BIOCHEMICAL STUDIES ON THE EFFECT OF ZINC ON THE LIVER FUNCTIONS AND IMMUNOLOGICAL STATUS IN CHICKENS

Abstract

The role of zinc as an essential trace element was first described by Todd et aL (1934)who foud that Zinc is an indispensable dietary constituent for normal growth and survival in rats. Also, it was first shown to be required for the growth of the mold Aspergillus Niger (Raulin, 1869). Since then, zinc has been demonstrated to be essential for the growth, development and differentiation of all types of life, including microorganisms, plants and animals (Vallee, 1986). It is well recognized that an increase in Zn status of an·animal results in increased synthesis of metallothionein (MT) in many different tissues (Richards, 1989). Many nutritional factors influence the immune system functions is now well known. The abnormal incidence of various infections and the existence of lymphopenia and lymphoid organ atrophy in malnourished cases have been repeatedly demonstrated, and evidence points to zinc_ insufficiency as a link to this type of immunodeficiency. It is now widely recognized that zinc is one of the essential trace elements and a member of one of the major micronutrient subgr ups in human and animal nutrition (Rink andGabri(!l, 2000; Auld, 2001).

After iron, zinc is the second most abundant trace metal in the human body; an average 70-kg adult human contains 2.3 g of zinc (Mc-Cance and Widdowson 1942). Keilin and Mann, (1940) isolated and purified the enzyme, carbonic . anhydrase, and showed that it is a metalloenzyme containing 0.33% zinc as a part of the molecule. This enzyme catalyzes the breakdown of carbonic acid to C02 and H20. Several enzymes in the animal body are known to contain zinc; these include carbonic anhydrase, glutamic dehydrogenase, lactate dehydrogenase, alkaline phosphatase and a number of pyridine nucleotide dehydrogenases. In addition zinc acts as a co-factor for many enzymes, necessary for DNA synthesis (Hoekstra, et al., 1974 and Mc-Donald, et al., 1979). Approximately, 300 zinc enzymes covering all six classes of enzymes and in different species of all phyla have been discovered (Vallee and Auld 1990, Christianson 1991, Coleman