**Core Concept:** Adrenaline (epinephrine) is a catecholamine hormone and neurotransmitter that plays a crucial role in the body's physiological responses to stress, including increased heart rate and blood pressure, bronchoconstriction, and stimulation of glycogenolysis and gluconeogenesis in the liver. Prazosin is a selective alpha-1 blocker, while propranolol is a non-selective beta-blocker.

**Why the Correct Answer is Right:** Prazosin is a selective alpha-1 receptor antagonist, meaning it binds to alpha-1 receptors and blocks their activity. In the context of adrenaline, this blocks the vasoconstrictor effects on blood vessels, counteracting the increased blood pressure and heart rate induced by adrenaline.

Adrenaline binds to beta-1 receptors in the heart, leading to increased heart rate and contractility. Propranolol is a non-selective beta-blocker, meaning it binds to beta-1 receptors and blocks their activity. As a result, propranolol does not reverse the effects of adrenaline.

**Why Each Wrong Option is Incorrect:**

A. Prazosin's selectivity for alpha-1 receptors makes it incorrect for counteracting adrenaline's effects on beta-1 receptors.
B. Propranolol's non-selectivity for alpha-1 receptors makes it ineffective in counteracting adrenaline's vasoconstrictor effects.
C. Adrenaline's actions are mediated by both alpha and beta receptors, making a single drug, like atenolol (beta-blocker), insufficient for counteracting its effects.
D. While propranolol is a beta-blocker, its non-selectivity makes it an incorrect choice for specifically targeting adrenaline's effects on beta-1 receptors.

**Clinical Pearl:** Understanding the selectivity of drugs like prazosin and propranolol is crucial for selecting appropriate treatments in various clinical scenarios, such as hypertension, angina, and heart failure.

**Correct Answer:** C. Adrenaline

**Explanation:** Adrenaline's effects are primarily mediated by beta-1 receptors in the heart and alpha-1 receptors in the blood vessels. Prazosin (alpha-1 blocker) would be effective in counteracting adrenaline's vasoconstrictor effects on blood vessels, but not in preventing adrenaline's effects on the heart. Atenolol (beta-blocker) would be effective in counteracting adrenaline's effects on both heart and blood vessels, making it an appropriate choice for treating hypertension and angina.