Dietary-induced Depletion and Repletion of Avian Liver Xanthine Dehydrogenase

Abstract

Changes in body weight, liver weight, liver nitrogen, liver xanthine dehydrogenase (XDH) and plasma uric acid levels were studied in chicks previously fed a diet containing 25% (control) or 75% isolated soybean protein, and subsequently starved or fed a protein-free diet from 1 to 4 days. The influence of realimentation of the two diets following periods of starvation or the feeding of the protein-free diet was also studied. A close relationship between the increases in XDH activity and plasma uric acid was observed during adaptation of chicks to the high protein diet. A 70% increase in total liver XDH activity was observed 12 hours after the initiation of the high protein diet. The increase in liver XDH activity was essentially linear the first 2 days, at which time a maximal response to the high level of dietary protein was observed. Body weight, liver weight and liver nitrogen decreased in control chicks from the beginning of the fasting period, whereas liver XDH activity did not begin to decrease until after 24 hours. Plasma uric acid levels gradually increased throughout the fasting period. These results were in contrast to the concomitant depressions in liver XDH activity and plasma uric acid observed during the first 24 hours of the fast in chicks adapted to the high protein diet. Both groups of chicks exhibited increased liver weights, and decreased liver nitrogen, XDH activity and plasma uric acid following the consumption of the protein-free diet from 1 to 4 days. A larger increase in XDH activity was noted in chicks fed the protein-free diet than in fasted chicks following the realimentation of the high protein diet, whereas the increases were of a similar magnitude when the control diet was refed. The different metabolic influences exerted by the consumption of a protein-free diet and by starvation on the parameters studied are discussed.