VPT 421: Veterinary Toxicology (2+0)

ABSORPTION AND FATE

• In the rumen, ammonia liberated is in the form of ammonium ion and hence it cannot be absorbed.
• The rate of ammonia production depends primarily on the amount of ration ingested, amount of urease in the ruminal contents or the diet and pH of the ruminal contents.
• At rumen pH 6.2 major fraction of the N2 released exists as NH4+ ions. This charged ion is highly water soluble and poorly absorbed.

• At pH 9, NH3/NH4+ reaches to one (pKa of ammonium ion is 9.3) and large amount of ammonia is available for absorption.
• If rumen pH is elevated to 10 or above, then ammonia will be in soluble form and lacks charge and can be absorbed.

• In the blood at a pH of 7.4, almost all the ammonia is in the form of ions and cannot cross the cell membrane.
• In the normal course, liver ammonia is converted into urea by the urea cycle or incorporated into glutamic acid in the synthesis of glutamine.
• Both these detoxification processes are enzymatic and depend on substrates produced by citric acid cycle.