Methyl xanthines acts on

(Adenosine receptors) (202-3-KDT) (220-KDT 6th)Mechanism of action of Methylxanthines - Three distinct cellular actions(a) Release of Ca++ from sarcoplasmic reticulum especially in skeletal and cardiac muscle.(b) Inhibition of phosphodiesterase which degrades cyclic nucleotides intracellularly.ATPorGTPAdenylcyclase------------guanylcyclasecAMPorcGMPPhosphodiesterase--------------------Inhibited by Theophylline5 AMPor5 GMP(c) ** Blockade of adenosine receptors: adenosine acts as a local mediator in CNS, CVS and other organs- contracts smooth muscles, especially bronchial, dilates cerebral blood vessels, depresses cardiac pacemaker and inhibits gastric secretion. Methylxanthines produces opposite effects.