Sildenafil acts by inhibiting -

Ans. is 'b' i.e., Phosphodiesterase - 5o Sildenafil is used to treat Erectile DysfunctionMechanism of action:o Penile tumescence during sexual arousal is improved, but it has no effect on penile tumescence in the absence of sexual activity', because sexual stimulation results in smooth muscle relaxation of the corpus cavemosum, increasing the inflow of blood.o Sildenafil in addition, weakly inhibits the isoenzyme PDE-6 which is involved in photoreceptor transduction of retina - impairment in colour vision especially blue green discrimnation.