response. However, the enzyme acetylcholinesterase can inactivate the acetyl-
choline before it reaches the receptor cell.
Drugs that mimic acetylcholine are cholinergic agonists because they initiate
a response. These are also known as cholinergic drugs or parasympathomimet-
ics (see chart).
Drugs that block the effect of acetylcholine are called anticholinergic, or
parasympatholytics. They are also known as cholinergic antagonists because
they inhibit the effect of acetylcholine on the organ.
There are two types of cholinergic receptors. These are nicotinic or mus-
carinic. Nicotinic receptors are stimulated by alkaloids nicotine. Muscarinic
receptors are stimulated by muscarine.(^282) CHAPTER 15 Nervous System Drugs
Receptor Physiologic responses
Alpha 1 Increases force of contraction of heart. Vasoconstriction: increases blood pressure.
Mydriasis: dilates pupils of the eyes. Glandular (salivary): decreases secretions.
Bladder & prostate: capsule increases contraction and ejaculation.
Alpha 2 Inhibits the release of norepinephrine, dilates blood vessels, and produces hypoten-
sion; decreases gastrointestinal motility and tone.
Beta 1 Increases heart rate and force of contraction; increases rennin secretion, which
increases blood pressure
Beta 2 Dilates bronchioles; promotes GI and uterine relaxation; promotes increase in blood
sugar through glycogenolysis in the liver; increases blood flow in the skeletal muscles.
Sympathetic Stimulants Parasympathetic Stimulants
Sympathomimetics (adrenergics,
adrenomimetics, or adrenergic agonists)
Increase blood pressure
Increase pulse rate
Relax bronchioles
Dilate pupils of eyes
Uterine relaxation
Increase blood sugar
Direct-acting
Parasympathomimetics (cholinergics, or
cholinergic agonists)
Decrease blood pressure
Decrease pulse rate
Constrict bronchioles
Constrict pupils of eyes
Increase urinary contraction
Increase peristalsis
Indirect-acting
Cholinesterase Inhibitors (anticholinesterase)
Increase muscle tone