Effect of Alterations in Protein Intake on Liver Xanthine Dehydrogenase in the Chick

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Studies were conducted to investigate the influence of alterations in protein intake on body weight, liver weight, liver nitrogen and liver xanthine dehydrogenase (XDH) activity of chicks. After a 10-day period in which all chicks were fed a diet containing 25% isolated soybean protein, one-half of the chicks were changed to a diet containing 75% isolated soybean protein and one-half were continued with the 25% diet. The results of these studies showed no significant difference in body or liver weights at 20 days between birds fed the 25 and 75% isolated soybean protein diets. Fasting for 24 hours resulted in a similar decrease in body and liver weights for birds fed the two protein levels, but the decrease in liver N was greater for birds fed the high protein diet. Feeding a protein-free diet for 24 hours resulted in larger livers and lower total liver N as compared with control values. Regardless of the basis for expressing enzyme activity, liver XDH was significantly higher for birds fed the high protein diet ad libitum as compared with birds fed the 25% isolated soybean protein diet. Liver XDH levels of chicks that had been fed the high protein diet ad libitum and subsequently fed a diet devoid of protein, or fasted, for 24 hours were also significantly higher than those observed in chicks from similar treatments previously fed the 25% isolated soybean protein diet. In most cases, a 24-hour starvation period did not significantly lower total liver XDH as compared with ad libitum controls at each protein level, whereas feeding a protein-free diet for 24 hours resulted in significantly lower liver XDH levels.