What best describes the mechanism of action of ephedrine?

The chosen answer describes the mechanism of action of ephedrine accurately by encompassing its dual action. Ephedrine acts directly on the postsynaptic alpha and beta adrenergic receptors, which contributes to its sympathomimetic effects such as increasing heart rate and bronchodilation.

Additionally, ephedrine has an important indirect action: it stimulates the release of norepinephrine (NE) from presynaptic nerve terminals. This results in an increased level of norepinephrine available to bind to adrenergic receptors, thereby enhancing its overall adrenergic effect. The combination of these direct and indirect mechanisms allows ephedrine to exert a more potent effect on the cardiovascular and respiratory systems compared to a drug that only works through one of these pathways.

Understanding this dual mechanism is crucial in pharmacology, as it highlights why ephedrine is often used in clinical settings for conditions that require both bronchodilation and increased blood pressure. The presence of both actions ensures that ephedrine remains effective across various physiological scenarios.