**Core Concept**
Alpha methyldopa is an antihypertensive agent that primarily acts as a central agonist, mimicking the action of clonidine by stimulating alpha-2 adrenergic receptors in the brain, leading to a decrease in sympathetic outflow and subsequent lowering of blood pressure.

**Why the Correct Answer is Right**
Alpha methyldopa is primarily used for the treatment of hypertension. Its mechanism of action involves the inhibition of the enzyme phenylethanolamine N-methyltransferase (PNMT), which is responsible for converting norepinephrine to epinephrine in the adrenal medulla. By inhibiting PNMT, alpha methyldopa reduces the synthesis of epinephrine, thereby decreasing the sympathetic outflow from the central nervous system. This results in a decrease in heart rate, cardiac output, and peripheral vascular resistance, ultimately lowering blood pressure.

**Why Each Wrong Option is Incorrect**
* **Option A:** Alpha methyldopa is not primarily used as a diuretic or a beta-blocker, as it does not directly affect renal sodium reabsorption or cardiac beta-receptors.
* **Option B:** Alpha methyldopa is not primarily used for the treatment of angina pectoris, as it does not directly affect coronary blood flow or myocardial oxygen demand.
* **Option C:** Alpha methyldopa is not primarily used as an anti-arrhythmic agent, as it does not directly affect cardiac ion channels or the electrical conduction system of the heart.

**Clinical Pearl / High-Yield Fact**
Alpha methyldopa is often used as a first-line antihypertensive agent in pregnant women with hypertension, as it has a long history of safe use in this population. However, it can cause a rare but potentially serious side effect called hemolytic anemia in some patients.

**Correct Answer: A. Treatment of hypertension**