What is the first action of the antidiuretic hormone in response to stress?

Antidiuretic hormone (ADH), also known as vasopressin, is released in response to stress, primarily for its role in maintaining fluid balance and blood pressure. When released into the bloodstream, one of ADH's primary actions is to cause the kidneys to retain water. This retention helps to prevent dehydration and maintain blood volume during stressful situations, which is crucial for sustaining blood pressure and overall circulation.

The statement regarding the hormone stopping the flow of water and electrolytes is related to its function of promoting the reabsorption of water within the kidneys. In essence, ADH helps the kidneys conserve water, which consequently leads to a decrease in urine output. This mechanism is vital when the body is under stress, as it helps ensure that essential fluids are preserved.

This function aligns closely with the body's need to conserve resources during times of stress, making the selected answer consistent with the physiological actions of ADH.