Anticholinergics block the muscarinic receptor so that the ACh doesn’t bind to the muscarinic receptor and the receptor doesn’t get stimulated.
Anticholinergic Effects
Anticholinergics will cause all the opposite effects of parasympathomimetics and AChEI’s:
Eyes:
- Mydriasis (pupil dilation)
- Dry Eye (no lacrimation)
- Accommodation for far vision
- Increases intra-ocular pressure (bad for glaucoma)
Digestive tract:
- Decreased saliva production (dry mouth)
- Decreased stomach acid production (good for peptic ulcers)
- Decreased peristalsis (constipation; good for diarrhea)
Other effects:
- Increased heart rate (good for cardiac insufficiency)
- Bronchodilation (good for asthmatics)
- Urinary retention (good for benign prostatic hyperplasia; large prostate)
Again, all these are sympathetic-like effects from acetylcholine not being able to stimulate the muscarinic receptor in the parasympathetic fibers.
Anticholinergic Order of Sensitivity
Anticholinergics have an order of sensitivity. If we wanted to block an anticholinergic receptor, unfortunately we can’t be very selective. For example, if we wanted to affect GI motility, we would be affecting everything else. If we wanted to affect the eye, we’d be affecting secretions as well. What this tells us is that anticholinergics, especially for treating GI motility, have a lot of side effects. Even if we wanted to simply decrease stomach acid, it would also cause dry mouth and that’s the problem with anticholinergic drugs: Side effects are notorious.
- Secretory (saliva, sweat, stomach acid)
- Eye
- Heart
- GI Motility
