19. Agents and Actions of the Autonomic Nervous System: Autonomic Pharmacology Overview

Autonomic Pharmacology Overview

Autonomic Nervous System

Composed of the sympathetic and parasympathetic nervous systems. Adrenergic activators activate the sympathetic system whereas cholinergic activators activate the parasympathetic nervous system.

Adrenergic Activators

(Sympathomimetics)
Adrenergic activators are agonists that stimulate adrenergic receptors resulting in stimulation of the sympathetic nervous system (fight or flight). Adrenergic receptors are located on a variety of organs that have predictable responses based on the receptor type that is stimulated. This will be reviewed in more depth in the next section.

Adrenergic Antagonists

(Symptholytics)
Adrenergic antagonist block adrenergic receptors preventing activation of the sympathetic nervous system resulting in parasympathetic-like efforts.

Cholinergic Activators

(Parasympathomimetics)
Cholinergic activators are agonists that stimulate cholinergic receptors resulting in stimulation of the parasympathetic nervous system (rest and digest). Similar to adrenergic receptors, cholinergic rectors are located on a variety of organs that also have predictable responses based on the receptor type that is stimulated. This will also be reviewed in more depth in the next section.

Cholinergic Antagonists

(Parasympathomimetics)
Cholinergic antagonists block adrenergic receptors prevent activation of the sympathetic nervous system resulting in sympathetic-like effects.

Effects of Adrenergic Agonists & Antagonists and Cholinergic Agonists & Antagonists on Various Organs

As mentioned about, organs innervated by the autonomic nervous system have predictable responses when specific receptors are stimulated or blocked. Below is a summary of the key organs and their responses to both adrenergic and cholinergic receptor agonists and antagonists.

Digestive System

As show below on the right, adrenergic agonists result in relaxation of GI smooth muscle, contraction of sphincters and decreased GI secretions. All of these actions prevent digestion and defecation. *Note that cholinergic ANTAGONISTS result in the same actions.

As shown below on the left, cholinergic agonists result in contraction of GI smooth muscle, relaxation of sphincters and increases GI secretions. All of these actions promote digestion and defecation. *Note that adrenergic ANTAGONIST result in the same actions.

Eyes

As shown below on the right, adrenergic agonists result in pupil dilation, also known as mydriasis, and ciliary muscle relaxation enhancing far vision. *Note that cholinergic ANTAGONISTS result in the same actions.

As shown below on the left, colinergic agonists result in pupil constriction, also known as meiosis, and ciliary muscle contraction enhancing near vision. *Note that adrenergic ANTAGONIST result in the same actions.

Heart

As shown below on the right, adrenergic agonists result increases heart rate and increased cardiac output. Both of these actions will enhance oxygen delivery throughout the body as it is in high demand when in “fight or flight” situations. *Note that cholinergic ANTAGONISTS result in the same actions.

As shown below on the left, cholinergic agonists result in decreased heart rate and decreased cardiac output. Both of these actions reduce oxygen delivery throughout the body as it is not in high demand when “resting and digesting.” *Note that adrenergic ANTAGONIST result in the same actions.

Lungs

As shown below on the right, adrenergic agonists result in bronchodilation allowing for increased oxygen intake essential in “fight or flight” situations. *Note that cholinergic ANTAGONISTS result in the same actions.

As shown below on the left, cholinergic agonists result in bronchoconstriction decreasing oxygen intake. Oxygen is not as in high demand when “resting and digesting.” *Note that adrenergic ANTAGONIST result in the same actions.

Urinary Bladder

As shown below on the right, adrenergic agonists result in relaxation of the detrusor muscle and contraction of the internal sphincter. These actions prevent urination. *Note that cholinergic ANTAGONISTS result in the same actions.

As shown below on the left, cholinergic agonists result in contraction of the detrusor muscle and relaxation of the internal sphincter. These actions promote urination. *Note that adrenergic ANTAGONIST result in the same actions.