Functions of the Parasympathetic Nervous System
- Slowing of HR
- Increased gastric secretion
- Emptying of the bladder
- Emptying of the bowel
- Focusing the eye for near vision
- Constricting the pupil
- Contracting bronchial smooth muscle
Sites of drug action in the PSNS
- The synapses between preganglionic neurons and postganglionic neurons
- The junctions between postganglionic neurons and their effector organs
What neurotransmitter is associated with the PSNS?
Acetylcholine (preganglionic and postganglionic neurotransmitter)
Function of cholinergic receptors
Mediate response to acetylcholine
Three subtypes of cholinergic receptors
Muscarinic, NicotinicM, NicotonicN
Activation of NicotinicN (neuronal) receptor
Promotes ganglionic transmission, promotes release of norepinephrine from adrenal medulla
Activation of Nicotinic M (muscle) receptor
Causes contraction of skeletal muscle
Activation of Muscarinic receptor
located on target organs, binding causes organ response
Drugs that stimulate the PSNS receptors are called…
Stimulants, agonists, cholinergic drugs
Drugs that block the PSNS receptors are called…
Blockers, antagonists, anticholinergic drugs
Excess cholinergic effects
- Decreased intraocular pressure (cholinergic drugs are used to treat glaucoma)
- Mitosis (constriction of pupil)
- Sweating - WET
- Increased salivation
- Increased bronchial secretions – increased risk for pneumonia or other respiratory infections
- Bronchial constriction – increased risk for asthmatic patients
- Increased GI tone
- Diarrhea
- Decreased blood pressure
- Bradycardia
- Contraction of bladder detrusor muscle
Excess anticholinergic effects
- Increased intraocular pressure
- Mydriasis (dilation of pupils)
- Photophobia – light sensitivity
- Decreased sweating – fluid and electrolyte issues
- Dry mouth
- Decreased bronchial secretions
- Respiratory depression
- Decreased GI motility with possible constipation
- Decreased BP (compensatory mechanism for tachycardia) followed by increased BP
- Tachycardia and, possibly, palpitations
- Urinary retention
- Vasodilation
- Drowsiness, confusion, and agitation – elderly are at risk
Anticholinergic Poisoning
- Mad as a hatter
- Blind as a bat
- Red as a beet
- Dry as a bone
Pilocarpine
Direct-acting cholinergic – agonist, stimulates acetylcholine directly
Pilocarpine is typically used for…
- Topical pharmacotherapeutics
- Simple and acute glaucoma
- Preoperative and postoperative elevated intraocular pressure
- Drug-induced mydriasis
Nicotine
- Stimulates the CNS
- Pharmacotherapeutics are limited to preparations to assist in smoking cessation
- Adverse effects are related to its effects on the cardiovascular system (tachycardia, hypertension) and CNS
- If a person has had a cigarette within a 30-minute timeframe of taking his/her blood pressure, it will be elevated – after 30 minutes; the blood pressure should come back to normal
Neostigmine
- Indirect-acting cholinergic drug
- Acts by reversibly inhibiting postsynaptic cholinesterase (enzyme that degrades acetylcholine)
- Used in the treatment of myasthenia gravis to minimize muscle fatigue
- Most serious adverse effect: cholinergic crisis
Atropine
- Anticholinergic drug
- Antidote to cholinergic poisoning
- Pharmacotherapeutics:
- Preoperatively to dry secretions
- Acute cardiac emergencies
- Topically (homatropine) to treat ophthalmic disorders
- Treatment of motion sickness and diarrhea (Lomotil) - Adverse effects related to loss of acetylcholine stimulation on receptors
- Most serious adverse effect: Anticholinergic overdose (poisoning)
