What is diabetes insipidus primarily caused by?

Diabetes insipidus is primarily caused by a deficiency of the antidiuretic hormone (ADH), also known as vasopressin, or by the body's resistance to this hormone. ADH plays a critical role in maintaining the body’s fluid balance by regulating the amount of water reabsorbed by the kidneys. When there is insufficient ADH secretion, the kidneys fail to reabsorb water effectively, leading to excessive urination and increased thirst. This is a key feature of diabetes insipidus, differentiating it from diabetes mellitus, which involves issues with insulin and blood glucose levels.

While insulin deficiency and increased serum glucose levels are relevant to diabetes mellitus, they do not pertain to diabetes insipidus. Similarly, excessive production of catecholamines affects other physiological processes and is not related to the mechanisms underlying diabetes insipidus. Thus, the correct answer reflects the direct relationship between ADH and the pathophysiology of diabetes insipidus.