Aminophylline inhibits which enzyme –
**Core Concept**
Aminophylline is a phosphodiesterase inhibitor, which means it works by inhibiting the enzyme phosphodiesterase (PDE). This enzyme is responsible for breaking down cyclic adenosine monophosphate (cAMP), a crucial second messenger in cellular signaling pathways.
**Why the Correct Answer is Right**
Aminophylline, being a phosphodiesterase inhibitor, increases the levels of cAMP in the cell. This leads to relaxation of smooth muscle, particularly in the airways, making it useful in treating asthma and chronic obstructive pulmonary disease (COPD). The increased cAMP also enhances the release of histamine, which can worsen bronchospasm, but the net effect is bronchodilation.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because aminophylline does not inhibit the enzyme acetylcholinesterase, which is responsible for breaking down acetylcholine, a neurotransmitter involved in muscle contraction.
**Option B:** This option is incorrect because aminophylline does not inhibit the enzyme angiotensin-converting enzyme (ACE), which is involved in the renin-angiotensin-aldosterone system and blood pressure regulation.
**Option C:** This option is incorrect because aminophylline does not inhibit the enzyme beta-glucosidase, which is involved in carbohydrate metabolism.
**Clinical Pearl / High-Yield Fact**
Aminophylline can have a narrow therapeutic index, and its use should be monitored closely due to the risk of toxicity, particularly in patients with heart disease.
**Correct Answer:** D. Phosphodiesterase (PDE)