A 75-year-old man has angina pectoris for years.

While watching television, he became excessively agitated and began to

experience a paroxysmal pressing or crushing chest pain, often radiating into

his neck and left upper extremity. As he is already familiar with this

symptoms, he knows that this is an angina attack. It is caused by transient

myocardial ischaemia (lack of blood flow) associated with physical activity,

emotional stress or cold. He will therefore take nitroglycerin, a drug designed

to manage this acute attack. The pain actually goes away in 5 minutes after

taking it. The drug is converted into nitrosothiol by the action of free SH

groups of glutathione, from which nitric oxide is released in the endothelium.

What effect does the NO produced have on the vessel?