**Core Concept**
The question tests the understanding of the body's response to hypovolemic shock, specifically the physiological changes that occur to compensate for a severe haemorrhage. This involves the activation of various **neurohormonal mechanisms** to maintain blood pressure and perfusion of vital organs.

**Why the Correct Answer is Right**
In the event of a severe haemorrhage, the body attempts to compensate for the loss of blood volume by activating the **sympathetic nervous system**, which increases heart rate and vascular tone. This response is mediated by the release of **catecholamines** (such as adrenaline) and other hormones like **vasopressin** (also known as antidiuretic hormone, ADH) to increase blood pressure.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because while some hormones may be released in response to stress, not all are directly involved in the immediate compensation for hypovolemia.
**Option B:** Incorrect as it is not the primary response to acute blood loss.
**Option C:** Incorrect because, although involved in fluid balance, it's not the direct result of the compensatory mechanism for acute haemorrhage.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that in hypovolemic shock, the body's compensatory mechanisms prioritize the perfusion of the brain and heart over other organs, highlighting the importance of promptly addressing the cause of blood loss.

**Correct Answer:** D. Vasopressin (ADH) levels would be elevated above normal levels in response to severe haemorrhage to help retain water and maintain blood pressure.