average work load 14% and 10% MVC) was performed for 7 h. The endurance time for the sustained contractions was around one hour for 10% MVC, and it was shown--all in all--that the concept of "indefinite" endurance times at contractions below 15-20% MVC cannot be maintained. After 5% MVC sustained contractions for one hour a 12% reduction in MVC was seen, and significant increases in EMG amplitude and decreases in the mean spectral frequency of the EMG-power spectrum were found. Marked differences were also seen in the EMG changes in the elbow flexors and extensors, and transcutaneous electrical stimulation of the knee extensors showed that low frequency fatigue was present after the contraction. With intermittent contractions similar changes in the EMG parameters were seen after 2-3 h of contractions at 14% MVC. On average, during contractions of 10% MVC no EMG changes were detected. Increased extracellular potassium concentration in the contracting muscles is suggested as a possible explanation of these findings.
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PMID:Electromyography and fatigue during prolonged, low-level static contractions. 337 40

The effect of isometric exercise on blood flow, blood pressure, intramuscular pressure as well as lactate and potassium efflux from exercising muscle was examined. The contractions performed were continuous or intermittent (5 s on, 5 s off) and varied between 5% and 50% maximal voluntary contraction (MVC). A knee-extensor and a hand-grip protocol were used. Evidence is presented that blood flow through the muscle is sufficient during low-level sustained contractions (less than 10% MVC). Despite this muscle fatigue occurs during prolonged contractions. One mechanism for this fatigue may be the disturbance of the potassium homeostasis. Such changes may also play a role in the development of fatigue during intermittent isometric contractions and even more so in the recovery from such exercise. In addition the role of impaired transport of substances within the muscle, due to long-lasting daily oedema formation, is discussed in relation to fatigue in highly repetitive, monotonous jobs.
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PMID:Muscle blood flow during isometric activity and its relation to muscle fatigue. 337 42

The characteristics of long-duration inhibitory postsynaptic potentials (1-IPSPs) which are evoked in rat frontal neocortical neurons by local electrical stimulation were investigated with intracellular recordings from an in vitro slice preparation. Stimulation with suprathreshold intensities evoked 1-IPSPs with typical durations of 600-900 msec at resting membrane potential. Conductance increases of 15-60% were measured at the peak amplitude of 1-IPSPs (150-250 msec poststimulus). The duration of the conductance increases during 1-IPSPs displayed a significant voltage dependence, decreasing as the membrane potential was depolarized and increasing with hyperpolarization. The reversal potential of 1-IPSPs is significantly altered by reductions in the extracellular potassium concentration. Therefore it is concluded that 1-IPSPs in rat neocortical neurons are generated by the activation of a potassium conductance. 1-IPSPs exhibit stimulation fatigue. Stimulation with a frequency of 1 Hz produces a complete fatigue of the conductance increases during 1-IPSPs after approximately 20 consecutive stimuli. Recovery from this fatigue requires minutes. 1-IPSPs are not blocked by bicuculline but are blocked by baclofen.
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PMID:Characteristics of long-duration inhibitory postsynaptic potentials in rat neocortical neurons in vitro. 359 15

Recently it has been demonstrated that the loss of water during aging from rat liver and heart muscle tissue is solely due to water loss from the mitochondria. A hypothesis is presented here which shows the relation between free radical attack to, and water loss from, the mitochondria and the decreased energy availability in aged cells. According to it, water loss from the mitochondria is due to an increasing permeability of the inner mitochondrial membrane as a result of its changed composition and, therefore, decreasing osmotic reflexion coefficients for inorganic ions, mainly potassium. The water loss results in limited diffusion of intramitochondrial metabolites and, according to the theory of polyelectrolyte solutions, electrostatic and sterical hindrance of enzymic functions. The hypothesis is in accordance with the well-documented experimental facts, e.g. the lack of structural alterations in mitochondrial DNA and proteins, the constancy of the delta mu H+ and the decrease of state 3 respiration with only a limited number of substrates in mitochondria from old postmitotic cells.
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PMID:A mitochondrial membrane hypothesis of aging. 369 44

Intracellular potassium ([K+]i), interstitial potassium ([K+]inter), intracellular sodium ([Na+]i), and resting membrane potential (RMP) were measured before and after repetitive stimulation of mouse soleus and EDL (extensor digitorum longus) muscles. At rest, RMP was -69.8 mV for soleus and -74.9 mV for EDL (37 degrees C). [K+]i was 168 mM and 182 mM, respectively. In soleus, free [Na+]i was 12.7 mM. After repetitive stimulation (960 stimuli) RMP had decreased by 11.9 mV for soleus and by 18.2 mV for EDL. [K+]i was reduced by 32 mM and 48 mM, respectively, whereas [K+]inter was doubled. In soleus [Na+]i had increased by 10.6 mM, demonstrating that the [K+]i-decrease is three times higher than the [Na+]i-increase. It is concluded that this difference reflects different activity induced movements of Na and K, and that the difference is not due to the Na/K pumping ratio. The possible involvement of the potassium loss in muscle fatigue is discussed. After stimulation RMP recovered with a time constant of 0.9 min for soleus and 1.5 min for EDL. Within the first minutes after stimulation the intracellular potassium concentration increased by 20.4 mM/min for soleus and 21.7 mM/min for EDL. Free [Na+]i decreased with less than 10 mM/min. The mechanisms underlying the different rate of changes are discussed.
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PMID:Potassium and sodium shifts during in vitro isometric muscle contraction, and the time course of the ion-gradient recovery. 371 46

Torasemide 40 mg/day p.o. was administered for 21 days to 8 healthy volunteers to investigate its pharmacodynamics, pharmacokinetics and safety on chronic administration. It induced a highly significant initial increase in 24-h urinary volume and 24-h excretion of sodium and chloride, but its affect diminished after the first days. On Days 0, 1, 10 and 21 the experiment was divided in 3 clearance phases, extending from 0 to 2 h, 2 to 6 h and 6 to 24 h after dosing. The fractional excretion of sodium, chloride, potassium, calcium, magnesium and inorganic phosphates peaked during the first 2 h and returned almost to the control value during the following two clearance phases. The phase-dependent changes were significant for all electrolytes, except for potassium and inorganic phosphate. Plasma electrolyte levels remained constant throughout the study, except for a small decrease in chloride and potassium and for an increase in calcium and magnesium. Fasting blood glucose and glucose tolerance test were unaffected. A small but significant decrease in LDL-cholesterol was observed on Day 10. Other plasma lipid components showed minor changes. Plasma uric acid levels were moderately increased. There was no significant change of the creatinine clearance. Body weight fell significantly (by about 2 kg) during the study. Tonal audiometry was normal before and after the study. There was no significant difference between the plasma levels of torasemide on Days 1, 10 and 21, nor between its elimination half-life on Days 1 and 21. Side-effects consisted mainly of fatigue and low-back pain on days of intense diuresis.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Diuretic activity, safety and pharmacokinetics of torasemide during chronic treatment in normal subjects. 378 Aug 35

Sensory transduction was studied in dorsal skin mechanoreceptors of the frog, Rana pipiens. The skin was clamped and stretched before being stimulated with the tip of a glass rod mounted on a servo-controlled loudspeaker. Afferent activity was recorded extracellularly from a dorsal cutaneous nerve. Three groups of sensory units could be identified by the size of their recorded action potentials and their response to mechanical stimuli. Action potential amplitudes for the three groups were: less than 50 microV (group I), 50-250 microV (group II) and greater than 300 microV (group III). Group II were selected for further study because of their amplitude and their resistance to fatigue. Three types of mechanical stimuli were used to examine the dynamic properties of group II receptors, steps, sinusoids, and band-limited random displacement. In each case the responses could be well fitted by a power-law model with a fractional exponent of time or frequency. Random stimulation of a large number of group II receptors showed considerable variability in their sensitivity and in their dynamic behavior, as measured by the fractional exponent of frequency. However, the distributions of these two parameters were both unimodal and strongly clustered around the modes, suggesting that the recordings were from a single class of receptors. Varying the temperature of the receptors had little effect on their sensitivity or dynamic properties. This is in contrast to findings on other mechanoreceptors. Doubling the potassium concentration in the bathing solution affected the dynamic properties of the receptors within 5 min but several distinct patterns of change in dynamic behavior were seen.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Sensory transduction in dorsal cutaneous mechanoreceptors of the frog, Rana pipiens. 387 63

A controlled multicentre trial was organised to compare the effects of 20 mg Nifedipine tablets (N) and 2,5 mg Indapamide tablets (I) during a 4 months' treatment period after a placebo period, in 59 patients with moderate essential hypertension (n = 59). The results of blood pressure measurements of 18 patients treated by nifedipine (1 tablet twice daily) and 22 patients treated by indapamide (1 tablet every morning) were compared. The systolic blood pressure, after 10 minutes recumbency, fell from 165 +/- 10 mmHg to 148 +/- 13 mmHg (p less than 0.01), and the diastolic pressure from 104 +/- 6 mmHg to 86 +/- 7 mmHg (p less than 0.01) in the patients treated with nifedipine. In the indapamide group, the SBP fell from 164 +/- 13 mmHg to 152 +/- 15 mmHg (p less than 0.01) and the DBP from 100 +/- 4 mmHg to 87 +/- 6 mmHg (p less than 0.01). There were no significant changes of heart rate with either drug; plasma creatinine, potassium and uric acid concentrations were also unchanged. There was a higher incidence of headaches and tiredness in the nifedipine group, whilst patients treated with indapamide complained more often of muscular cramps. Flushing was observed in nearly a quarter of the patients in both groups. These results confirm that both nifedipine and indapamide induce significant and persistant falls in systolic and diastolic blood pressure. Although the fall was greater with nifedipine than with indapamide, the difference was not statistically significant. The tolerance was satisfactory in both groups of patients.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:[Comparative effects of nifedipine and indapamide in the treatment of arterial hypertension]. 393 9


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