Nitrate and Nitrite Poisoning Flashcards
What enzyme converts Nitrate (NO3) to Nitrite (NO2)? Where does this occur?
Nitrate reductase
occurs in the plant, soil, rumen, or blood
what is Nitrite converted to?
Ammonia (NH3)
When the rate of nitrate to nitrite is reduced, with continuation of nitrate uptake from the soil, this leads to accumulation of…..
Nitrate in the plant
What plant factors will favor nitrate accumulation?
- Plant species (Sweet clover, alfalfa, wheat, corn, edible plants)
- Content and form of nitrogen in the soil (Nitrate and ammonia)
- Plant age - young and immature plants are more toxic
What soil conditions will increase nitrate uptake?
rains or moisture, acidic soil, low molybdenum, sulfur or phos, low soil temp, soil aeration and drought
T/F: Decreased light reduces activity of nitrate reductase
TRUE
What herbicides will increase the risk of ingesting nitrate accumulating plants? why?
Phenoxy acetic acid herbicides bc they increase the palatability of plants
What plant parts have the highest accumulation of nitrate?
The stalks (closest to the ground) = the most
Leaves contain less than stalks or stems The seed (grain) and flower contain little to none
T/F: More mature plants have higher concentrations of nitrates
FALSE
younger = higher nitrate
T/F: Nitrate is toxic
False
it is not toxic until it is transformed into nitrite
What plants are nitrate accumulators?
Pigweed (amaranthus retroflexus) Oats (avena sativa) Beets (beta vulgarius) Johnson grass, sudan grass, milo Corn (Zea mays) Lamb's quaters (Chenopodium album) Sweet clover (Melilotus spp) Alfalfa (medicago sativa) Wheat Sunflower (helianthus annuus)
What is sodium nitrate IV used as?
Vasodilator
horses are very sensitive
What sources are animals exposed to that they can get nitrate poisoning?
Rapid ingestion of forages or hays containing high amounts of nitrate
Accidental ingestion of feeds or water contaminated with nitrate
overdose with nitrate IV - HORSES ARE VERY SENSITIVE
T/F: Nitrates are water soluble
TRUE
Are nitrate fertilizers palatable to animals?
YES bc they’re salty
What is the toxicity of nitrate poisoning in ruminants?
Slightly toxic
500mg/kg - 1000mg/kg
T/F: Ruminants exposed to nitrate may develop a tolerance over time
TRUE
Forage greater than ___% may cause acute nitrate toxicosis in ruminants
1%
Why are ruminants the most susceptible to nitrate poisoning?
Because the conversion of nitrate to toxic nitrite occurs rapidly in the rumen due to the microflora and nitrate reductase
What animals are resistant to nitrate poisoning?
PIGS
What is the time frame of nitrate poisoning?
Can be acute OR chronic
***acute is MOST COMMON
What animals are most susceptible to nitrate poisoning?
Ruminants - more specifically young adults
3 months - 1 year of age
**prior to 3 months the rumen is not mature - so these animals are not actively converting nitrate to nitrite
What concurrent disease will increase nitrate toxicity?
Methemoglobinemia and anemia
what reaction is slower; nitrate to nitrite, or nitrite to ammonia?
Why is this important?
The rate of conversion of nitrite to ammonia is slower than nitrate to nitrite… this leads to an excess of nitrite that will be absorbed into the bloodstream
T/F: Nitrite will cross the placental barrier
TRUE
can enter fetal RBCs - they are more sensitive, then cause abortion
What is the half life of nitrate and nitrite? Why is that important?
The half life of nitrite is very short (less than 1 hour)
Nitrate half life ranges from 4-48 hours - so although it is less toxic - it is better to test for
What is the MOA of acute nitrate toxicosis?
Nitrite will react with hemoglobin –> oxidation of ferrous iron to ferric and conversion of hemoglobin to methemoglobin
Blood will be brown-yellow
What clinical signs are associated with acute nitrate toxicosis?
Signs of anemia and metheomglobinemia (30min - 4 hours)
- anoxia, vasodilation, hypotension
- patients may just die rapidly with no clinical signs
- rapid breathing, restlessness, dyspnea, weakness, ataxia, sternal recumbency, cyanosis, convulsions, death within a day for a few hours
What lesions are associated with nitrate poisoning?
Congested organs due to vasodilation
brown color of blood
What clinical signs are noted in chronic nitrate poisoning?
Abortion due to decreased progesterone
What is the specimen of choice for nitrate chemical testing if the patient died several hours ago?
Ocular fluid
greater than 30ppm indicated excessive exposure
*serum, plasma, urine, and rumen contents can be tested for nitrate but they are unstable after death
What is a good indicator of prognosis for nitrate toxicosis?
Methemoglobin concentration
animals usually die before treatment can be initiated
What is a test for nitrates in forage that can be done?
Diphenylamine test: qualitative test for nitrate in forages, rumen contents, and water
positive results indicated by 5000ppm nitrates or more
*dark blue color will indicate a positive result - positive specimens should be sent to the lab for a quantative analysis
What is the specific treatment for nitrate poisoning?
Methylene blue 1% IV slowly to tx methemoglobinemia
(different dose for cats)
Other: activated charcoal (not very effective), ruminal lavage with cold water, oral ABs (to inhibit microflora/nitrate reductase)
