Which term describes a receptor activator that stimulates an action?

The term that accurately describes a receptor activator that stimulates an action is "agonist." Agonists are substances that bind to a specific receptor and trigger a physiological response, effectively mimicking the action of a naturally occurring substance. This interaction can lead to the initiation of a specific signaling pathway, resulting in various biological effects depending on the type of receptor and the tissue involved.

In contrast, an antagonist would bind to the same receptor but block or inhibit the response, preventing the normal action from occurring. An inhibitor works in a similar manner by reducing the activity of enzymes or other proteins, but it does not specifically refer to receptor interactions. The term "agonotropic" is not commonly used in pharmacology or pharmacodynamics, making "agonist" the most accurate choice for describing a molecule that stimulates a receptor's action.