Thiazides primarily reduce blood pressure through what action?

Thiazides primarily reduce blood pressure through the mechanism of vasodilation. These diuretics work by inhibiting sodium reabsorption in the distal convoluted tubule of the nephron, leading to increased excretion of sodium and water, which decreases blood volume and subsequently lowers blood pressure. While the primary action of thiazides is diuretic, their long-term effects also include vasodilation due to a decrease in sodium levels in the vascular smooth muscle. This results in relaxation of blood vessels, contributing to a reduction in peripheral vascular resistance and thus lowering blood pressure.

Other options involve mechanisms that do not effectively explain how thiazides work. Increasing heart rate is contrary to the desired effect of blood pressure control, as a higher heart rate could raise blood pressure. Increasing calcium absorption is not a primary action of thiazides; instead, they can lead to increased calcium reabsorption in the kidneys, which is a different mechanism not directly related to blood pressure reduction. Increasing peripheral vascular resistance would typically elevate blood pressure rather than reduce it. Therefore, the action of vasodilation is most accurately aligned with how thiazides play a role in managing hypertension.