Plant-Related Toxicants

Question 1

Describe the accumulation of nitrate by plants

Answer 1

• nitrate is absorbed from the soil by the plant and converted to nitrite by nitrate reductase
• nitrite is converted to ammonia
• ammonia is converted to amino acids, then to vegetable protein
• accumulation occurs with the conversion of nitrate to nitrite is reduced, but nitrate is still being taken up

Question 2

Which part of the plants/what age have the highest concentrations of nitrate?

Answer 2

• stalks contain the highest

- young plants have higher concentrations

Question 3

What are the properties of nitrate?

solubility, palatability

Answer 3

• soluble in water

- salty and palatable

Question 4

Which species are the most susceptible to nitrate poisoning?

Which are the least?

Answer 4

• ruminants are most susceptible

- pigs are resistant

Question 5

Describe the toxicokinetics of nitrate poisoining

Answer 5

• rumen microflora convert nitrate to nitrite faster than nitrite is converted to ammonia
• excess nitrite is absorbed and enters erythrocytes in exchange for Cl ions
• crosses placenta

Question 6

Describe the mechanism of action of nitrate poisoning

Answer 6

• nitrite interacts with hemoglobin: ferrous oxidized to ferric and hemoglobin converts to methemoglobin
• high mHb causes death from anoxemia
• abortions occur

Question 7

What are the clinical signs of nitrate poisoning?

Answer 7

• sudden death without signs
• rapid breathing, restlessness, weakness, ataxia, cyaosis, convulsions and death
• abortion

Question 8

What are the observed lesions in nitrate poisoning?

Answer 8

• congestion of organs

- brown colored blood

Question 9

How is nitrate poisoning treated?

Answer 9

• methylene blue 1% IV

- activated charcoal, rumen lavage, or oral antibiotics

Question 10

How are large animals usually poisoned with cyandide?

Small animals?

Answer 10

LA: ingestion of cyanogenic plants (wild cherry, sudan grass, johnson grass, and sorghums)
SA: ingestion of hydrogen cyanide and cyanide salts in many materials

Question 11

Which animals are more susceptible to cyanide poisoning?

Answer 11

• ruminants are most susceptible

- sheep less than cattle

Question 12

Describe the toxicokinetics of cyanide poisoning

Answer 12

• HCN absorbed through GI tract, inhalation, and intact skin
• distributed throughout body
• CN with thiosulfate is metabolized to thiocyanate which is less toxic and excreted in urine

Question 13

Describe the mechanism of action of acute cyanide toxicity

Answer 13

• excess cyanide in blood and tissue binds with ferric iron and copper
• blocks electron transport and inhibit cells from using oxygen
• metabolic acidosis
• decreases cellular energy
• vasoconstriction
• neuronal damage from anoxia
• irritation of mucus membranes

Question 14

Describe the mechanism of action of chronic cyanide toxicity

Answer 14

• neuronal degeneration and demyelination of spinal cord and brain
• low levels of cyanide are goitrogenic

Question 15

What are the clinical signs of acute cyanide toxicosis?

Answer 15

• rapid onset
• tachypnea, anxiety, severe panting, gasping, and behavioral alarm
• death in 4-5 minutes

Question 16

What are the clinical signs of chronic cyanide toxicosis?

Answer 16

• posterior paralysis, urinary incontinence, and cystitis
• constipation due to lower spinal cord degeneration
• possible goitrogenic effect

Question 17

What lesions are found in cyanide toxicosis?

Answer 17

• mucus membranes bright red
• blood is cherry red and may not clot
• congestion and petechiae in GI and lungs
• cyanide smell

Question 18

How is cyanide toxicosis diagnosed?

Answer 18

• elevated thiocyanate levels in urine
• lactic acidosis and increased anion gap
• sodium picrate paper test

Question 19

How is cyanide toxicosis treated?

Answer 19

• sodium nitrate 20% IV (vasodilation and methemoglobin)
• sodium thiosulfate 20% IV (converts cyanide to thiocyanate)
• sodium thiosulfate orally
• oxygen
• mineral oil, vinegar

Question 20

Which species are the most susceptible to soluble oxalate poisoning?

Answer 20

sheep and cattle

Question 21

What will reduce the toxicity of soluble oxalate?

Answer 21

• ruminants allowed to graze small quantities of oxalate containing plants
• presence of food in rumen
• calcium or calcium rich diets

Question 22

Describe the mechanism of action of soluble oxalate poisoning

Answer 22

• after absorption, oxalates combine with calcium ion to form insoluble ca oxalate
• leads to hypocalcemia and tetany, or affects bone and milk production
• precipitation of ca oxalate crystals in kidney tubules

Question 23

What are the clinical signs of soluble oxalate poisoning?

Answer 23

• colic, dullness, depression, muscle weakness and twitching, head and neck pulled to one side, prostration, coma, and death
• rapid breathing and blood-tinged froth around mouth
• fatal renal tubular toxicosis, oliguria, hyperkalemia, and cardiac failure

Question 24

What lesions are seen in soluble oxalate toxicosis?

Answer 24

• excess fluid in abdomen and thoracic cavities
• petechial hemorrhage in GI mucosa
• emphysema of lungs
• blood tinged froth in mouth and esophagus
• kidneys have dark red cortex and medullar separated by a gray line

Question 25

How is soluble oxalate toxicosis diagnosed?

Answer 25

• presence of Ca oxalate crystals in kidney tubules
• hypocalcemia
• high BUN