Cholinergic and Anti-Cholinergic Drugs

Cholinergic & Anticholinergic Effects on the Parasympathetic Nervous System

Welcome to this video tutorial on cholinergic & anticholinergic drugs and their effects on the parasympathetic nervous system.
First we will take a look at the different divisions of the nervous system.

The nervous system is made up of the central nervous system (the brain & spinal cord) & the peripheral nervous system (neurons outside the brain & spinal cord).
peripheral nervous system is then divided into the autonomic & somatic nervous system.

The autonomic system is further broken down into the sympathetic & parasympathetic nervous system.

The sympathetic (SNS) & parasympathetic (PSNS) are opposing systems.

   The SNS is the “fight or flight” response
AKA – arousing or adrenergic
The PSNS is the “rest & digest” response
AKA – calming or cholinergic

When the SYMPATHETIC system excites an organ, the PARASYMPATHETIC system inhibits it and when the PARASYMPATHETIC system excites an organ, the SYMPATHETIC system inhibits the action.

*Our focus in this lesson is on how cholinergic & anticholinergic agents affect the parasympathetic nervous system.

CHOLINERGIC AGENTS
– Drugs that stimulate the parasympathetic system
– Also called parasympathomimetics – they mimic the effects of the PSNS neurotransmitter
– Cholinergic agents copy the action of acetylcholine (ACh) – a neurotransmitter released from nerve endings that bind on the receptors of cell membranes of organs, tissues & glands

                        There are 2 types of cholinergic drugs:
1. Direct-acting
2. Indirect-acting

Direct-acting cholinergic drugs bind to cholinergic receptors on specific effector organs, stimulating the organ in a similar way as ACh.

– They are synthetic derivatives of choline.

– Have widespread systemic effects including cardiac muscle, smooth muscle, exocrine glands, & the eye.

Indirect-acting cholinergic drugs inhibit the enzyme ‘acetylcholinesterase,’ resulting in more ACh available at the receptors.

– These drugs have the added cholinergic effect of improved skeletal muscle tone & strength.

– Indirect-acting cholinergic drugs for Alzheimer’s disease are widely distributed, including to the central nervous system, thus improving cholinergic neurotransmission in the brain.

Effects of cholinergic drugs

CNS – enhanced cognitive functions such as arousal, attention, & memory encoding – treatment for Alzheimer’s disease & dementia
Eye – pupil constriction – for surgery & treatment of glaucoma
GI – smooth muscle stimulant – for post-op abdominal distention or paralytic ileus
GU – urinary bladder stimulant – for post-op or postpartum urinary retention
Musculoskeletal (indirect acting cholinergic drugs) – improve muscle tone & strength – for myasthenia gravis

Too much cholinergic medication can result in overstimulation of the parasympathetic nervous system, causing unwanted side effects.

The acronym SLUDGE-M will help us remember the adverse effects of cholinergic drugs.

Other Adverse Effects of Cholinergic drugs

       ↓ HR and BP
Conduction abnormalities – AV block & cardiac arrest
Headache, dizziness, convulsions
↑ bronchial secretions, bronchospasms

* Overdosing can cause life-threatening problems
* Antidote for cholinergics is the anticholinergic drug atropine

Specific examples of cholinergic drugs

  1. Direct-acting
    • – Bethanechol (Urecholine) – ↑ the tone & motility of the bladder & GI tract (should cause urination within 60 min in a pt with urinary retention).
    • – Pilocarpine (Pilocar) – used to constrict pupils, which ↓ intraocular pressure (glaucoma).
  2. Indirect-acting
    • – Neostigmine (Prostigmin) – given for the diagnosis & treatment of myasthenia gravis – it causes skeletal muscle contractions.
    • – Donepezil (Aricept) – used to treat mild-moderate Alzheimer’s disease – it ↑ ACh in the brain & helps ↑ or maintain memory or learning capabilities (it manages the symptoms, but is not a cure).

Contraindications to using cholinergic drugs

     Asthma
Hyperthyroidism
Peptic ulcer
Coronary artery disease

*Cholinergic drugs can exacerbate these conditions & should be avoided.

Anticholinergic agents
– Drugs that block the action of ACh on the parasympathetic nervous system.
– These cholinergic blocking agents compete with ACh & block it at the receptors in the PSNS – so ACh is unable to bind to the receptor site & cause a cholinergic effect.
– Most anticholinergic drugs interact with muscarinic cholinergic receptors in the brain, secretory glands, heart, smooth muscle, & eye.

Effects of anticholinergic drugs on various systems:

  • -CNS – ↓ muscle rigidity & muscle tremors – Parkinson’s disease
  • -Eye – pupil dilation – for exams or surgery
  • -Salivary & lacrimal glands – ↓ secretion
  • -Heart – ↑ HR
  • -Respiratory -↓ bronchial secretions, dilate bronchial airways, ↓ airway resistance – COPD, asthma.
  • -GI – relax smooth muscle tone of GI tract, ↓ intestinal & gastric secretions, ↓ motility & peristalsis – peptic ulcer disease, and irritable bowel.
  • -GU – antispasmodic effect on smooth muscle – overactive bladder, and incontinence.

Adverse Effects of Anticholinergics

The effect of the drug may be therapeutic, but becomes an adverse reaction if severe or if the drug is given for another purpose or if there is an overdose.
– CNS – excessive stimulation (tremor, restlessness, confusion), followed by excessive CNS depression (respiratory depression, coma)
– Tachycardia
– Constipation (result of decreased GI motility & muscle tone)
– Dry mouth (result of decreased salivation)
– Urinary retention
– Hot, dry skin (due to decreased sweating)
– Blurred vision, dilation of the pupil (pt may need sunglasses)

* The specific antidote for anticholinergic overdose is

Specific Examples of Anticholinergic Drugs

Belladonna alkaloids & derivatives:
Atropine – a naturally occurring belladonna alkaloid, given for bradyarrhythmias (it produces a stimulant effect), also given as an antidote for cholinergic poisoning.
Ipratropium (Atrovent) – causes bronchodilation, used in asthma & COPD.
Scopolamine – given for motion sickness, N/V.

Centrally acting anticholinergics used in Parkinson’s disease:
Benztropine (Cogentin) – Also used to treat dystonic reactions caused by antipsychotic drugs

Urinary antispasmodics – given for overactive bladder:
Oxybutynin (Ditropan)
Solifenacin succinate (VESIcare)

Contraindications to Using Anticholinergic Drugs
Any condition characterized by symptoms that would be aggravated by the drugs (myasthenia gravis, glaucoma, MI)

REVIEW

Cholinergic drugs stimulate the parasympathetic nervous system by copying the action of Ach.
Cholinergic drugs are given for Alzheimer’s disease, glaucoma, paralytic ileus, urinary retention, & myasthenia gravis.
Anticholinergic drugs block the action of ACh on the parasympathetic nervous system.

Anticholinergic drugs are given for Parkinsons’s disease, asthma, COPD, & overactive bladder

Thank you for watching this video tutorial on cholinergic & anticholinergic effects on the parasympathetic nervous system.

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by Mometrix Test Preparation | Last Updated: June 2, 2020