ABSTRACT
This chapter provides a brief overview of the basic metabolism and physiological effects of caffeine and other methylxanthines. Caffeine and other methylxanthines are essentially non-ionized under physiological conditions. Free fatty acids and glycerol rise in the plasma following caffeine and methylxanthine administration, showing a major effect on adipose tissues. The primary use of caffeine is that of a central nervous system stimulation. The body responds to chronic presence of caffeine by increasing the number of adenosine receptor sites. This may be one of the reasons for the increased tolerance to caffeine in heavy coffee and tea drinkers. The often severe headaches, common in caffeine withdrawal, appear to be caused by vasodilation of cerebral blood vessels. This action is probably mediated by the action of the methylxanthines on adenosine receptors. Electrophysiological changes take place in the human heart even under the influence of limited doses of caffeine.
