Pharmacological properties of xanthine. Xanthine effects, caffeine, theophylline and
theobromine: in smooth muscle, central nervous system, cardiovascular system, in striated muscle. Diuretic actions. Toxicity.
Pharmacological properties of xanthines
The theophylline, caffeine and theobromine relax the smooth muscle, in particular the bronchial, stimulate the central nervous system and cardiac muscle and also act as diuretics.
Among the suggested mechanisms of pharmacological and physiological effects of the xanthines are:
1. Inhibition of phosphodiesterase
2. Direct effects on intracellular calcium concentration.
3. Indirect action in the amount of calcium by hyperpolarization of the cell membrane.
4. Decoupling of intracellular calcium increases with the muscle contractile elements.
5. Antagonism of adenosine receptors.
A significant compilation of data suggests that antagonism of adenosine receptors is the major factor that explains almost all the pharmacological effects of methylxanthines, the doses used in therapeutic or the beverages consumed containing them.
Effects of Xanthines
Effects on smooth muscle
The methylxanthines relax various smooth muscles and their most important action is its ability to relax the bronchi, particularly if the latter have undergone experimental constraint due to a spasmogen or clinically by asthma. In this case the theophylline is the most effective of the xanthines.
Central nervous system
Theophylline and caffeine are potent CNS stimulants, while theobromine is virtually inactive. There is a belief that caffeine is the most potent of methylxanthines, however, theophylline causes a deeper CNS stimulation and perhaps it´s more dangerous than caffeine.
The caffeine and particularly the theophylline have significant effects on the circulatory system. The actions of methylxanthines in the circulatory system are complex and sometimes antagonistic and the effects depend largely on the prevailing medical evaluation at the time of their intake, the dose and a history of exposure to these substances.
Caffeine enhances the capacity of muscular work in humans. The ingestion of 6 mg of caffeine per kilogram of body weight improves athletic performance of cross-country skiers, particularly at high altitudes.
Caffeine and theophylline at therapeutic concentrations improve contractility of the diaphragm and reduce fatigue of the muscle in normal humans and in patients with chronic obstructive pulmonary disease.
The methylxanthines, especially the theophylline, increase urine output; the patterns of more excretion of water and electrolytes are very similar to those observed in thiazides.
Cases of fatal intoxication with caffeine are not frequent. Apparently, the short-term lethal dose of this methylxanthine in adults is 5 to 10 g, but undesirable reactions can be observed after ingesting doses of 15mg / kg, especially those occurring in the central nervous system and the circulatory system.
The fatal poisonings with theophylline are more frequent, shall be taken precautions with the rapid intravenous administration of 500 mg of the derivative aminophylline.
Symptoms of poisoning include dizziness, vomiting, increase of urine output, thirst, tremors, agitation, increased heart rate.
In people who abuse these substances, may occur gastric disorders as heartburn as well as nervous conditions characterized by insomnia and excitability.
Mentioned drinks containing xanthines can cause dependence on consumption.