Which of the following would trigger an increase in ADH release?

Antidiuretic hormone (ADH), also known as vasopressin, plays a crucial role in regulating body fluid balance and maintaining homeostasis. It is primarily released by the posterior pituitary gland in response to various physiological stimuli.

High blood sodium levels serve as a significant trigger for the release of ADH. When sodium levels in the blood increase, it often indicates that the body is becoming dehydrated or that there is excess solute in relation to the amount of water. To counteract this effect, the body releases more ADH. ADH promotes water reabsorption in the kidneys, helping to dilute the sodium concentration in the blood and conserve water in the body. This mechanism helps to maintain osmotic balance and proper hydration levels, making it an essential response to elevated sodium levels.

In contrast, increased fluid intake or normal blood volume would generally lead to a decrease in ADH release. Similarly, decreased metabolic activity does not directly impact ADH levels in the way that high sodium levels do, as metabolic activity does not provide information about the hydration status of the body. Therefore, among the options provided, high blood sodium levels are the primary driver for increased ADH release.