What action is promoted by aldosterone?

Aldosterone is a hormone produced by the adrenal glands that plays a crucial role in regulating blood pressure and maintaining electrolyte balance. One of its primary actions is to promote sodium and water retention in the kidneys. This occurs through the increased reabsorption of sodium in the renal tubules, which in turn leads to water retention due to osmotic forces. By increasing the volume of fluid in the bloodstream, aldosterone contributes to an increase in blood pressure.

This mechanism is an important part of the body's response to low blood pressure or low blood volume, as retaining sodium and water helps to restore normal levels and maintain adequate blood circulation. Thus, the correct answer highlights the fundamental effect of aldosterone on fluid balance and its essential role in regulating blood pressure through sodium and water retention.