This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Prostate and seminal vesicles, Subject name: Surgery
Mechanism of action of Silodosin: 
Select and explain. 
A. Alpha antagonist, B. Beta antagonist, C. Anticholinergic, D. PDE5 inhibitor
A: Alpha antagonist
Answer: A: Alpha antagonist 
Explanation: MEDICAL THERAPY IN BPH * Alpha-blockers: (Prazosin, terazosin, doxazosin, tamsulosin, alfuzosin, silodosin) Relaxes smooth muscle & decreases urethral resistance. Side effects: ohostatic hypotension, dizziness, tiredness, retrograde ejaculation, rhinitis & headache. * 5-Alpha-reductase Inhibitors: (Finasteride, dutasteride, triptorelin pamoate)