Ontogenetic study of enteric xanthine oxidase in the chick embryos: focus on the late embryogenesis

Xanthine oxidase (XO) is a member of xanthine oxidoreductase (XOR) enzyme system that catalyses the terminal reactions of purine degradation to uric acid (UA). The synthesis of both antioxidant (i.e. UA) and numerous free radicals makes XO an important regulator of the cellular redox potential involved in normal foetal development. The aim of this study was to investigate ontogenetic changes of enteric XO activity and UA content during the last week of chick embryonic development. Fertilized eggs ( n = 180) of layer-breeder (Bovans White) and broiler-breeder hens (Ross 308) were incubated at 37.7 °C and 60 % relative humidity. Enteric XO activity ( n = 10 for each strain) was spectrophotometrically measured, based on the generation of UA using xanthine as substrate, at various incubation days namely D14, D16, D18, D20 and D21. Intestinal XO activity and UA content of both strains fluctuated and showed polynomial relationships with embryo age. The XO activity tended to be increased from D14 and reached its maximum level around D18 in both strains; however, its activity returned to minimal values at D21. Intestinal XO activity in broiler embryos was higher when compared to that of layer embryos at D18. The pattern of change in levels of intestinal UA were similar for the two strains with the highest UA levels being detected at D21. We have shown that the intestinal XO activity and UA content of chick embryos fluctuates during the last week of embryonic development.