Mechanism of action of NO -

Ans. is 'b' i.e., |cGMP o Nitric oxide (NO) released from parasympathetic nonadrenergic noncholinergic (NANS) nerves and vascular endothelium is the major neurotransmitter causing relaxation of smooth muscles of arteries, arterioles and trabeculae of sinusoids, i.e., NO is the major transmitter responsible for penile erection.o NO causes smooth muscle relaxation by generating cGMP.o cGMP is degraded by the enzyme phosphodiesterase, especially isoenzyme phosphodiesterase type 5 (PDE-5) which is selectively active in penile smooth muscles.