What is the primary mechanism of action of Hydrochlorothiazide?

Hydrochlorothiazide primarily acts as a diuretic by interfering with the reabsorption of sodium and chloride in the distal convoluted tubule of the nephron. This action leads to increased excretion of sodium and chloride in the urine, resulting in osmotic effects that draw water along with these ions, thereby increasing urine output. The reduction in sodium reabsorption effectively helps lower blood volume and blood pressure, making it a useful treatment for hypertension and edema.

The other choices reflect mechanisms that do not accurately describe hydrochlorothiazide's primary action. For example, while potassium retention may be a consequence of some diuretics, hydrochlorothiazide can actually lead to loss of potassium, not retention. Moreover, it does not primarily work by increasing water reabsorption; in fact, it promotes more water excretion through its effect on sodium and chloride. Lastly, hydrochlorothiazide does not block the renin-angiotensin system; that action is characteristic of other classes of medications such as ACE inhibitors and ARBs (Angiotensin Receptor Blockers). Thus, the accurate characterization of hydrochlorothiazide’s mechanism of action is critical for understanding how this drug contributes to managing conditions like hypertension.