Question

1. State the responses that a muscarinic agonist would be expected to cause through direct activation of muscarinic cholinergic receptors (consider bethanechol). The student should focus on the main “targets” of parasympathetic nervous system activity: eyes, respiratory system, heart and blood vessels, gastrointestinal (GI) and urinary tracts, and the secretory activity of exocrine glands (e.g., lacrimal, mucous, and so on).

2. List cholinergic responses not normally caused when the usual therapeutic doses of a muscarinic agonist are administered and explain why these effects do not occur.

3. State the main side effects of a muscarinic agonist (for example, bethanechol) and related precautions or contraindications to its use.

4. Give several reasons why acetylcholine itself is not used to produce selective muscarinic-activating effects and why other drugs generally are chosen.

5. Describe the signs and symptoms of muscarinic antagonist (for example, atropine) “poisoning,” how it is managed, and how and where such a syndrome can occur without the patient receiving any therapeutic product.

Answer 1

1. Muscarinic receptors stimulate the parasympathetic system on the target organs. Bethanechol is the choline esters which acts directly on muscarinic receptors.

• When it acts on the eyes, it produces the effect of miosis(constriction of the pupil) and myopia(constriction of ciliary muscle).
• In the respiratory system, it acts on the smooth muscle of the lungs and causes constriction of bronchi.
• Muscarinic receptors act on the heart and lead to bradycardia.
• Muscarinic activates on the bladder causes contraction of detrusor muscle results in relaxation of sphincter for the emptying of the bladder.
• In blood vessels, muscarinic act results in vasodilation and leads to hypotension.
• It acts on the smooth muscles of the GI tract and increases motility and agonists produce GI contraction.
• It acts on the exocrine gland and increases the salivary secretions, bronchial secretions, gastric acid secretion, and sweats.

3. The main side effects of muscarinic agonists are

• Hypotension
• Asthma
• Bradycardia
• Excessive secretion of saliva
• GI cramps
• Diarrhea
• Urinary urgency.

5. Muscarinic poisoning is the results of an overdose of muscarinic. Atropine reverses the poisoning of the muscarinic agent by blocking the muscarinic receptors. Muscarinic poisoning also occurs by intake of certain mushrooms excessively. The signs and symptoms include

• blurred vision
• dry mouth
• hallucinations
• photophobia
• hyperthermia
• delirium
• hot flush skin
• respiratory depression.