Desmopressin is preferred over vasopressin because desmopressin has all the properties except –
**Core Concept**
Desmopressin and vasopressin are both synthetic analogs of the antidiuretic hormone (ADH) and the vasopressin hormone. Desmopressin is a selective V2 receptor agonist, primarily used to treat central diabetes insipidus and nocturnal enuresis, whereas vasopressin has both V1 and V2 receptor agonist properties, used in various conditions including diabetes insipidus and bleeding esophageal varices.
**Why the Correct Answer is Right**
Desmopressin has a longer duration of action, higher selectivity for the V2 receptor, and a lower pressor effect compared to vasopressin. The V2 receptor agonist activity of desmopressin promotes water reabsorption in the collecting ducts of the kidney, thereby increasing water reabsorption and reducing urine output. Vasopressin, on the other hand, has a shorter duration of action and non-selective agonist activity at both V1 and V2 receptors, which can lead to vasoconstriction and hypertension.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because desmopressin indeed has a longer duration of action compared to vasopressin.
**Option B:** This option is incorrect because desmopressin is highly selective for the V2 receptor, whereas vasopressin has non-selective agonist activity at both V1 and V2 receptors.
**Option C:** This option is incorrect because desmopressin does have a lower pressor effect compared to vasopressin, making it a safer option in certain clinical scenarios.
**Clinical Pearl / High-Yield Fact**
It is essential to note that desmopressin can cause water intoxication, especially in patients with underlying cardiac or renal disease, as excessive water reabsorption can lead to hyponatremia.
**Correct Answer:** D.