Caffeine diuretic action

These compounds competitively inhibit phosphodiesterase, resulting in an increase in cyclic AMP (see Box 14.3) and subsequent release of adrenaline. This leads to the major effects a stimulation of the central nervous system (CNS), a relaxation of bronchial smooth muscle, and induction of diuresis. These effects vary in the three compounds. Caffeine is the best CNS stimulant, and has weak diuretic action. Theobromine has little stimulant action, but has more diuretic activity and also muscle relaxant properties. Theophylline also has low stimulant action and is an effective diuretic, but it relaxes smooth muscle better than caffeine or theobromine. 

A much milder and legal stimulant is caffeine, depicted in Figure 14.27. A number of mechanisms have been proposed for caffeines stimulatory effects. Perhaps the most straightforward mechanism is caffeine s facilitating of the release of norepinephrine into synaptic clefts. Caffeine also exerts many other effects on the body, such as dilation of arteries, relaxation of bronchial and gastrointestinal muscles, diuretic action on the kidneys, and stimulation of stomach-acid secretion. 

The general properties of the methylxanthines (theophylline, caffeine) are discussed elsewhere (see p. 194). Their mild diuretic action probably depends in part on smooth muscle relaxation in the afferent arteriolar bed increasing renal blood flow, and in part on a direct inhibitory effect on salt reabsorption in the proximal tubule. Their uses in medicine depend on other properties. 

Caffeine s primary action is stimulation of CNS activity but, as we saw, caffeine is distributed freely throughout the body. Such distribution is evidenced by caffeine s actions outside the CNS contraction of striated muscle, including the heart relaxation of smooth muscle, especially the coronary arteries, uterus, and bronchi diuretic effects on the kidneys at higher doses, a stimulating effect on respiration elevation of basal metabolism and various endocrine and enzymatic effects (Levenson Bick, 1977 Rail, 1990a). Caffeine s effects on the body s systems provide good evidence for the blockade of adenosine receptors as its mechanism of action because caffeine s effects essentially arc opposite to those of adenosine (Leonard et al., 1987). 

Theophylline occurs in such a low concentration in all xanthine drugs that extraction is not profitable. Theophylline can be produced by demethylation of caffeine or by total synthesis. Theophylline has a spasmolytic effect on smooth muscles, which is apparent in a pronounced bronchodilating action, hence it is used in asthma either on its own or combined with ethylenediamine to produce aminophylline. Furthermore, theophylline has a diuretic action. 

Caffeine is a potent central stimulant. It also acts on the cardiac muscle and on the kidneys. It stimulates the higher centres of the CNS thereby causing enhanced mental alertness and wakefulness. Caffeine helps in the stimulation of respiratory centres. Its diuretic action is due to enhanced glomerular filtration rate, increased renal blood flow and above all the reduction of the normal tubular reabsorption. 

Tolerance to the diuretic action of caffeine was demonstrated more than 50 years ago and was shown to develop on chronic caffeine intake so that the clinical significance of hypokalemia and calciuria is difficult to evaluate. Although controversial, some epidemiological studies have implicated caffeine in the increased risk for poor calcium retention. For calcium intakes lower than 750 mg per day, increased rate of bone loss and lower bone density were reported. However, it has been suggested that the effect on bone of high caffeine intake requires a genetic predisposition toward osteoporosis. In individuals who ingest calcium recommended daily allowances, there is no evidence of any effect of caffeine on bone status and calcium economy. 

C7H9N402- M.p. 337 C, an alkaloid obtained from cacao seeds or prepared synthetically. Constitutionally it is similar to caffeine, and is also a weak base. It is usually administered as the sodium compound combined with either sodium ethanoate or sodium salicylate, and is employed almost entirely as a diuretic. Physiologically theobromine resembles caffeine, but its effect on the central nervous system is less, while its action on the kidneys, is more pronounced. 

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. 

Caffeine and the related dimethylxanthines have similar pharmacological or therapeutic effects and similar toxic effects. The primary actions include stimulation of the central nervous system, relaxation of bronchial muscles, mild cardiac muscle stimulation, and diuretic effects on the kidney. 

Diuretics have many different mechanisms of action, but all of them affect transport activity or water reabsorption along the nephron and collecting duct system. Over-the-counter orally administered diuretics can contain chemically active ingredients such as pamabrom or caffeine (3,7-dihydro-l,3,7-trimethyl-lH-purine-2,6-dione C8H4QN4O2). In 1955,... 

These all resemble each other in most points of their pharmacological action, but they differ markedly in the relative intensity of their action on various functions. Thus, caffeine is the most potent central nervous system (CNS) stimulant of the group theobromine exerts the greatest action on the muscles and theophylline is the most effective diuretic and coronary dilator. Theobromine has comparatively little effect on the CNS, whereas theophylline has no action on the muscles. 

The diuretic effects of caffeine are less than those of theobromine and theophylline. Caffeine may enhance renal blood flow and glomerular filtration rate, but its main action may be attributed to the reduction of the normal tubular reabsorption. 

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