American Board of Surgery Qualifying Exam (ABS QE) Practice Test

What is the primary action of vasopressin at V1 receptors?

1. Increased water reabsorption

2. Arterial constriction

3. Vasodilation

4. Increase in heart rate

The correct answer is: Arterial constriction

Vasopressin, also known as antidiuretic hormone (ADH), binds to V1 receptors primarily located on vascular smooth muscle. The activation of these receptors leads to arterial constriction, which plays a crucial role in regulating blood pressure. When vasopressin binds to the V1 receptors, it triggers a series of intracellular signaling pathways that result in the contraction of smooth muscle fibers in blood vessels, ultimately causing vasoconstriction. This response is critical during situations like hemorrhage or low blood volume, where the body needs to maintain or increase blood pressure to ensure adequate blood flow to vital organs. The other options describe mechanisms associated with different actions or pathways influenced by vasopressin or other substances. For example, increased water reabsorption is primarily a function of vasopressin's action on V2 receptors in the kidneys, leading to water retention in the body. Vasodilation typically involves different mechanisms and agents that relax blood vessels, which contradicts the effect of vasopressin at V1 receptors. An increase in heart rate is more directly influenced by adrenergic stimulation rather than the vasopressor actions of vasopressin. Understanding the distinct functions of vasopressin at its receptor subtypes