As a knowledgeable nurse, you know that the action of nitrates is:
A. Smooth muscle contraction
B. Vasoconstriction
C. Smooth muscle relaxation
D. Increase preload
Correct Answer: C. Smooth muscle relaxation
Nitrates cause smooth muscle relaxation, vasodilation, reduction of preload, and improved blood flow to the myocardium. Nitrates exert their pharmacological effect by being activated by mitochondrial or cytosolic aldehyde dehydrogenase (ALDH2) into nitric oxide (NO), an endothelium-derived relaxing factor (EDRF). NO is generally produced by the endothelium to dilate the blood vessels; however, endothelial dysfunction in diseases such as atherosclerosis can deplete NO levels. Other choices have the opposite effect of nitrates.
Option A: The decreased intracellular calcium levels subsequently inhibit myosin light chain kinase, and the unphosphorylated myosin light chain causes myosin head to detach from actin, resulting in smooth muscle relaxation.
Option B: Nitrates exert their effects by dilating venous vessels, coronary arteries, and small arterioles; its maximal vasodilation is in the venous vessels.
Option D: The venodilation increases the venous capacitance and lowers the preload; this subsequently lowers the left ventricular end-diastolic pressure, resulting in a reduction in myocardium workload, which decreases the oxygen demand of the heart.