A patient presents with severe dehydration and is excreting large volumes of dilute urine. Clinical investigations reveal that the juxtaglomerular (JG) cells and the adrenal cortex are functioning normally, with adequate levels of circulating aldosterone. Which of the following specific defects is most likely responsible for this condition?

Step-by-step solution

The excretion of large amounts of dilute urine (diuresis) despite severe dehydration indicates a failure in the facultative reabsorption of water in the latter parts of the renal tubules (distal convoluted tubule and collecting duct). Since the adrenal cortex and aldosterone levels are normal, the defect lies in the antidiuretic hormone (ADH) pathway. ADH, or vasopressin, is secreted by the neurohypophysis (posterior pituitary) and facilitates water reabsorption. Its hyposecretion leads to water loss and dilute uri