What is the primary action of beta-blockers like metoprolol?

Beta-blockers, such as metoprolol, primarily function by blocking the action of catecholamines, like adrenaline, on beta-adrenergic receptors. This blockade results in a reduction in heart rate and blood pressure, which is crucial for managing conditions such as hypertension, heart failure, and certain types of arrhythmias.

By preventing the effects of adrenaline, beta-blockers decrease the heart's workload and oxygen consumption, effectively lowering heart rate and contractility. This mechanism not only helps to alleviate symptoms related to excessive heart activity but also contributes to overall cardiovascular health, making beta-blockers valuable in both acute and chronic treatment situations.

Other choices involve actions that are not characteristic of beta-blockers. For example, increasing heart rate contradicts their primary action, while stimulating bronchodilation and enhancing cardiac output also fall outside their main pharmacological effects. Overall, the role of beta-blockers in reducing heart rate and blood pressure is essential for understanding their therapeutic uses.