VPT 421: Veterinary Toxicology (2+0)

MECHANISM OF TOXICITY

• Nitrite is the actual toxic compounds.
• Ruminants are more susceptible to nitrates than monogastric animals.
• Rumen microorganisms reduce nitrate ion to nitrite ion.
• Nitrites induce toxicity by two mechanisms.
• In the first mechanism, circulatory haemoglobin is converted to methaemoglobin.
• One mole of absorbed nitrite reacts excessively with two moles of haemoglobin and in this process there is loss of an electron and ferrous form of iron in haemoglobin is converted to ferric form resulting in methaemoglobin formation.

• When 20% of haemoglobin is converted to methaemoglobin, toxic symptoms are noticed.
• When 80% of haemoglobin is converted, anoxia and clinical signs are noticed and death occurs.
• Relaxation of vascular smooth muscle and consequent vasoldilatation are considered to be the other mechanisms of toxicity.
• The vasodilatation due to nitrites results in systemic arterial hypotension and decreased cardiac output.
• Nitrates have a direct caustic effect on the lining of the gut, if consumed in large quantities.