Which anti-hypertensive drug works by reducing the water volume in the blood vessels?

Hydrochlorothiazide is a thiazide diuretic that works primarily by promoting the excretion of sodium and water from the kidneys. This action reduces blood volume, which in turn decreases the overall pressure within blood vessels, leading to lowered blood pressure. By inhibiting sodium reabsorption in the distal convoluted tubule of the nephron, hydrochlorothiazide effectively increases urine output, which directly correlates with a reduction in the volume of fluid in circulation. This mechanism is essential for managing hypertension, as it allows the cardiovascular system to operate with less fluid volume, thereby decreasing the workload on the heart and reducing blood pressure.

Other medications listed, such as propranolol, diltiazem, and losartan, have different mechanisms of action. Propranolol is a beta-blocker that reduces heart rate and cardiac output, diltiazem is a calcium channel blocker that relaxes blood vessels, and losartan is an angiotensin II receptor blocker that prevents the effects of a hormone that causes vasoconstriction. None of these directly reduce water volume in the blood in the same way that hydrochlorothiazide does.