Which part of the nephron does hydrochlorothiazide (HCTZ) primarily work on?

Hydrochlorothiazide (HCTZ) primarily acts on the early distal convoluted tubule of the nephron. This segment of the nephron is responsible for the reabsorption of sodium and chloride ions, and HCTZ inhibits the sodium-chloride symporter located in this part of the nephron, leading to increased sodium and water excretion. This mechanism is vital in the treatment of hypertension and conditions involving fluid retention, as it contributes to a reduction in blood volume and blood pressure.

The early distal convoluted tubule is specifically involved in the fine-tuning of electrolyte balance after the initial reabsorption that occurs in the proximal convoluted tubule. The action of HCTZ here is distinct from that of other diuretics that may target different segments, such as the proximal convoluted tubule, which primarily reabsorbs a large bulk of filtered sodium and water, or the collecting duct, where other hormones like aldosterone exert their effects. Understanding the specific site of action for HCTZ is essential in pharmacology and physiology, as it helps delineate its therapeutic uses and potential side effects.