Chapter 90 Anticholinergic Poisonings
INTRODUCTION
Neurotransmission within the autonomic nervous system may be divided functionally into the sympathetic and parasympathetic systems, or chemically into the adrenergic and cholinergic systems. The cholinergic division consists of all synapses at which acetylcholine is the chemical mediator released. The cholinergic portion of the autonomic nervous system consists of: (1) all preganglionic neurons in the sympathetic and parasympathetic systems, (2) all postganglionic neurons of the parasympathetic system, (3) postganglionic sympathetic neurons that innervate sweat, salivary, lacrimal, and nasopharyngeal glands, and (4) postganglionic sympathetic neurons that innervate skeletal muscle and blood vessels and induce vasodilation when stimulated. The responses of various effector organs to cholinergic stimulation are shown in Table 90-1. Generally, cholinergic neurons can be considered those responsible for an anabolic or vegetative state, stimulating digestion, decreasing cardiac work, and relaxing vascular smooth muscle.
Table 90-1 Responses of Effector Organs to Cholinergic Stimulation
| Effector Organs | Cholinergic Response |
|---|---|
| Ophthalmic | |
| Iris sphincter | Contraction (miosis) |
| Ciliary muscle | Contraction (near vision) |
| Cardiac | |
| SA node | Decrease heart rate |
| Atria and ventricles | Decrease contractility |
| AV node and His-Purkinje system | Slow conduction |
| Vascular | |
| Coronary, skin, mucosa, skeletal muscle, cerebral, pulmonary, salivary arterioles | Dilation |
| Systemic veins | No effect |
| Pulmonary | |
| Bronchioles | Constriction |
| Bronchial glands | Secretion |
| Gastrointestinal | |
| Motility and tone | Increase |
| Mucous glands | Secretion |
| Pyloric sphincter | Increase tone |
| Intestinal sphincters | Decrease tone |
| Gall bladder and ducts | Contraction |
| Urinary | |
| Detrusor | Contraction |
| Trigone and sphincter | Relaxation |
| Ureter motility and tone | Increase |
| Endocrine / Glandular | |
| Adrenal medulla | Secretion of epinephrine and norepinephrine |
| Pancreatic acini and islet cells | Increase secretion |
| Salivary, lacrimal and nasopharyngeal glands | Increase secretion |
AV, Atrioventricular; SA, sinoatrial.
Modified from Brunton LL: Goodman & Gilman’s the pharmacological basis of therapeutics, ed 11, New York, 2005, McGraw-Hill.
Many plants contain anticholinergic compounds, as do numerous drugs. Box 90-1 contains a listing of plants and drugs that can cause anticholinergic toxicity.1 The drugs are further divided into those in which anticholinergic activity causes the primary toxic effect and those in which anticholinergic effects occur but other toxic effects are more likely to be life threatening. Although exposure to toxic plants with anticholinergic effects is less common in small animals than in large animals, case reports of natural exposures exist.2 The classes of drugs most commonly associated with anticholinergic toxicity in small animals include antihistamines (e.g., diphenhydramine) and tricyclic antidepressants (e.g., amitriptyline, clomipramine). In addition, it is important to assess the possibility of exposure to human medications, such as anti-Parkinsonian drugs and antinausea medications (e.g., promethazine).
