Skeletal muscle caffeine, effects

Caffeine increases the capacity of skeletal muscle. This effect is probably due to the release of intracellular Ca2+, and is observable in human performance. The contribution of central effects is also likely. Whether caffeine actually benefits exercise is contested (Spriet 1995 Dodd et al. 1993). Research does not consistently support caffeine enhancement of performance during high-intensity, short-term exercise. There is some evidence to suggest benefit during prolonged, moderate-intensity exercise. 

Caffeine is a mild to potent CNS stimulant, with the degree of its stimulating effect dependent on the dose administered. Caffeine stimulates the CNS at all levels, including the cerebral cortex, die medulla, and the spinal cord. Caffeine has mild analeptic (respiratory stimulating) activity. Other actions include cardiac stimulation (which may produce tachycardia), dilatation of coronary and peripheral blood vessels, constriction of cerebral blood vessels, and skeletal muscle stimulation. Caffeine also has mild diuretic activity. 

For over three decades, laboratory research has shown caffeine to be effective at mobilizing calcium in skeletal muscle. In vitro experiments have amply demonstrated that caffeine lowers the excitability threshold and extends the length of muscular contractions via calcium release from the sarcoplasmic reticulum.1012 Caffeine also inhibits calcium reuptake by the sarcoplasmic reticulum, perpetuating calcium availability for muscle work.1318 Also, caffeine promotes increased twitch tension development in muscles.1718... 

Wendt, I. and Stephenson, D., Effects of caffeine on calcium-activated force production in skinned cardiac and skeletal muscle fibers of the rat, European Journal of Physiology, 398, 210, 1983. 

Lopes, J. M., Aubier, M., Jardin, J., Aranda, J. V., and Macklem, P. T., Effects of caffeine on skeletal muscle function before and after fatigue, Journal of Applied Physiology, 54, 1303, 1983. 

The methylxanthines have effects on the central nervous system, kidney, and cardiac and skeletal muscle as well as smooth muscle. Of the three agents, theophylline is most selective in its smooth muscle effects, whereas caffeine has the most marked central nervous system effects. 

Miscellaneous effects. Gastric secretion is increased by caffeine given as coffee (by decaffeinated coffee too) more than by caffeine alone, and the basal metabolic rate may increase slightly (see Skeletal muscle, above). 

The drug produces CNS stimulation and skeletal muscles but to a much lesser extent as compared to caffeine however, it exhibits a greater effect on the coronary dilatation, smooth muscle relaxation, diuresis and cardiac stimulation than caffeine. 

Xanthine derivatives have a number of pharmacological properties in common. Five major actions are observed (1) central nervous system and respiratory stimulation, (2) skeletal muscle stimulation, (3) diuresis, (4) cardiac stimulation, and (5) smooth-muscle relaxation. Caffeine (29) increases central nervous system activity and its main effect is on the cerebral cortex, where it acts to produce clear thought and reduce drowsiness and fatigue. The normal dose is 100-200 mg (Cordell, 1981). The oral LD50 in mouse is 127-137 mg/kg the oral LD50 in rat for theobromine (31) is 950... 

The phosphodiesterase which cleaves cyclic AMP to adenylate is found in both particulate and soluble fractions of tissue homogenates, and it is inhibited by pyrophosphate and ATP, as well as by caffeine, theophylline, and theobromine. These three methylated xanthines cause central nervous system and respiratory stimulation, smooth muscle relaxation, diuresis, coronary dilatation, cardiac stimulation, and skeletal muscle stimulation these effects are believed to be due to increased tissue concentrations of cyclic AMP resulting from inhibition of phosphodiesterase activity. 

Caffeine belongs to a family of naturally occurring compoimds called xanthines. The xanthines, in the form of their plant progenitors, are possibly the oldest known stimulants. They all, to varying extents, stimulate the central nervous system and the skeletal muscles. This stimulation results in an increased alertness, the ability to put off sleep, and an increased capacity for thinking. Caffeine is the most powerful xanthine in this respect. It is the main ingredient of the popular No-Doz keep-alert tablets. Although caffeine has a powerful effect on the central nervous system, not all xanthines are as effective. Thus, theobromine, the xanthine found in cocoa, has fewer central... 

In caffeine-naive subjects, a dose of 4mgkg increases the mean respiratory rate. This effect is not found in chronic caffeine ingestion. Several mechanisms have been suggested, such as an increase in pulmonary blood flow, an increased supply of air to the lungs due to the relaxation of bronchiolar and alveolar smooth muscle, an increase in sensitivity of the medullary respiratory center to carbon dioxide, stimulation of the central respiratory drive, an improved skeletal muscle contraction, and an increase in cardiac output. 

Caffeine has been shown to have a bronchial and smooth muscle relaxant effect and to improve skeletal muscle contractility. Significant increases in hand tremor and forearm extensor electromyogram were observed in human subjects after the ingestion of 6mgkg of caffeine. This effect is more likely due to a CNS stimulatory effect than to direct action on the muscle fibers. Skeletal muscle fatigue can be reversed by high concentrations of caffeine obtained only in vitro but not in vivo. 

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