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- Eiken, Ola
(author)
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Responses to dynamic leg exercise in man as influenced by changes in muscle perfusion pressure
- 1987
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In: Acta Physiologica Scandinavica Supplementum. - 0302-2994. ; 566, s. 1-37
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Journal article (peer-reviewed)abstract
- The influences of induced alterations in muscle perfusion pressure on the physiological responses to rhythmic exercise in man were investigated. The experiments were carried out in healthy subjects performing leg exercise on a cycle ergometer at light to exhaustive work intensities. Increased muscle perfusion pressure was brought about by exposing the working legs of the supine subject to a subatmospheric pressure of -50 mm Hg (Lower Body Negative Pressure, LBNP), decreased perfusion pressure by instead applying a supraatmospheric pressure of 50 mm Hg (Leg Positive Pressure, LPP). In this way, the perfusion pressure in dynamically exercising large muscle groups could be altered in a controlled fashion. The influences of such manipulation of the perfusion pressure on the physiological adjustments to incremental-load exercise were studied and analysed. The main results and conclusions were as follows: (1) Exercise-induced increases in cardiac output were attenuated by LBNP, an effect caused by curtailment of stroke volume secondary to suction-induced sequestration of blood volume in capacitance vessels not affected by the action of the leg muscle pump. This situation resembles that of dynamic leg exercise in the upright body position. Thus, supine exercise with LBNP at -50 mm Hg seems to be a valid model of upright leg exercise, not only in that it increases perfusion pressure in working muscles but also by causing similar changes in the central circulation as a shift from supine to upright leg exercise. (2) Exercise-induced increases in systolic arterial pressure were markedly exaggerated by LPP, an effect attributable to increased exercise responses in both cardiac output and total peripheral resistance. The exaggerated pressor response supports the notion of a muscle chemoreflex drive in response to flow-restricted exercise tending to reduce the existing flow error. (3) Exercise-induced increases in O2 uptake and blood lactate concentration were both attenuated by LBNP and exaggerated by LPP. The changes in blood lactate levels are attributable to perfusion-pressure dependent variations in muscle blood flow, resulting in opposite changes in the share contributed by anaerobic metabolism to the energy release. Possible explanations for the fact that impaired muscle perfusion was associated with increased O2 uptake at given external work loads are discussed. (4) Exercise-induced responses of the pulmonary ventilation were attenuated by LBNP and markedly exaggerated by LPP.(ABSTRACT TRUNCATED AT 400 WORDS)
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- Jonsdottir, Ingibjörg H, 1966, et al.
(author)
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Physical exercise, endogenous opioids and immune function.
- 1997
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In: Acta physiologica Scandinavica. Supplementum. - 0302-2994. ; 640, s. 47-50
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Research review (peer-reviewed)abstract
- The experimental data available today strongly indicate that various types of physiological stressors, including physical exercise and emotional stress, can influence immune function. Natural immunity represents a first line of defence in viral infections and cytotoxicity to a variety of tumour cells. Natural immunity is strongly influenced by chronic exercise and this regulation includes interaction between the nervous, endocrine and immune systems. Central mechanisms including the endogenous opioids are of great interest. Chronic activation of endogenous opioid systems augments natural cytotoxicity and the possible involvement the opioids in the exercise-induced enhancement of natural immunity is discussed. Also, catecholamines seem to play an important role in the regulation of immune function, both after chronic exercise and emotional stress. The physiological significance of the reported changes in natural cytotoxicity after exercise-training is as yet unclear.
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- Lundgren, Bo, et al.
(author)
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The metabolism of xenobiotics and its relationship to toxicity/genotoxicity : studies with human lymphocytes.
- 1990
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In: Acta Physiologica Scandinavica Supplementum. - 0302-2994. ; 592
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Journal article (peer-reviewed)abstract
- Most compounds considered to be foreign to the human body are rather hydrophobic and chemically inert. Because of their hydrophobicity, xenobiotics enter the body easily by diffusion through biological membranes, are difficult to excrete in unchanged form in the urine and bile and accumulate in hydrophobic compartments of the cell, including the phospholipid bilayer of membranes, where they can disturb normal cellular functions. In order to transform xenobiotics into products which are more readily excretable, enzymes of detoxication first activate these substances (primarily via the cytochrome P-450 monooxygenase system) to intermediates which are often highly electrophilic and reactive, such as epoxides, free radicals and carbonium ions. These intermediates are then partially inactivated and their solubility in water simultaneously increased through the addition of water (by epoxide hydrolases) or conjugation with glutathione (by glutathione transferases). Finally, an additional increase in water solubility can be achieved by conjugation with, for example, sulfate (via sulfotransferases) and/or glucuronic acid (via UDP-glucuronyltransferases). Unfortunately, reactive intermediates of xenobiotic metabolism which are not inactivated sufficiently rapidly can bind covalently to many nucleophilic groups in the cell, including those on DNA, RNA and protein. Most often, because of various cellular defense mechanisms, such binding causes no serious damage. However, in some cases toxic and/or genotoxic effects may be produced. As an alternative to experimentation with animals, we have examined xenobiotic metabolism in circulating mononuclear leukocytes from human beings. Certain enzymes of detoxication--including membrane-bound and cytosolic epoxide hydrolases and cytosolic glutathione transferases--can be easily measured and characterized in preparations from these cells. Autosomal dominant hereditary differences of at least several hundred-fold in the activity of glutathione transferase mu in circulating human lymphocytes were observed, differences which may be of value in predicting an individual's risk for toxic/genotoxic damage after exposure to certain xenobiotics.
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