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; serine0threonine protein phosphatase

How does cantharidin cause toxicity?

blocks adenosine A1 receptors, which regulate 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 is the toxic principle of foxglove digitalis spp?

digitalis glycosides

What parts of the foxglove digitalis contain the toxic compound?

all parts

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?

inhibition of Na-K pump

What are the toxic principles in milkweed asclepias spp?

cardenolides and galitoxin

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

foxglove

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

cardiac glycosides; oleandrin and neriine

True or false: Oleancer toxins are detected in milk.

true

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

convallotoxin (cardiac glycoside)

What is the toxic principle of the azalea rhododendron spp?

grayanotoxin

What is the mechanism of toxicity for azaleas?

bind to voltage gated sodium channels producing depolarization

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 is the toxic principle of avocado persea americana?

persin

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

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? What does it cause?

gossypol; myocardial necrosis

True or false: All parts of the yew taxus spp are toxic except the aril encapsulating the seed.

true

What is the toxic principle in the yew taxus spp?

taxine alkaloids

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

direct effects on cardiac ion channels