Final answer:
ADH antagonists are used to treat conditions associated with excessive ADH activity, such as hyponatremia and heart failure, by promoting diuresis and reducing water reabsorption. They are also used to decrease blood flow in cases of esophageal bleeding due to vasopressor effects. However, they are contraindicated in diabetes insipidus, where there is an ADH deficiency.
Step-by-step explanation:
The clinical use of an ADH antagonist primarily involves conditions where there is excessive action of antidiuretic hormone (ADH), also known as vasopressin. By blocking the effects of ADH, these antagonists can increase urine output and decrease water reabsorption, which can be beneficial in conditions like hyponatremia or heart failure where there is fluid overload. Another uncommon but important use is to manage life-threatening esophageal bleeding in patients with liver cirrhosis, as ADH can also cause vasoconstriction and reduce blood flow to the bleeding site. In diabetes insipidus, where there's a deficiency of ADH, treatment usually involves administration of synthetic ADH, whereas an ADH antagonist would exacerbate the condition by further increasing urine output.