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Toxicology Fall17 > Lead > Flashcards

Lead Flashcards

1
Q

T/F: Lead is not readily degraded in the environment

A

TRUE

it is persistent

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2
Q

T/F: Lead is readily absorbed and metabolized

A

False

only about 1-2% if absorbed from the GIT because it forms insoluble compounds

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3
Q

What pH conditions favor lead dissolution?

A

Acidic

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4
Q

What sources of lead are pets exposed to?

A

Most common source is lead based paints

A thumbnail sized chip of paint could have 50 - 200 ppm lead in it

other: batteries, putty, galvanized wire, lead shots, linoleum

**areial emission from combustion of leaded fuel, insecticides/herbicides

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5
Q

What is more readily absorbed, organic lead or inorganic lead?

A

Organic lead bc it is lipid soluble

Can be absorbed by the skin and accumulated in fat

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6
Q

What is organic lead used for?

A

Anti-knocking agents in gasoline products

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7
Q

Where is inorganic lead found?

A

in dyes, paints, and pesticides

Poor absorption due to low water solubility

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8
Q

What is the lowest lethal dose of lead in dogs?

A

191 mg/kg

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9
Q

What animals are most vulnerable to lead toxicosis related deaths?

A

Waterfowl
ingest spent pellets or lost fishing sinckers

Birds shot with lead pellets can become a source of secondary poisoning for other animals

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10
Q

What two ions will lead displace in the blood?

A

Ca and zinc

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11
Q

What dogs are most sensitive to lead poisoning?

A

Puppies are more sensitive than adults due to the permeability of the BB

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12
Q

What are the routes of lead absorption?

A

Dermal - organic based is absorbed better this way than inorganic

Inhalation and absorption via lungs - arial spraying of lead based pesticides (not in US)

**Ingestion* - oral absorption is poor, but increased absorption in GIT due to acidic pH

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13
Q

What molecules will decrease the absorption of lead in the GIT?

A

Calcium, zinc, and protein

Lead is absorbed by active transport using the same carrier protein as calcium

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14
Q

If a patient is deficient in ____, then lead is more readily absorbed

A

Vitamin D
Calcium
Zinc
Iron

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15
Q

In what animals is GIT absorption of lead greatest?

A

Immature animals

up to 50% compared to 5-15% in adults

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16
Q

Does lead cross the BBB or placental barrier?

A

YES

crosses BBB in young animals

17
Q

What does lead bind to for transport in systemic circulation?

A

Binds to erythrocyte membrane (60-90% RBC binding depending on species)

18
Q

Lead can stay in the soft tissue for ____ weeks

A

4-6

19
Q

Where can lead be stored in the body for years?

A

In the active bone matrix compete with Ca

larger amounts in young (83-95%) vs old (70-75%)

Biologically inactive in the bone but can be released back into systemic circulation due to fracture etc

20
Q

What chelating liver protein involved in cellular detoxification of inorganics, will sequester lead when it is in high concentrations?

A

Metallothionein

21
Q

Where is lead excreted?

A

Primarily through the urine

Bile and milk as well

22
Q

What are the target tissues of lead toxicosis?

A

GIT, blood, CNS

23
Q

What is the MOA of lead toxicosis?

A

Interferes with biological structure and function

Can substitute for Ca, Zn, Mg, Fe

Competes with Ca in the bone and alters Ca movement across membranes –> Alters structure of the cerebral endothelium - edema

24
Q

What is the MOA in chronic lead toxicosis?

A

Chronic low exposures - inhibites heme synthesis that leads to anemia (also decreased RBC lifespan)

inhibits regulation of Ca

Alters release of neurotransmitters (dopamine, acetylcholine, GABA)

**breakdown of BB via injury to endothelial cells and alteration of the microvascular systems

25
Q

What GIT signs are associated with lead toxicosis?

A

Oral exposure:
anorexia, salivation, vomiting, “lead colic”, dhr or constipation

*rare - megaesophagus

26
Q

What are the hematological clinical signs associated with lead toxicosis?

A

Clinical signs related to anemia
Basophilic stippling of erythrocytes

Antemortem: Whole blood concentration >0.35 ppm = lead toxicosis

Postmortem: Liver and kidney >10ppm = lead toxicosis

27
Q

What CNS signs are associated with lead toxicosis?

A

CNS inhibition of neurotransmitters = CNS hyperexcitability OR CNS depression

*depends on which neutrotransmitters are spontaneously released OR blocked

Dopamine, Ach, GABA

28
Q

What lesions are associated with lead toxicosis?

A

non specifc, may find lead objects in the GIT

Histo: cerebral cortical necrosis and poliomalacia in cattle
*acid fast eosinophilic intranuclear inclusion bodies in renal tubular epithelium or hepaticytes

29
Q

What abnormalities may be present in the UA of an animal with lead toxicosis?

A

Porphyria: due to lead inhibition of porphobilinogen synthase

hemoglobinuria - increased heme

30
Q

What kind of anemia is associated with lead toxicosis?

A

Can be regenerative or non regenerative (poor bone marrow response)

31
Q

What radiographic changes can be noted in an animal with lead poisoning?

A

Metaphyseal sclerosis in young animals with chronic lead toxicosis

“lead line”

32
Q

T/F: Lead lines represent lead deposits in the bone

A

FALSE

sclerosis of the metaphysis

Lead inhibits normal remodeling of the long bones

33
Q

What is the antemortem specimen of choice for lead toxicosis? What value is diagnostic?

A

Whole blood
>90% of circulating lead is bound to RBCs

Blood lead > 0.4ppm with clinical signs = diagnostic or > 0.6ppm without clinical signs

(PM - test liver, kidney, GIT)

34
Q

T/F: Lead toxicosis should always bc a ddx when a dog or cat presents with unexplained GI signs and abdominal pain

A

TRUE

35
Q

Is activated charcoal recommended for lead ingestion?

A

NO

does not bind well to heavy metals

36
Q

What tx is available for lead toxicosis?

A

Stabilize and supportive care first.

Eliminate Pb: wash haircoat, cathartics, gastric lavage

Chelation therapy: use of chelating agents to detoxify - by forming multiple bonds with metal ions rendering them inactive and ready for excretion

37
Q

What potential side effects are associated with chelation therapy for the tx of lead toxicosis?

A

Can result in hypocalcemia and kidney damage

38
Q

What chelating agents are used for tx of lead toxicosis?

A

Calcium disodium EDTA - most commonly used - primary concern is renal injury

  • binds to other minerals so concurrent supplementation is recommended
  • until it is all chelated, mobilized Pb in the circulation can redistribute in order to achieve equilibrium - re-toxification
39
Q

What is the prognosis for lead toxicosis?

A

Good in animals with mild to moderate signs that are treated promptly and appropriately

Guarded to poor if animals are showing severe CNS signs

Toxicology Fall17 (38 decks)

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