This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: A.N.S., Subject name: Pharmacology
Mechanism of action of aminophylline in bronchial asthma: 
Select and explain. 
A. Decreasing phosphodiesterase activity, B. Direct action on smooth muscles, C. Releasing catecholamines, D. Stabilizing membrane of mast cells
A: Decreasing phosphodiesterase activity
Answer: A: Decreasing phosphodiesterase activity 
Explanation: Aminophylline and other methylxanthines act byInhibiting phosphodiesterase enzyme causing - cAMPBlocking adenosine receptorsReleasing Ca2+ from sarcoplasmic reticulum in cardiac and skeletal muscles.Use-Asthma, COPD, chronic bronchitis