Lead Flashcards
T/F: Lead is not readily degraded in the environment
TRUE
it is persistent
T/F: Lead is readily absorbed and metabolized
False
only about 1-2% if absorbed from the GIT because it forms insoluble compounds
What pH conditions favor lead dissolution?
Acidic
What sources of lead are pets exposed to?
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
What is more readily absorbed, organic lead or inorganic lead?
Organic lead bc it is lipid soluble
Can be absorbed by the skin and accumulated in fat
What is organic lead used for?
Anti-knocking agents in gasoline products
Where is inorganic lead found?
in dyes, paints, and pesticides
Poor absorption due to low water solubility
What is the lowest lethal dose of lead in dogs?
191 mg/kg
What animals are most vulnerable to lead toxicosis related deaths?
Waterfowl
ingest spent pellets or lost fishing sinckers
Birds shot with lead pellets can become a source of secondary poisoning for other animals
What two ions will lead displace in the blood?
Ca and zinc
What dogs are most sensitive to lead poisoning?
Puppies are more sensitive than adults due to the permeability of the BB
What are the routes of lead absorption?
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
What molecules will decrease the absorption of lead in the GIT?
Calcium, zinc, and protein
Lead is absorbed by active transport using the same carrier protein as calcium
If a patient is deficient in ____, then lead is more readily absorbed
Vitamin D
Calcium
Zinc
Iron
In what animals is GIT absorption of lead greatest?
Immature animals
up to 50% compared to 5-15% in adults
Does lead cross the BBB or placental barrier?
YES
crosses BBB in young animals
What does lead bind to for transport in systemic circulation?
Binds to erythrocyte membrane (60-90% RBC binding depending on species)
Lead can stay in the soft tissue for ____ weeks
4-6
Where can lead be stored in the body for years?
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
What chelating liver protein involved in cellular detoxification of inorganics, will sequester lead when it is in high concentrations?
Metallothionein
Where is lead excreted?
Primarily through the urine
Bile and milk as well
What are the target tissues of lead toxicosis?
GIT, blood, CNS
What is the MOA of lead toxicosis?
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
What is the MOA in chronic lead toxicosis?
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
What GIT signs are associated with lead toxicosis?
Oral exposure:
anorexia, salivation, vomiting, “lead colic”, dhr or constipation
*rare - megaesophagus
What are the hematological clinical signs associated with lead toxicosis?
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
What CNS signs are associated with lead toxicosis?
CNS inhibition of neurotransmitters = CNS hyperexcitability OR CNS depression
*depends on which neutrotransmitters are spontaneously released OR blocked
Dopamine, Ach, GABA
What lesions are associated with lead toxicosis?
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
What abnormalities may be present in the UA of an animal with lead toxicosis?
Porphyria: due to lead inhibition of porphobilinogen synthase
hemoglobinuria - increased heme
What kind of anemia is associated with lead toxicosis?
Can be regenerative or non regenerative (poor bone marrow response)
What radiographic changes can be noted in an animal with lead poisoning?
Metaphyseal sclerosis in young animals with chronic lead toxicosis
“lead line”
T/F: Lead lines represent lead deposits in the bone
FALSE
sclerosis of the metaphysis
Lead inhibits normal remodeling of the long bones
What is the antemortem specimen of choice for lead toxicosis? What value is diagnostic?
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)
T/F: Lead toxicosis should always bc a ddx when a dog or cat presents with unexplained GI signs and abdominal pain
TRUE
Is activated charcoal recommended for lead ingestion?
NO
does not bind well to heavy metals
What tx is available for lead toxicosis?
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
What potential side effects are associated with chelation therapy for the tx of lead toxicosis?
Can result in hypocalcemia and kidney damage
What chelating agents are used for tx of lead toxicosis?
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
What is the prognosis for lead toxicosis?
Good in animals with mild to moderate signs that are treated promptly and appropriately
Guarded to poor if animals are showing severe CNS signs
