Describe how nitrates relieve angina.

Nitrates relieve angina primarily by converting to nitric oxide (NO) within the body, which then leads to vasodilation. This process occurs as nitrates are metabolized and released, resulting in the relaxation of smooth muscle in blood vessel walls.

The key mechanism involves the activation of guanylate cyclase, which increases the levels of cyclic guanosine monophosphate (cGMP) in vascular smooth muscle cells. The increased cGMP leads to a series of biochemical events that ultimately result in the relaxation of these muscle cells, causing the dilation of both systemic and coronary blood vessels.

This vasodilation decreases the myocardial oxygen demand by reducing preload (the volume of blood in the ventricles at the end of diastole) and afterload (the resistance the heart must overcome to eject blood). Additionally, the dilation of coronary arteries enhances blood flow to the myocardium, improving oxygen supply during episodes of angina.

While increased oxygen delivery and reduced heart rate may occur as secondary benefits of nitrates' effects on vasodilation, the primary and most direct mechanism by which nitrates relieve angina is through the conversion to nitric oxide and subsequent vasodilation.