Questions
[1] A 62-year-old woman is noted to have open-angle glaucoma. She inadvertently applies excessive pilocarpine to her eyes. This may result in which of the following?
A. Bronchial smooth muscle dilation
B. Decreased gastrointestinal motility
C. Dilation of blood vessels
D. Mydriasis
[2] Muscarinic cholinergic agonists
A. Activate inhibitory G-proteins (Gi)
B. Decrease production of IP3
C. Decrease release of intracellular calcium
D. Inhibit the activity of phospholipase C
[3] Choline esters like carbachol are most likely to cause which of the following adverse effects?
A. Anhydrosis (dry skin)
B. Delirium
C. Salivation
D. Tachycardia (rapid heart rate)
Answers
[1] C. Excessive pilocarpine may initially result in dilation of blood vessels with a drop in blood pressure and a compensatory reflex stimulation of heart rate. Higher levels will directly inhibit the heart rate. In addition, pilocarpine stimulation of muscarinic cholinoreceptors can result in miosis, bronchial smooth muscle dilation, and increased GI motility.
[2] A. In addition to activating inhibitory G-proteins (Gi), muscarinic cholinergic agonists stimulate the activity of phospholipase C, increase production of IP3, and increase release of intracellular calcium.
[3] C. Diarrhea, salivation, and lacrimation may be seen. The heart rate is usually slowed. Choline esters do not cross the blood-brain barrier, and therefore delirium is not an adverse effect.
Pharmacology pearls
Cholinoreceptors are classified as either nicotinic or muscarinic.
Muscarinic cholinoreceptors are localized at organs such as the heart, causing a negative chronotropic effect.
Stimulation of muscarinic receptors in the smooth muscle, exocrine glands, and vascular endothelium cause bronchoconstriction, increased acid secretion, and vasodilation.
Methacholine and bethanechol are highly selective for muscarinic cholinoreceptors.
Cholinomimetic agents, including anticholinesterase inhibitors, are precluded for treatment of gastrointestinal or urinary tract disease because of mechanical obstruction, where therapy can result in increased pressure and possible perforation. They are also not indicated for patients with asthma.
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