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Studies were conducted to examine the relationship between changes in liver xanthine dehydrogenase with those in uric acid excretion during a 10-day adaptation period in chicks fed diets containing 25 or 75% isolated soybean protein. Food consumption, weight gain and liver nitrogen were also determined. Marked reductions in food consumption and weight gain were noted the first 24 hours in chicks fed the high protein diet as compared with chicks fed a control diet containing 25% isolated soybean protein. Consumption of the high protein diet and weight gain increased markedly after the initial 24 hours and remained at approximately 80% of the levels observed for control chicks throughout the remainder of the experiment. Liver weight, expressed on a body weight basis, was significantly increased in chicks fed the high protein diet for the first 2 days, after which time the differences between the 2 treatment groups largely disappeared. Elevated liver nitrogen levels were observed throughout the experiment for birds fed the high protein diet. Liver xanthine dehydrogenase activity increased twofold in chicks fed the high protein diet for 1 day and reached a maximum fourfold increase by day 4. A direct relationship between the elevated activity of hepatic xanthine dehydrogenase measured in vitro and the uric acid excretion was observed in these studies.

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.

Studies were conducted to investigate growth, mortality, feed consumption, plasma and femur magnesium levels, hemoconcentration, and magnesium balance in chicks fed diets deficient or marginally adequate in magnesium and differing in the source of carbohydrate. Four carbohydrate sources, glucose, sucrose, lactose and starch, and 4 levels of magnesium, 250, 300, 350 and 400 ppm, were fed in one or more of the studies. The results of these studies indicated that chicks fed diets containing lactose exhibited decreased mortality, increased feed and water consumption, higher plasma and femur magnesium levels, and higher hematocrit values than did chicks fed similar diets differing only in carbohydrate source. Weights of chicks fed diets containing lactose and 250 or 300 ppm of magnesium were slightly higher during the first 2 weeks of the experiment as compared with chicks fed diets containing different carbohydrate sources. Similar results were not observed for these chicks at 3 or 4 weeks of age nor for chicks fed 350 or 400 ppm of magnesium at any age, however. A final study measured magnesium balance in chicks fed either a glucose diet ad libitum, a lactose diet pair-fed to the glucose diet, or a lactose diet ad libitum. These studies suggested that one means by which lactose exerts a beneficial effect in diets marginal in magnesium content is through increased feed, and hence, increased magnesium consumption. Hemoconcentration may also be a factor partially responsible for the increased plasma magnesium levels of chicks fed the lactose diets.

The utilization of orally or intraperitoneally administered 28Mg was studied in chicks fed diets containing 300 ppm magnesium and either glucose or lactose (25% of diet) plus glucose as carbohydrate sources. No significant influence of the dietary carbohydrate was observed on the retention of orally or intraperitoneally administered 28Mg in the whole chick. Radioactivity in the blood at the initial withdrawal and in the femur at the termination of the experiments, however, indicated an increased concentration of 28Mg in these tissues for chicks fed lactose in their diets. These differences were statistically significant only for chicks receiving the isotope by oral administration. The radioactivity in the blood and femur of chicks given intraperitoneal injections of 28Mg was not significantly altered by the source of carbohydrate, although these values were higher for birds fed lactose in their diets. Lactose, in addition to its influence on increased feed consumption and hemoconcentration which were previously reported, appears also to exert a stimulatory influence on magnesium absorption in the chick.

The recent development of sensitive radiochemical assays has facilitated the detection of glycerokinase activity in adipose tissue. However, the effects of dietary manipulation on the activity of this enzyme in adipose tissue have not been investigated. Experiments were conducted to:1)detect and characterize glycerokinase activity in the chicken;2)compare relative changes in glycerokinase activity in lean and obese laying hens, and3)examine the physiological effects of dietary manipulation on glycerokinase activity in the laying hen and growing chicken.Adipose tissue glycerokinase activity was detected in the chicken by a radiochemical assay which appeared sensitive enough to measure nanomoles per hour (units) of enzyme activity. Obese laying hens appeared to have higher glycerokinase activity than lean hens but this difference was not statistically significant. Fasting and refeeding laying hens produced significant changes in enzyme activity and plasma glycerol concentration, but plasma glucose was not affected. Feeding a high fat (carbohydrate-free) diet to growing cockerels significantly increased plasma glycerol and appeared to increase glycerokinase activity above the control diet (high carbohydrate). Glycerokinase activity was not correlated with plasma glycerol but was significantly correlated with abdominal fat pad weight of the cockerels. These results indicate that the physiological importance of glycerokinase in chicken adipose tissue appears to be positively correlated with the degree of obesity.

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.