- Distinguishing features
- A bush that has large, oblong, smooth leathery evergreen leaves. The flowers, spotted on the inside, form in large showy terminal clusters and can be a variety of colors.
- Rhododendron are large shrubs or small trees with evergreen lanceolate to elliptical leaves and terminal clusters of large, attractive pink to purple flowers.
- Geographic range
- Accidental exposure of foraging animals or pets can occur over much of the United States. The plant does best in well-drained, sandy or rocky soils at elevations above 3000 feet. Some species of this genus are grown as garden or landscape plants (e.g., azaleas), whereas others range wild in the woods and mountain foothills of the southeastern and Appalachian states. Plants generally do not survive in the northern states with very cold winters. Rhodo-dendron also grow in the Pacific coastal states and western British Columbia. Ornamental varieties may be grown extensively in the Midwest.
- Toxic principle
- Andromedotoxins (grayanotoxins) are water-soluble diterpenoid compounds. Leaves and flower nectar (including honey made from plant nectar) are sources of the toxin.
- As little as 3 ml nectar/kg body weight or 0.2% of the body weight as leaves may be toxic or lethal.
- Mechanism of toxicologic damage
- Andromedotoxins (grayanotoxins) bind to and modify the sodium channels of cell membranes, leading to prolonged depolarization and excitation. Modification of the sodium channels favors calcium movement into cells and results in a positive inotropic effect similar to that of digitalis.
- Clinical signs
- Salivation and a burning sensation in the mouth are followed by emesis, diarrhea, muscular weakness and impaired vision. Bradycardia, hypotension (caused by vasodilation) and atrioventricular block are serious cardiovascular effects that may be lethal. Dyspnea, depression, and prostration develop, and death may occur within 1-2 days. Ruminants often bloat. Aspiration pneumonia can develop secondary to emesis.
- Laboratory diagnosis
- Generally non-specific findings.
- Lesions are non-specific
- Detection of leaves in GI tract may assist in diagnosis.
- Detoxification. Emesis is used where appropriate. Activated charcoal should be administered repeatedly the first day.
- Supportive therapy. Fluid replacement therapy and respiratory support may be necessary. Atropine is recommended for severe bradycardia. Isoproterenol or sodium channel blockers (e.g., quinidine) may be used to treat heart block.
Honey made from the plants has been reported to cause cardiac arrhythmias, emesis, mild paralysis and convulsions in humans and is known as “mad honey”.
Read more in the Poisonous Plants of Pennsylvania Publication