Page 263 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

230 SECTION | II Organ Toxicity

VetBooks.ir apparent after several hours postingestion (Sharma et al., acid formed by a plant varies, but the lethal dose for a
mouse is 3.7 mg/kg b.w., and for cattle and sheep, it is
2009). Cardiovascular symptoms include hypotension,
2.0 mg/kg b.w. (Speijers, 2003). Plants containing CG in
cardiac arrhythmias, and weak heart rate. The severity of
toxicity also depends on the route of exposure. The LD 50 excess of 20 mg/100 mg of plant material are avoided in
in mice is 5.1 mg/kg b.w. (Barceloux, 2008). Treatment is feedstock.
symptomatic. Ruminant animals are more likely to be poisoned than
Kalmia spp. (Laurel, Lambkill) is an evergreen shrub monogastric animals (horses and pigs) because the lower
of the family Ericaceae, native to North America. The pH in the stomach of monogastric animals destroys
plant contains the glycoside grayanotoxin that is toxic to enzymes that change CG to hydrocyanic acid. Antidotes
ruminants. The LD 50 in rats is 2 5 mg/kg b.w. (Frohne include sodium nitrate and sodium thiosulfate
and Pfander, 2005). Minimum toxic dose in cattle is 0.4% (Table 14.2).
b.w. (Beasley, 1999).
A grayanotoxin, also known as acetylandromedol,
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binds to Na ion channel receptors involved with activa- ALKALOID-CONTAINING PLANTS
tion and inactivation of the cells. With inactivation
blocked, the excitable cells remain depolarized. Cardiac Delphinium spp. (Larkspur) consists of 250 species of
symptoms include low blood pressure, bradycardia, and annual and biennial flowering plants of the buttercup fam-
also ventricular tachycardia (Jansen et al., 2012). ily Ranunculaceae, distributed throughout the Northern
Therapy includes atropine and also vasopressors to Hemisphere. Their ingestion by livestock has been
raise the blood pressure. Arrhythmias produced by graya- responsible for extensive losses of cattle (Green et al.,
notoxin I can be reversed by tetrodotoxin (Akera et al., 2009). The plant contains numerous norditerpenoid alka-
1976; Ku et al., 1977). loids of the lycoctonine and the MDL (7,8-methylene-
Kalanchoe spp. (Mother of Millions, Chandelier Plant) dioxylycoctonine) and MSAL (methylsuccinyl
are perennial plants that can be forced to bloom at any anthranoyllycoctonine) type. Among the lycoctonine are
time of year. It is a genus of nearly 200 plant species three MSAL-type (potent neuromuscular poisons acting
native to Africa but now also found in Florida and on the postsynaptic neuromuscular junction), extremely
Hawaii. Since they contain cardiac glycosides, they affect toxic neuromuscular blocking agents. MSAL-type alka-
the heart by altering the electrolytic balance in the myo- loids, the MLA (methyllycaconitine), DAN (nudicauline),
cardium. In the wild, these plants are apt to poison sheep and 14-DAN (14-deacetylnudicauline) cause most of the
and cattle although household animals are also suscepti- cattle poisonings from Larkspurs (Pfister et al., 1999).
ble. The lethal dose for leaves of the plant for calves has MSAL-type alkaloids are found to be 20 times more toxic
been determined to be 40 g/kg b.w. The toxicity is due to than MDL type in mice (Panter et al., 2002; Welch et al.,
the bufadienolide compounds, which are cardiac glyco- 2008). LD 50 is 25 40 mg/kg b.w. depending on the type
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sides that inhibit the Na /K -ATPase pump of the myo- of alkaloid present.
cardial cell membrane (Smith, 2012). Recommended Intoxication occurs when the nicotinic acetylcholine
treatment for toxicosis is symptomatic and supportive. receptors are blocked. There are species differences in the
symptoms, but the usual cardiac signs include rapid and
irregular heartbeat and hypotension. The effect of
CYANIDE-CONTAINING PLANTS
Larkspur-derived MSAL alkaloids are counterbalanced by
Approximately 2500 plants contain cyanogenic glycosides neostigmine or physostigmine. AChE inhibitors alleviate
(CG) (Vetter, 2000). Hydrocyanic acid/prussic acid is the clinical symptoms in cattle (Green et al., 2009).
commonly formed in the seeds and leaves of sorghum Physostigmine given i.v. at the rate of 0.08 mg/kg b.w.
plants and also from Cassava. Cyanide is a rapidly acting has been used under field conditions to relieve symptoms,
poison that inhibits the action of cytochrome oxidase that though it may need to be repeated.
links oxygen with erythrocytes. Plants with only 20 mg of Aconitum spp. (Monkshood) is an herbaceous peren-
CG per 100 g (Allison and Baker, 2007) can kill livestock nial found in elevated regions of the Northern
by asphyxia. By inhibiting cytochrome oxidase, cyanide Hemisphere. Even though, all parts of the plant are poi-
induces cellular hypoxia. Since oxygen cannot be utilized, sonous and contain polycyclic diterpene alkaloids with
adenosine triphosphate is no longer formed. Cardiac affinity for the open state of the voltage-sensitive sodium
symptoms include tachycardia, dysarrhythmia, and pete- channel making them refractory to excitation (Chan,
chial hemorrhage of the heart and other organs. ECG 2009). Aconite causes anticholinergic effects and has a
changes include elevation or depression and shortened positive inotropic effect by a prolonged influx of sodium.
ST-segment, as well as fusion of the T-wave and QRS LD 50 for mice for aconite is 130 280 mg/kg b.w.
segment (Holstege et al., 2010). The amount of hydrocyanic depending on the plant. Aconite causes hypotension,