Relationships between the concentration of liver metabolites and ketogenesis in chickens fed "carbohydrate-free" diets

Rates of entry and oxidation of D(-)-3-hydroxybutyrate and glucose in fed and fasted chickens

Rates of entry and oxidation of D(-)-3-hydroxybutyrate (DBHB) and glucose and their contribution to the total metabolic production of CO2 were studied in fed and 48-hr fasted Leghorn roosters using primed constant intravenous infusions of NaH14CO3, D(-)-3-[3-14C]-hydroxybutyrate, and D-[U-14C] glucose. Fasting increased plasma DBHB concentrations sixfold but did not change plasma glucose levels. In both states of nutrition, rates of CO2 production were identical (P greater than .05). Mean fractions of the total CO2 derived from DBHB and glucose in fed and fasted chickens, respectively, were: DBHB, 1.7 and 9.9% (P less than .001); glucose, 29 and 10% (P less than .001). Entry rates of DBHB and glucose in fed chickens were 276 and 5936 mumoles/hr per kg (P less than .001), respectively, and in starved birds were 1703 and 2204 mumoles/hr per kg (P less than .001), respectively. Fasting increased the oxidation rate of DBHB from 124 to 737 mumoles/hr per kg (P less than .001) and decreased the oxidation rate of glucose from 1491 to 525 mumoles/hr per kg (P less than .001). During fasting, glucose homeostasis is maintained in part by concomitant decreases in glucose entry and oxidation rates. The results are discussed with reference to the sparing effect of DBHB on glucose oxidation.

Effect of dietary energy on hepatic glycogen metabolism in the turkey hen

An experiment was conducted with turkey hens to investigate the effect of substituting 30% of the carbohydrate calories with corn oil, 1,3-butanediol, or glycerol. Birds fed additional corn oil had the lowest liver glycogen concentration. Corn oil increased phosphorylase, a total phosphorylase, and glycogen synthetase I in comparison to the controls. Also, additional corn oil resulted in the highest specific activity of glucose-6-phosphatase. Dietary glycerol caused the highest concentration of liver glycogen. Glycerol increased glycogen synthetase I, but had little effect upon total activity in comparison to butanediol in the diet. Both butanediol and glycerol gave similar phosphorylase a activity, but butanediol increased total activity. The fat-fed and control-fed hens regulated hepatic glycogen concentration through phosphorylase, while glycerol and butanediol-fed hens regulated glycogen through glycogen synthetase. In vitro activation of glycogen synthetase I was deficient in hens fed additional corn oil, indicating a lack of glycogen synthetase phosphatase activity. The order of activation (glycerol greater than butanediol greater than control greater than corn oil) corresponds to the rank of glycogen concentrations

Studies on the growth and changes in metabolism of rats fed on carbohydrate-deficient fatty acid-based diets supplemented with graded levels of maize starch

1. Experiments were conducted to determine the effects of the supplementation of carbohydrate-deficient fatty acid-based (FA) diets with 18·7, 37·5, 75, 150 and 300 g maize starch (MS)/kg on the growth and metabolism of the growing rat. Further, the effects of fasting on rats given the FA diet were compared with those given the high-carbohydrate (CHO) diet. Due to the significant decrease in food consumption of rats given the FA diet, the effects of pair-feeding the CHO and the FA diet were also investigated.

2. The isoenergetic replacement of fatty acids with increasing amounts of MS in the FA diet given to rats increased their weight gain and concentration of glucose in their plasma. These increases, however, tended to level off for weight gain and glucose concentration, respectively, at about 18·7 g and 75 g MS/kg diet. The same type of replacement decreased the concentration of ketones in the plasma but the decrease levelled off at the high concentration of 300 g MS/kg diet. Activities of liver glucose-6-phosphatase (EC3.1.3.9) and glucokinase (EC2.7.1.2) decreased and increased respectively with increasing concentration of maize starch in the diet. These changes tended to level off at concentrations of about 75–150 g MS/kg diet.

3. Fasting for 18 h decreased the concentration of glucose in plasma of both the FA- and the CHO-fed rats, while fasting of the CHO-fed rats depressed the concentration of glycogen in the liver but did not influence that of the FA-fed rats. Pair-feeding the CHO diet to the FA diet produced similar weight increases during the 8-week experimental period.

Influence of meal-feeding on some of the effects of dietary carbohydrate deficiency in rats

1. Experiments were conducted to investigate the effects of feeding rats on a diet based on a mixture of maize oil fatty acids as the only source of non-protein energy (fatty acid diet) and the influence on these effects of giving such a diet in a single daily meal lasting 2 h.

2. In comparison with a triglyceride diet in which the non-protein energy was in the form of maize oil, feedingad lib.with the fatty acid diet produced no significant changes in body-weight gain, plasma glucose and plasma ketones concentrations, liver glycogen concentration and protein efficiency ratio.

3. In comparison with the triglyceride diet, meal-feeding with the fatty acid diet produced significantly lower body-weight gain and protein efficiency ratio; moreover, it significantly lowered plasma glucose and liver glycogen concentrations.

4. Rats meal-fed on the fatty acid diet synthesized glucose from protein, as evidenced by the significantly higher liver glycogen concentration detected 6 h after the meal had been eaten, but the increase was significantly lower than in the animals fed on the triglyceride diet. Also, 6 h after the meal had been eaten, the amount of meal remaining in the stomach of rats meal-fed on the fatty acid diet was significantly higher than in those fed on the triglyceride diet.