This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Asthma, Subject name: Pharmacology
[{'content': 'Methyl xanthines acts on \nSelect and explain. \nA. Histamine receptors, B. Adenosine receptors, C. Mast cells, D. Cholinergic receptors', 'role': 'user'}, {'content': 'Answer: B \nExplanation: (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.', 'role': 'assistant'}]