What does an increase in ADH result in regarding kidney function?

The increase in antidiuretic hormone (ADH), also known as vasopressin, primarily leads to decreased urine output. ADH functions by promoting the reabsorption of water in the kidneys, specifically in the collecting ducts. When ADH levels rise, more water is reabsorbed back into the bloodstream rather than being excreted as urine. This results in more concentrated urine and a reduction in overall urine volume.

In conditions where there is excess ADH, such as in the syndrome of inappropriate antidiuretic hormone secretion (SIADH), individuals can experience significant water retention and a decrease in urine output, which can lead to dilutional hyponatremia. Thus, the correct answer highlights the role of ADH in promoting water reabsorption and subsequently reducing urine output, showcasing its importance in maintaining body fluid balance.