A 21-year-old woman with primary pulmonary hypertension is treated with bosentan. What receptors are most likely being blocked as a result of this treatment?

• A. Angiotensin II receptors
• B. Calcium channels
• C. Endothelin receptors
• D. Voltage-gated sodium channels

Answer: (C)

Bosentan is a medication specifically designed to treat pulmonary arterial hypertension by acting as an antagonist. In this case, bosentan predominantly blocks endothelin receptors, which are located on vascular smooth muscle and endothelial cells. Endothelin-1 is a potent vasoconstrictor that contributes to elevated blood pressure in pulmonary arteries.

By inhibiting the action of endothelin-1 through these receptors, bosentan helps to relax and dilate the blood vessels, leading to a decrease in pulmonary arterial pressure. This therapeutic mechanism is crucial for improving blood flow and reducing the symptoms associated with primary pulmonary hypertension.

The other receptor types mentioned in the choices do not relate to bosentan's mechanism of action: angiotensin II receptors are targeted by different antihypertensive agents; calcium channels are addressed by calcium channel blockers; and voltage-gated sodium channels are implicated in antiarrhythmic therapies. Thus, the most accurate choice, reflecting the specific action of bosentan, is blocking endothelin receptors.