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

1. The electric properties of the giant synapse in the stellate ganglion of the squid have been further investigated.2. During tetrodotoxin (TTX) paralysis, a local response can be elicited from the terminal parts of the presynaptic axons after intracellular injection of tetraethyl ammonium ions (TEA).3. The response is characterized by an action potential of variable size and duration, whose fall is often preceded by a prolonged plateau. The response, especially the duration of the plateau, is subject to ;fatigue' during repetitive stimulation.4. The TTX-resistant form of activity is localized in the region of the synaptic contacts, and shows a marked electrotonic decrement even within less than 1 mm from the synapse. It is found only on the afferent, not on the efferent, side of the synapse.5. During the plateau of the response, the membrane resistance is greatly reduced below its resting value.6. The response depends on presence of external calcium and increases in size and duration with the calcium concentration. Strontium and barium substitute effectively for calcium. Manganese and, to a lesser extent, magnesium, counteract calcium and reduce the response. The response also declines, and ultimately disappears, if sodium is withdrawn for long periods.7. The relation of the local TTX-resistant response to the influx of calcium ions and to the release of the synaptic transmitter is discussed.
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PMID:Tetrodotoxin-resistant electric activity in presynaptic terminals. 430 10

Intracellular Na+, K+, and Mg2+ concentrations have been measured during the HeLa cell cycle and compared with changes in oxygen utilization and macromolecular synthesis. Cell water content remains relatively constant at 79 +/- 1% during the cell cycle. A biphasic change in intracellular Na+ occurs with low values as cells reach peak S phase and again in early G1. The decrease in S coincides with an increase in cell volume during increased macromolecular synthesis. The fall in intracellular Na+ during mitosis/early G1 coincides with decreased energy utilization as macromolecular synthesis decreases with a continued decrease in [Na+]i in G1 corresponding to a period of increasing cell volume and an increase in protein synthesis. Intracellular Na+ is relatively high during late S/G2 when phosphate incorporation into protein and phospholipid is maximal. Intracellular K+ concentrations largely parallel intracellular Na+ levels although the intracellular K+:Na+ ratio is significantly lower as the cell volume increases during late G2/mitosis. Additions of a Na+-pump inhibitor (strophanthidin) not only caused a rise in [Na+]i and fall in [K+]i but also inhibited protein synthesis. Conversely, addition of a protein synthesis inhibitor (cycloheximide) blocked amino acid incorporation and produces a fall in intracellular Na+ levels. These findings indicate that intracellular Na+ and K+ play an important role in regulating cell hydration during the cell cycle and that changes in Na+, K+-ATPase activity, synthesis and/or utilization of high energy phosphate compounds, fluid phase turnover (endocytosis), Na+:H+ exchange (pHi), Donnan forces, and ionic adsorption may all be involved.
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PMID:Changes in intracellular cations during the cell cycle in HeLa cells. 609 99

There is a close epidemiological association between obesity and elevated blood pressure for all age groups, although not every obese individual becomes hypertensive. In populations without age-related increases in body weight, an elevation of blood pressure with age is not seen. Mechanisms included in the development of hypertension in obesity are hyperinsulinemia, insulin induced sodium retention and increased sympathetic tone. Overnutrition with over intake of sodium and lack of physical exercise contribute to the metabolic syndrome of obesity. Thus, weight reduction by decreased energy uptake and increased physical exercise is recommended in the treatment of hypertension in obese patients. The resulting fall in insulin levels may lead to decreased sodium absorption in the kidney. Although treatment of obesity by weight loss decreases blood pressure substantially, a minority of patients do not respond to the weight loss. Blood pressure generally decreases before normal weight is achieved. Salt intake reduction does not appear to explain why weight reduction lowers blood pressure. Reduced levels of plasma renin activity, serum aldosterone levels, catecholamine levels and serum insulin levels may be involved in the blood pressure lowering associated with weight loss. Since the risk of cardiovascular disease in the hypertensive patient is not only determined by the blood pressure, an overall treatment which aims at reduction of other risk factors such as glucose intolerance and hyperlipoproteinemia is advocated. Thus, in any obese hypertensive patient normalization of excess body weight and increased physical activity appears to be the first and most important step of any rational therapeutic strategy.
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PMID:Obesity and hypertension: epidemiology, mechanisms, treatment. 636 45

The effect of the converting enzyme inhibitor captopril as long term treatment was investigated in 14 patients with severe congestive heart failure in a double blind trial. Captopril reduced plasma concentrations of angiotensin II and noradrenaline, with a converse increase in active renin concentration. Effective renal plasma flow increased and renal vascular resistance fell; glomerular filtration rate did not change. Serum urea and creatinine concentrations rose. Both serum and total body potassium contents increased; there were no long term changes in serum concentration or total body content of sodium. Exercise tolerance was appreciably improved, and dyspnoea and fatigue lessened. Left ventricular end systolic and end diastolic dimensions were reduced. There was an appreciable reduction in complex ventricular ectopic rhythms. Adverse effects were few: weight gain and fluid retention were evident in five patients when captopril was introduced and two patients initially experienced mild postural dizziness; rashes in two patients did not recur when the drug was reintroduced at a lower dose; there was a significant reduction in white cell count overall, but the lowest individual white cell count was 4000 X 10(6)/l. Captopril thus seemed to be of considerable value in the long term treatment of severe cardiac failure.
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PMID:Captopril in heart failure. A double blind controlled trial. 638 12

The purpose of this study was to investigate the contractile response of skeletal muscle in situ when stimulation results in an unfused tetanic contraction. The left gastrocnemius-plantaris muscle group of anesthetized (pentobarbital sodium) dogs (n = 16) was connected to an isometric lever and stimulated indirectly for 30 min. During 10-Hz stimulation, total tension (the peak of each oscillation in tension) increased during the first 2 min of stimulation (staircase), then decreased during the remaining 28 min of stimulation. Since relaxation was incomplete at this rate of stimulation, the developed tension, the difference between peak tension and the lowest tension between successive contractions, did not follow the same pattern of staircase and fatigue as the peak tension did. Developed tension (delta T) decreased during the staircase response then increased from 2 to 10 min before finally decreasing again during the last 20 min, ending at 56 +/- 15 (mean +/- SE) % of the initial (first contraction) delta T. At 2 min of 10-Hz contractions, half-relaxation time (1/2 RT) was too long to measure (insufficient relaxation between contractions), but later, 1/2 RT decreased from greater than 65 ms to less than 40 ms. Increased 1/2 RT has been associated with reduced energy availability. If an increased 1/2 RT is an indication of insufficient energy, then it can be concluded that fatigue continued in spite of a recovery of energy supplies. This suggests a possible dissociation of fatigue and energy availability.
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PMID:Fatigue from incompletely fused tetanic contractions in skeletal muscle in situ. 641 14

12 Brazilian men were treated with gossypol for 1 year. The treatment schedule consisted of oral administration of 20 mg gossypol daily for 4 months, followed by a maintenance dose of 20 mg on alternate days (o days/week), totaling 60 mg weekly for 8 months. 10 men became azoospermic at the end of the 4th month of treatment, and the other 2 developed marked oligospermia with necrospermia. Except for 1 man who complained of transient listlessness and fatigue, the subjects reported no side effects during treatment. No changes in libido or potency were reported, and plasma testosterone remained unchanged. Blood chemistry values, which included complete blood cell count, cholesterol, glucose, triglycerides, acid phosphatase, urea, transaminases, sodium, and potassium, were not changed significantly during treatment. The response of the pituitary to gonadotropin-releasing hormone stimulation and the response of the testis to gonadotropin stimulation appeared normal in men treated with gossypol. After treatment, sperm counts reverted to essentially normal levels in 8 of 12 men. In 4 men, azoospermia continued 1 year after gossypol treatment discontinuation. Retrograde phlebography carried out in 3 of 4 men who remained azoospermic after therapy discontinuation revealed subclinical varicocele.
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PMID:Antispermatogenic action of gossypol in men. 646 76

Mg2+-selective microelectrodes have been used to measure the intracellular free Mg2+ concentration in frog skeletal muscle fibers. Glass capillaries with a tip diameter of less than 0.4 micron were backfilled with the Mg2+ sensor, ETH 1117. In the absence of interfering ions, they gave Nernstian responses between 1 and 10 mM free Mg2+. In the presence of an ionic environment resembling the myoplasm, the microelectrode response was sub Nernstian (18-24 mV) but still useful. The electrodes were calibrated before and after muscle-fiber impalements . In quiescent fibers from sartorius muscle (Rana pipiens), with resting membrane potentials not less than -82 mV, the intracellular free Mg2+ concentration was 3.8 +/- 0.41 (S.E.) mM (n = 58) at 22 degrees C. No significant change in the intracellular free Mg2+ was observed following extensive (approx. 6 h) incubation in Mg2+-free media. Increasing the external concentration of magnesium from 4 to 20 mM (approx. 15 min) produced a slow and small enhancement (1.8 mM) of [Mg2+]i, which was fully reverted when the divalent cation was removed from the bathing solution. No change in ionic magnesium resting concentration was observed when the muscle fibers were treated either with caffeine 3 mM or with Na+-free solutions. In depolarized muscle fibers (-23 +/- 2.7 mV) treated with 100 mM K+, the myoplasmic [Mg2+] was 3.7 +/- 0.45 (S.E.) mM, n = 6, immediately after the spontaneous relaxation of the contracture. Similar determinations in muscle fibers during stimulation at low frequency (5 Hz), and after fatigue development, showed no changes in the concentration of free cytosolic Mg2+. These results point out that [Mg2+]i is not modified under these three different experimental conditions.
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PMID:Direct measurement of intracellular free magnesium in frog skeletal muscle using magnesium-selective microelectrodes. 660 20

In North America, diuretics remain the most common first-line drug therapy for essential hypertension based on efficacy, safety and cost. The promotion of step-care programmes has firmly established their dominant use on this continent whereas in Europe, particularly in Scandinavia and Great Britain, beta-adrenoceptor blocking agents are more frequently chosen as first-line therapy. On both continents, combined therapy with a diuretic and a beta-blocker is probably the most common second step for patients with blood pressures uncontrolled on a single agent alone and diuretics remain useful, if not essential, to prevent sodium retention commonly observed with other antihypertensive agents. Although the forced loss of sodium and water may be responsible for their initial antihypertensive effect, the mechanism underlying their long-term effect is unknown but probably involves some alteration of vascular smooth muscle reactivity. More recently, concern has been expressed about their long-term safety as larger populations are being exposed to diuretic agents for a significant proportion of their life-span. These concerns include haemodynamic and biochemical consequences of diuretic therapy - excessive tachycardia at rest and with minimal exercise, postural hypotension, hypokalaemia and arrhythmias, muscle cramps or fatigue, glucose intolerance, hyperuricaemia and altered circulating lipids as markers or promotors of atherosclerosis and its complications. At present, there is insufficient evidence to alter the present recommendation of diuretic agents as first-line drug therapy in the treatment of hypertension.
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PMID:Diuretic treatment in essential hypertension. 661 41

Septic shock was induced in adult baboons by the infusion of live Escherichia coli. A progressive derangement in skeletal muscle cell function was documented by the direct measurement of declining transmembrane potential difference (PD). A concurrent depolarization of the red blood cell (RBC) was characterized by cellular uptake of chloride, sodium, and water, and loss of potassium. The decrease in RBC PD was significantly greater than the change predicted to occur from acidosis alone. These findings are compatible with changes in membrane permeability and decreased active transport. The continuous accumulation of RBC adenosine triphosphate during shock suggests decreased energy utilization rather than decreased energy production as a factor leading to diminished active ion transport.
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PMID:Changes in red blood cell transmembrane potential, electrolytes, and energy content in septic shock. 662 Apr 30

The premenstrual symptom complex many women experience in a moderate to severe form can be divided into four subgroups. Because there is more than one syndrome and nervous tension is one of the most common symptoms, the term premenstrual tension syndromes (PMTS) is used. The most common subgroup, PMT-A, consists of premenstrual anxiety, irritability and nervous tension, sometimes expressed in behavior patterns detrimental to self, family and society. Elevated blood estrogen and low progesterone have been observed in this subgroup. Administration of vitamin B6 at doses of 200-800 mg/day reduces blood estrogen, increases progesterone and results in improved symptoms under double-blind conditions. Women in this subgroup consume an excessive amount of dairy products and refined sugar, and progesterone may be of value in them. The second-most-common subgroup, PMT-H, is associated with symptoms of water and salt retention, abdominal bloating, mastalgia and weight gain. The severe form of PMT-H is associated with elevated serum aldosterone. Vitamin B6 at high dosage suppresses aldosterone and results in diuresis and clinical improvement. Vitamin E helps the breast symptoms. Methylxanthines and nicotine should be curtailed and sodium limited to 3 gm/day. PMT-C is characterized by premenstrual craving for sweets, increased appetite and indulgence in eating refined sugar followed by palpitation, fatigue, fainting spells, headache and sometimes the shakes. PMT-C patients have increased carbohydrate tolerance and low red-cell magnesium. Adequate magnesium replacement results in improved glucose tolerance tests and decreased PMT-C symptoms. Deficiency of the prostaglandin PGE1 may also be involved in PMT-C. PMT-D is the least common but most dangerous because suicide is most frequent in this subgroup. The symptoms are depression, withdrawal, insomnia, forgetfulness and confusion. In ten PMT-D patients the mean blood estrogen was lower and the mean blood progesterone higher than normal during the midluteal phase. Elevated adrenal androgens are observed in some hirsute PMT-D patients. Two PMT-D patients with normal blood progesterone and estrogens had high lead levels in hair tissue and chronic lead intoxication. This subgroups needs careful medical attention when the symptoms are severe. Therapy should be individualized according to the results of the evaluation.
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PMID:Nutritional factors in the etiology of the premenstrual tension syndromes. 668 67


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