In nephrogenic diabetes insipidus, administration of synthetic ADH (DDAVP) typically results in what?

In nephrogenic diabetes insipidus, administration of synthetic ADH (DDAVP) typically results in what?

• A. Urine remains dilute with little or no increase in urine osmolality
• B. Immediate urine concentration and decreased volume
• C. Development of hyponatremia
• D. Marked increase in urine osmolality

Answer: (A)

Nephrogenic diabetes insipidus shows renal insensitivity to vasopressin. Even when a synthetic ADH analog is given, the kidneys cannot respond because the V2 receptor signaling or the aquaporin-2 water channels in the collecting ducts are defective. The result is that water reabsorption in the collecting ducts does not increase, so the urine remains dilute and its osmolality does not rise significantly. This is in contrast to central diabetes insipidus, where DDAVP would markedly concentrate urine and reduce volume. Hyponatremia is not an expected direct outcome here unless there is abnormal water handling beyond the typical insensitivity, and a marked increase in urine osmolality would indicate a responsive system, which nephrogenic DI lacks.

Nephrogenic diabetes insipidus shows renal insensitivity to vasopressin. Even when a synthetic ADH analog is given, the kidneys cannot respond because the V2 receptor signaling or the aquaporin-2 water channels in the collecting ducts are defective. The result is that water reabsorption in the collecting ducts does not increase, so the urine remains dilute and its osmolality does not rise significantly. This is in contrast to central diabetes insipidus, where DDAVP would markedly concentrate urine and reduce volume. Hyponatremia is not an expected direct outcome here unless there is abnormal water handling beyond the typical insensitivity, and a marked increase in urine osmolality would indicate a responsive system, which nephrogenic DI lacks.