9. Toxicants Affecting the Cardiac & Respiratory Systems I

What is seen with acute toxicity of the heart?

arrhythmia and decreased cardiac function

What is seen with chronic toxicity of the heart?

hypertrophy (eccentric) and malignant arrhythmia

carboxylic polyether antibiotic that is isolated from streptomyces cinnamonensis given as a feed additive and coccidiostat

ionophores

What is an example of an ionophore?

monensin

What species is very sensitive to ionophores?

horses

What does ionophore toxicity cause in horses?

P
R
V
A

• prolonged depolarization

• repolarization

• V-tach

• AV block

What does ionophore toxicity cause in cattle?

Q
F
M

• OT, ORS prolongation

• first degree AV block

• muscle damage

Which species are the least sensitive to ionophore toxicity?

cattle

What is ionophore toxicity often the result of? How much over target is it often?

mixing error at feed mill; 10X over target

tri-aza-pentadiene compound used in flea collars of dogs and as an insecticide and acaricide

amitraz

How does amitraz exert toxicity?

inhibits the enzyme monoamine oxidase (MAO) and works as an a2 adrenergic receptor agonist

What are the cardiac effects of a2-adrenergic agonists?

B
F
D

• bradycardia

• first and second degree atrioventricular blockage

• diminshed cardiac output

What is the toxic component of blister beetles? What does it inhibit?

cantharidin; serine-threonine protein phosphatase

How does cantharidin cause toxicity?

blocks adenosine A1 receptors, which regulate myocardial O2 consumption, yielding anti-adrenergic effect in ventricular cardiac myocytes

What are cardiac symptoms associated with cantharidin poisoning?

I
M
C

• increased heart rate

• myocardial dysfunction

• colic in horses

What respiratory signs are seen with cantharidin poisoning? Why do they occur?

thumps; diaphragmatic contractions due to hypocalcemia

What are signs associated with bufo toad toxicities?

P
V
P
R

• profuse, sometimes frothy salivation

• vigorous head shaking

• pawing at the mouth

• retching

What toxin is associated with bufo toads?

bufotoxin

mix of steroid lactones that include glycosides (bufadienolides) as well as epinephrine, norepinephrine, and serotonin

bufotoxin

What secretes bufotoxin in the bufo toads?

parotoid glands

What is the treatment for bufotoxin?

decontamination (wash out the dog’s mouth)

What is the toxic principle of foxglove digitalis spp?

digitalis glycosides

What parts of the foxglove digitalis contain the toxic compound? Are fresh or dry material toxic?

all parts; both

Where is digitalis glycosides absorbed from? How is it eliminated?

GI tract; hepatic metabolism and in the urine

What is the half-life of digitalis glycosides in dogs?

16-40 hours

When do GI signs associated with foxglove digitalis spp occur?

prior to CV signs

What are the GI signs involved with foxglove digitalis spp?

A
C
D

• anorexia

• colic

• diarrhea

What is the mechanism of toxicity of foxglove digitalis spp? What does this primarily result in?

inhibition of Na-K pump; intracellular calcium imbalance and cardiac rhythm disturbances

Blood levels of what value of digitalis glycosides are toxic in dogs?

> 3 ng/mL

What are the symptoms of digitalis cardiac toxicity?

S
A
A
D

• sinus bradycardia and arrest

• AV block (usually 2nd degree

• atrial tachycardia with AV block

• development of junctional rhythm PVCs

What are the toxic principles in milkweed asclepias spp?

cardenolides (similar to digitalis glycosides) and galitoxin (a resinoid)

Depending on the animal and plant, when do symptoms of milkweed toxicity usually begin to appear?

within hours

The mechanism of toxicity of milkweed asclepias spp is the same as what?

foxglove

What is the toxic dose of milkweed?

0.1%-0.5% of the animal’s body weight

What are the clinical signs associated with milkweed toxicity?

A
D
W
L
C
S

• ataxia

• depression

• weakness

• labored breathing

• cardiac arrhythmias

• seizures

What are the toxic principles of oleander nerium spp? Specifically which ones?

cardiac glycosides; oleandrin and neriine

True or false: All parts of the Oleander plant contain the toxic components. The red flowers are reported to be the most toxic and both fresh and dry material contains the toxins.

true

Oleander appears to be readily absorbed from where?

the GI tract

Within what time frame can a large dose of oleander be fatal in? When do symptoms usually appear?

1 hour; 24 hours

Oleander toxins are detected in ________.

milk

What is the toxic principle of lilly of the valley (convallario majalis)?

convallotoxin (cardiac glycoside)

What is the mechanism of toxicity of oleander?

same as goxglove

What are the clinical signs associated with oleander toxicity?

same as foxglove

How is the diagnose of oleander toxicity made?

same as foxglove

What is the treatment for oleander toxicity?

same as foxglove

What is the toxic principle of lily of the valley? Which one specifically?

cardiac glycosides; convallotoxin

True or false: All parts of the lily of the valley plant contain the toxic components. The red berries appearing in the spring may be the most toxic.

true

What is the toxic principle of the azalea rhododendron spp?

grayanotoxin

Where is the toxic component of azaleas found?

in the honeys from the nectar of the plant

What is the duration of effects of azalea toxicity?

1 to 2 days

What is the mechanism of toxicity for azaleas?

bind to voltage gated sodium channels producing depolarization

What are the clinical signs associated with azalea toxicity?

D
E
V
B
A
S

• depression

• excess salivation

• vomiting

• bradycardia

• arrhythmias

• seizures

True or false: Mountain laurel is poisonous to several different animals, including horses, goats, cattle, deer, and humans. The green parts of the plant, flowers, twigs, and pollen are all toxic.

true

What is the toxic principle of mountain laurel and sheep laurel?

grayanotoxins

What is the mechanism of toxicity of mountain laurel and sheep laurel?

bind to voltage gated sodium channel producing depolarization

What are the clinical signs associated with mountain laurel and sheep laurel toxicity?

E
P
V
D
W
P
L
S

• excessive salivation

• perspiration

• vomiting

• dizziness

• weakness

• paresthesia in the extremities and around the mouth

• low blood pressure

• sinus bradycardia

What is the toxic principle of avocado persea americana?

persin

What part of the avocado is documented to be harmful to animals?

leaves, dark, skin, and pit

What species are particularly sensitive to avocado toxicity? What does it cause in these species?

birds and horses; myocardial necrosis

What is the toxic principle of kalanchoe species?

bufadienolides

What is the mechanism of toxicity of the kalanchoe species?

similar to digitalis

When will clinical signs of kalanchoe species toxicity occur in dogs?

after consumption of 7 mg/kg

What are the toxic principles found in dogbane (indian hemp)?

apocynin and cymarin

What species are most often affected by dogbane toxicity?

sheep

What is the major toxic ingredient in the cotton plant?

gossypol

What can prolonged exposure to gossypol cause? What other systems may also be affected?

acute heart failure resulting from cardiac necrosis; hepatic, renal, and reproductive

What species are more often affected by cotton plant toxicity?

monogastrics (horses)

True or false: All parts of the yew taxus spp are toxic except the aril encapsulating the seed. Upon rumen examination, you will usually find leaves.

true

What is the toxic principle in the yew taxus spp?

taxine alkaloids

What is the primary route of elimination of yew toxicity?

metabolism by the liver

What is the mechanism of toxicity of the yew taxus spp?

direct effects on cardiac ion channels resulting primarily in conduction distrubances