Agonists

Definition

Agonists are substances that bind to and activate specific receptors in the body, mimicking the effects of the natural ligand or endogenous substance that normally binds to that receptor. They initiate a physiological response by triggering the receptor's signaling pathways.

5 Must Know Facts For Your Next Test

1. Agonists can be endogenous (naturally occurring) or exogenous (synthetic or drug-derived) substances that bind to and activate a specific receptor.
2. The binding affinity and efficacy of an agonist determine the magnitude of the physiological response elicited at the receptor.
3. Agonists can have different degrees of selectivity, binding to and activating specific receptor subtypes or a broader range of receptor types.
4. The therapeutic effects of many drugs are achieved through the activation of specific receptor agonists, such as opioid agonists for pain relief or adrenergic agonists for cardiovascular support.
5. Receptor desensitization and downregulation can occur with chronic exposure to agonists, leading to a diminished physiological response over time.

Review Questions

• Explain how agonists interact with receptors to elicit a physiological response.
  • Agonists bind to and activate specific receptors in the body, mimicking the effects of the natural ligand or endogenous substance that normally binds to that receptor. This binding triggers the receptor's signaling pathways, initiating a physiological response. The binding affinity and efficacy of the agonist determine the magnitude of the response, with higher affinity and efficacy leading to a more potent activation of the receptor and a greater physiological effect.
• Differentiate between full agonists, partial agonists, and inverse agonists, and describe how their interactions with receptors can lead to different physiological outcomes.
  • Full agonists bind to and activate receptors, eliciting the maximal physiological response. Partial agonists also bind to and activate receptors, but with less than the maximal effect of a full agonist, resulting in a submaximal response. Inverse agonists, on the other hand, bind to and activate a receptor in the opposite way to an agonist, inducing a physiological response that is the reverse of the agonist's effects. The type of agonist-receptor interaction can significantly impact the overall physiological outcome, with full agonists typically producing the strongest effects, partial agonists producing moderate effects, and inverse agonists potentially counteracting the effects of endogenous agonists.
• Analyze the role of agonists in pharmacological interventions and discuss the potential implications of receptor desensitization and downregulation in the context of chronic agonist exposure.
  • Agonists play a crucial role in many pharmacological interventions, as the activation of specific receptors by agonists can elicit desired therapeutic effects, such as pain relief, cardiovascular support, or the management of various medical conditions. However, chronic exposure to agonists can lead to receptor desensitization and downregulation, where the receptors become less responsive to the agonist over time. This can result in a diminished physiological response, potentially reducing the effectiveness of the pharmacological intervention. Clinicians must consider the potential for receptor desensitization and downregulation when prescribing medications that rely on agonist-receptor interactions, and may need to adjust dosing or explore alternative treatment strategies to maintain the desired therapeutic effects.

Related terms

Antagonists:

Antagonists are substances that bind to and block receptors, preventing the natural ligand or agonist from binding and activating the receptor, thereby inhibiting the receptor's physiological effects.

Partial Agonists: Partial agonists are substances that bind to and activate a receptor, but with less than the maximal effect of a full agonist, resulting in a submaximal physiological response.

Inverse Agonists: Inverse agonists are substances that bind to and activate a receptor in the opposite way to an agonist, inducing a physiological response that is the reverse of the agonist's effects.