Category: 02. Drugs Acting On Autonomic Nervous System

Sympathomimetic drugs are stimulant compounds which mimic the effects of endogenous agonists of the sympathetic nervous system. The action of sympathomimetic drugs can be classified as direct and indirect action. The direct mode of activating adrenergic receptors involve the mimicking of endogenous molecules through agonist molecules, and the indirect mode of action involve mechanisms of increasing the release, or decreasing…

Adrenergic receptors are the target of many autonomic drugs that act on the sympathetic nervous system. Adrenergic receptors can mainly be classified into 5 types, known as ⍺1, ⍺2, β1, β2, β3. These adrenergic receptors are located in different tissues and stimulate different physiological responses. ⍺1 receptors are mainly located in smooth muscles, activating them result in vasoconstriction and…

The sympathetic nervous system is involved in stimulating the fight-or-flight response of the body. Activating the sympathetic pathway results in physiological effects including the acceleration of heart beat, increase in force of heart contraction, secretion of adrenaline and noradrenaline by the adrenal gland, bronchi relaxation, and the inhibition of peristalsis and gastrointestinal secretions. Neurotransmitters are used to relay neurotransmission in order to bring about these physiological effects. Acetylcholine is a type of neurotransmitter…

The sympathetic nervous system is another target of autonomic drugs. By stimulating or inhibiting the sympathetic nervous system, therapeutic effects can be achieved.

Botulinum toxin A is an example of inhibitors of acetylcholine release, which is a drug for treating overactive bladder. It blocks the release of acetylcholine from the presynaptic neuron and therefore acetylcholine cannot interact with receptors in the postsynaptic neuron to carry on neurotransmission in the parasympathetic nervous system. This results in a decline in contraction of detrusor muscle in the bladder and brings back a normal activity of…

Patients with bradycardia are treated with atropine. Atropine is a muscarinic antagonist, which can obstruct the muscarinic receptor and acetylcholine cannot bind to the receptor for sustaining transmission of nerve signals to the heart through the parasympathetic nervous system. This allows an increase in heart rate. Hyperthermia, dilated pupils and dry mouth are side effects associated with the use of atropine.

Physostigmine is an anticholinesterase drug and it is used in treating glaucoma. For patients with glaucoma, a rise in intraocular pressure is usually found. Physostigmine can block the action of acetylcholinesterase, reducing disintegration of acetylcholine. There is a higher availability of acetylcholine for supporting neurotransmission in the parasympathetic nervous system, which promotes contraction of smooth muscle in the ciliary body. This results in an increase in outflow of aqueous humor by widening Schlemm’s canal and the trabecular meshwork,…

Bethanechol is a muscarinic agonist. It is included in the therapy for underactive bladder with poor contraction of detrusor muscle. Since contraction of detrusor muscle in the bladder is controlled by the parasympathetic nervous system, Bethanechol can bind to muscarinic receptors to stimulate activation of the parasympathetic nervous system and restore contraction of detrusor muscle. A low dose of Bethanechol is often used in treatment as increasing the dose can cause side effects like nausea, diarrhea and headache.

Autonomic drugs are used clinically to treat diseases that are related to the parasympathetic nervous system.

The activation of the parasympathetic nervous system can bring some major physiological effects, such as a rise in glandular secretion, an increase in contraction of smooth muscle, and a reduction in both heart contractility and heart rate. To achieve the above physiological effects, two types of receptors are involved in neurotransmission, namely nicotinic receptors and muscarinic receptors. These two groups of receptors can bind to…