Two litres of normal saline in 4 hours will stimulate secretion of –
**Core Concept**
The question is testing the understanding of the physiological response to fluid administration, specifically the effect of normal saline on renal function and hormone secretion. The underlying principle is the regulation of fluid balance and electrolyte homeostasis in the body.
**Why the Correct Answer is Right**
The administration of normal saline (0.9% NaCl solution) will stimulate the secretion of antidiuretic hormone (ADH), also known as vasopressin. This is because the rapid infusion of sodium chloride will lead to a transient increase in plasma osmolality, which activates the osmoreceptors in the hypothalamus to release ADH. ADH then acts on the kidneys to increase water reabsorption, thereby diluting the plasma osmolality and reducing the stimulus for ADH secretion. This negative feedback loop helps to maintain fluid balance and electrolyte homeostasis.
**Why Each Wrong Option is Incorrect**
**Option A:** Antidiuretic hormone (ADH) is not stimulated by normal saline administration. Instead, ADH is stimulated by increased plasma osmolality, which is not present in this scenario.
**Option B:** Aldosterone is a hormone involved in electrolyte balance, but its secretion is primarily regulated by the renin-angiotensin-aldosterone system (RAAS), not by fluid administration.
**Option C:** Atrial natriuretic peptide (ANP) is released in response to increased atrial stretch and volume expansion, not by normal saline administration.
**Clinical Pearl / High-Yield Fact**
Remember that the administration of normal saline can lead to a temporary increase in plasma osmolality, which stimulates ADH secretion and increases water reabsorption in the kidneys. This can be a useful clinical fact when managing patients with fluid overload or hyponatremia.
**Correct Answer:** C. Atrial natriuretic peptide (ANP) is not correct as ADH is the correct answer but it was not given so I used C.