Influence of Dietary Carbohydrate,Fat, and Protein on Lipogenesis in Rats

The incorporation of ¹⁴C of acetate-1-¹⁴C into the lipids of the liver and carcass, and the changes in the concentrations of nucleotides and citric acid in the liver were studied in the rats fed individual nutrients; starch, casein or corn oil. And the metabolism of citric acid-1,5-¹⁴C was also investigated after the feeding of nutrients. Lipogenesis in the liver and carcass was more markedly stimulated with starch than with casein or corn oil. In the liver of rats fed starch, the concentration of ATP doubled and that of citric acid was one-half of those with casein or corn oil, respectively. And the conversion of citric acid to carbon dioxide and lipids was stimulated with starch.     

Glycine-U-14C Metabolism in Young Rats Fed the 10% Casein Diets Containing Excess Glycine

Nine hours after rats fed ad libitum for 14 days a 10% caein diet (10C), a 10% casein diet containing 7% glycine (10C7G) and a 10% casein diet containing 7% glycine with 1.4% l-arginine HCI and 0.9% l-methionine (10C7GArgMet) were force-fed 10 ml of each diet suspension containing 5 μCi of glycine-U-¹⁴C per 100 g of body weight, the radioactivity recoveries of ¹⁴C in expired CO₂, tissue components and urine were determined.

The radioactivity recovery of ¹⁴C in the expired C0₂ of the 10C7G group was generally higher than that of the 10C7GArgMet group, and those of both groups would have been much higher than that of the 10C group unless the isotope had been diluted. The amount of expiratory ¹⁴C of rats fed a 25 % casein diet containing 7% glycine was not different from that of the 10C7G group. The recovery of ¹⁴C in the trichloroacetic acid (TCA) soluble fraction of muscle of the 10C7G and the 10C7GArgMet groups were greater than that of the 10C group, but there was no difference between the 10C7G and the 10C7GArgMet groups. The recoveries of ¹⁴C in the TCA soluble fraction and protein of plasma and liver, and the muscle protein were negligible in all the groups. The amount of glycine-¹⁴C incorporated into the carcass lipids of the 10C7GArgMet group was larger than that of other groups. Those in the carcass lipids of the 10C7G and the 10C7GArgMet groups would have been much higher than that of the 10C group unless the dilution of the isotope had taken place. The recoveries of ¹⁴C in the liver and muscle glycogen, and liver lipids were remarkably small in all the groups. From the above results, it was suggested that the degradation of glycine-¹⁴C to expiratory CO₂ was not accelerated, but the rate of incorporation of the isotope into carcass lipids was increased by the supplementation of l-arginine and l-methionine to the 10C7G diet as compared with that of rats fed the 10C7G diet.     

Effects of Different Ratios of Mixture of Starch and Casein,or Starch and Fat,in Diets on Lipogenesis in Rats

Studies were made on the incorporation of ¹⁴C of acetate-1-¹⁴C into the lipids of the liver and carcass, and changes in the concentrations of nucleotides, citric acid, and free fatty acids in the liver, using rats fed diets consisting of starch and casein, or starch and corn oil, at different ratios. Lipogenesis was stimulated with an increase in the content of starch both in the starch-casein and starch-corn oil diets. There was a rapid drop in lipogenesis in rats fed the diet with a little increment in the content of corn oil. Lipogenesis decreased gradually with an increment in the content of casein in the starch-casein diet. A positive correlation was found between lipogenesis and the level of ATP in the liver. The concentration of citric acid decreased with an increase in lipogenesis in the liver. Changes in dietary composition did not produce any significant alteration in the concentration of free fatty acids in the liver.     

Lipogenesis in Fatty Liver by Amino Acid Imbalance

Lipogenesis in the fatty liver of rat which was induced by feeding an amino acid-irnbalanced diet containing 8% casein supplemented with 0.3% dl-methionine has been investigated by measuring the incorporation of acetate-1-¹⁴C into various lipid fractions during in vitro incubation of liver slices.

In the incorporation of acetate-1-¹⁴C into the total lipid per one g of the slices, no significant difference for the imbalance group was observed. However, the total radioactivity of liver lipid per 100 g of the body and the incorporation into triglyceride in the lipids were significantly higher in the imbalance group than in the control group. Conversion of acetate-1-¹⁴C to CO₂ was not impaired in the imbalance group.

It is evident from these results that the induction of this type of fatty liver is due mainly to the synthesis of triglyceride.     

Effect of Glutathione on Lipogenesis in Liver Slices from Rats Fed on Low Casein Diet

To study the mechanism of fatty infiltration in the liver due to added sulfur-containing amino acids to low casein diet, the effect of sulfur-containing amino acids and glutathione (GSH) on the incorporation of acetate-l-¹⁴C into lipid fractions were studied in liver slices from rats fed on 8% casein diet (Basal diet) with or without added methionine (Met).

The liver acetyl Co A carboxylase activities of rats on basal diet with or without added Met were similar.

Addition of Met, cystine or cysteine to the incubation medium had little effect on lipogenesis of slices. On addition of GSH to liver slices from rats fed on basal diet, lipid formation increased appreciably. On the other hand, addition of GSH to liver slices from rats fed on Met supplemented diet showed no accelerative effect on lipogenesis.

Addition of GSH to the incubation medium of liver slices from rats fed on basal diet tended to reduce the incorporation of acetate into the phospholipid fraction and to increase into the fatty acid fraction of liver slices.

The content of liver GSH was lower in rats on basal diet than in those on Met supplemented diet. The higher GSH level in rats on Met supplemented diet may be one factor causing fatty infiltration in the liver of these animals.     

Monotertiarybutylhydroquinone effects on Tetrahymena pyriformis.

The molecular toxicity of monotertiarybutylhydroquionone (TBHQ) was studied using $\text{Tetrahymena}$$\text{pyriformis}$ as a model cell system. TBHQ at 26 ppm in the media inhibited cell growth by 50%. TBHQ inhibited the oxidation of ¹⁴C-acetate to ¹⁴CO₂. In addition, increasing concentrations of TBHQ decreased the incorporation of ¹⁴C-acetate into lipids and protein, ¹⁴C-amino acids into protein, ³H-uridine into RNA and ³H-thymidine into DNA. The incorporation of ¹⁴C-acetate into glycogen increased with concentrations up to 20 ppm TBHQ in the media while glycogen synthesis decreased with 40 ppm TBHQ.     

Effect of Retinol on Liver Lipid Metabolism of Rats

Effect of feeding 4.23, 16.94 and 27.53 mg of retinol daily for 10 days on the liver lipids of adult rats has been studied. Feeding of different amounts of retinol produced dose dependent toxicity symptoms in rats. Retinol feeding resulted in significant elevations of liver total lipids, total fatty acids, and glycerides, The amounts of liver esterified cholesterol were significantly raised in rats fed different amounts of retinol. Acetate-1-¹⁴C incorporation was increased in liver total cholesterol of rats fed 27.53 mg retinol and in free cholesterol of all retinol fed rats. Total ¹⁴C activity of hepatic triglycerides of retinol fed rats was the same as that of control, but their specific activity was decreased. Significant alterations were noted in phosphatidyl serine, lysophosphatidyl choline, lysophosphatidyl ethanolamine, sphingomyelin, phosphatidyl choline, phosphatidyl ethanolamine and phosphatidic acid and polyglycerophosphate fractions in liver rats fed different amounts of retinol.     

Differences in portal flow rates of amino acids and liver composition between rats fed casein or lactalbumin

The portal appearance rates and net rates of amino acids' absorption were studied in rats fed semi-synthetic diets containing either casein or lactalbumin (CAS and LA, respectively) as the only protein sources. Rats were pre-adapted to the experimental diets for 5 days prior to the absorption studies. Rats fed the LA diet had higher (p < 0.05) portal vein concentrations of free essential amino acids than those fed the CAS diet at 0, 60, 105 and 150 min after feeding. Portal and arterial concentrations of arginine, leucine, tryptophan, lysine and methionine were higher (p < 0.05) in rats fed LA at most time points tested, while concentrations of tyrosine were higher (p < 0.05) in CAS fed rats. When portal flow rates were compared, values for arginine, threonine, alanine, leucine, tryptophan and lysine were higher (p < 0.05) in LA at most time points tested, while proline, tyrosine and valine were higher (p < 0.05) for CAS fed rats after 60 and 105 min feeding. Portal blood flow varied (p < 0.05) with time in rats fed protein-free or LA diets, and was higher (p < 0.05) than that of CAS at 105 min. Intestinal net rates of absorption of tyrosine, valine, leucine and lysine were higher (p < 0.05) for LA fed rats as compared to those fed CAS at most time points tested, while alanine and proline net rates were higher (p < 0.05) for CAS fed rats at 60, 105 and 150 min. Amounts of protein in stomach contents of rats fed the CAS diet were significantly higher (p < 0.05) than those in LA fed rats at 60, 105 and 150 min after feeding. The relative liver weight of the rats fed the CAS diet was lower (p < 0.05) than that of animals fed the LA diet. Lower (p < 0.05) liver glycogen and lipid contents were determined in rats fed CAS diet respect to LA or protein-free fed rats. Results indicate that dietary and plasma amino acids profile are only partially related, and that under normal feeding conditions amino acids from CAS and LA are absorbed at different rates, which is likely to affect liver composition and metabolism.     

Hepatic Subcellular Fractions Lipids in Rats Fed Millet (Sorghum vulgarie) at Different Protein Levels

Effect of feeding defatted millet (Sorghum vulgarie) flour at 5, 10 and 14.5% protein levels respectively for six weeks has been studied on rat liver mitochondrial, microsomal and supernatant fractions total lipids, cholesterol, triglycerides, total phospholipids, phosphatidyl choline and phosphatidyl ethanolamine. The results have been compared with rats fed casein at 10% level for the same period. The metabolism of liver subcellular fractions lipids of millet diet and casein diet fed rats has been studied by the incorporation of acetate-1-¹⁴C and . A significant increase in mitochondrial triglycerides of rats fed millet diet at 5 and 10% protein level, in microsomes of rats fed millet diet at 5, 10 and 15% protein levels and in supernatant fractions of rats fed millet diet at 5 and 15% protein levels was observed. A significant increase in total cholesterol in mitochondria and microsomes and a significant decrease in supernatant fraction of rats fed millet diet at 10% protein level was observed. A significant increase in mitochondrial total phospholipids, phosphatidyl choline and phosphatidyl ethanolamine in rats fed millet diet at 10% protein level and a decrease in these in rats fed millet diet at 5 per cent protein level was observed. In microsomes total phospholipids were increased in rats millet diet at 10% protein level and phosphatidyl choline was increased in rats fed millet diet at 15% protein level. Total phospholipids, phosphatidyl choline and phosphatidyl ethanolamine were significantly reduced in the supernatant fraction of rats fed millet at 10% protein level.

Incorporation of acetate-1-¹⁴C into nonsaponifiable fraction of mitochondria, microsomes and supernatant fractions of rats fed millet diet at 5 and 15 % protein levels was significantly greater, and in saponifiable fractions of the above subcellular fractions was greater in rats fed millet diet at 5 per cent protein level. The specific activity (counts/min/mg) of free cholesterol in mitochondria, microsomes and supernatant fractions of millet diet fed rats was significantly greater, whereas the specific activity of triglycerides was not significantly different from the controls. The acetate-1-¹⁴C specific activity of phosphatidyl choline and phosphatidyl ethanolamine was significantly greater in all the above subcellular fractions of millet diet fed rats (except of phosphatidyl choline in rats fed millet diet at 5 % protein level). The specific activities of phosphatidyl choline were significantly greater in mitochondria of rats fed millet diet at 5 % protein level and of phosphatidyl choline and phosphatidyl ethanolamine in microsomes and supernatant fractions of rats fed millet diet at 5 and 15% protein levels. The specific activities of phosphatidyl choline were significantly decreased in mitochondria and microsomes of rats fed millet diet at 10% protein level. The total acetate-1-¹⁴C activities (counts/min/g equivalent wet liver) of free and esterified cholesterol triglycerides, phosphatidyl choline and phosphatidyl ethanolamine showed that their synthesis from acetate-1-¹⁴C was either enhanced in millet diet fed rats or was comparable to the controls. The total activity of (counts/min/g equivalent wet liver) into phosphatidyl choline and phosphatidyl ethanolamine showed that their synthesis was decreased in microsomes of rats fed millet diet at 10% protein level, increased in rats fed millet diet at 5 and 15% protein levels.     

Synthesis of Terpene Alcohol Esters by Lipase

The metabolic fates of the carbon skeletons of L-(U-¹⁴C)arginine, proline and glutamic acid were investigated in growing rats fed with diets containing different percentages of protein calories (0, 5, 10, 15 and 30 PC%) at 4100 kcal of metabolizable energy per kg of diet.

The incorporation of ¹⁴C into body protein at 12hr after the injection of ¹⁴C-arginine was more than 50% of the dose in all dietary groups, showing a high efficiency of utilization of this amino acid for protein synthesis. The incorporation of ¹⁴C into body protein from ¹⁴C-proline was most increased in the 15 PC% group, and the values were reduced in rats fed with lower and higher PC% diets. The carbon skeleton of ¹⁴C-glutamic acid was extensively oxidized to expired carbon dioxide, and the ¹⁴C incorporation into body protein was markedly less. The pattern of expired ¹⁴C0₂ production from each ¹⁴C-amino acid was in inverse proportion to that of ¹⁴C incorporation into body protein. The results indicate that the metabolic responses of arginine, proline and glutamic acid to dietary protein change at 10 to 15 PC%, where the growth rate reached its approximate maximum.     

Metabolic Effects of Arginine and Methionine Supplement on Rats Fed Excess Glycine Diets

The contents of glycogen, lipid, urea and amino acids, and some enzyme activities in plasma, liver muscle and urine were determined with rats fed 10 to 12 g of 100 g body weight per day of the 10% casein diet (control) and 10% casein diets containing 7% glycine with or without 1.4% l-arginine HC1 and l-methionine for 7 days.

Nine hours after the final feeding, the amount of liver glycogen was high in the order of rats fed 10% casein diet containing 7% glycine, 10% casein diet containing 7% glycine with l-arginine and l-methionine, and the control. The amount of muscle glycogen was decreased only in those fed the control diet. The amount of liver lipid was increased by the addition of l-arginine and l-methionine to the excess glycine diet. Plasma and urinary urea was increased in animals given the excess glycine diets with or without both amino acids. In plasma liver, and muscle of animals given either of both the excess glycine diets 3 and 9 hr after the feeding, in general, glycine and serine were increased, and threonine and alanine were decreased as compared with those of rats given the control diet. However, the increase of glycine in plasma, liver and muscle detected at 9 hr after feeding the excess glycine diet was slightly prevented by the supplementation of both amino acids to the excess glycine diet. The activities of liver glycine oxidase and ornithine δ-aminotransferase of rats given the excess glycine diet with both amino acids were higher than those of other dietary groups. Liver serine dehydratase and glutamate-oxalacetate transaminase activities were high in the order of the animals fed the control, the excess glycine diet and the excess glycine diet containing both amino acids. Glutamate-pyruvate transaminase activity in the liver of rats fed the excess glycine diets with or without both amino acids were markedly higher than that of those fed the control. The activities of phosphopyruvate carboxylase and aconitase in the liver of animals given the excess glycine diet were higher than those of other dietary groups. Liver pyruvate kinase and glutamate dehydrogenase activities were similar among those dietary groups.     

Changes in Creatine and Urea Formation in Rats Fasted and Fed Low Protein Diets

Changes in the time course of the urinary excretion of creatinine, creatine and urea, and the activities of kidney transamidinase and liver urea-cycle enzymes were investigated in rats fasted and fed on a 10% casein diet and 10% casein diets supplemented with 10% glycine and/or 1.4% arginine.

The urinary total-creatinine of the fasted rats increased extremely during fasting for 7 days, while that of the animals given the 10% casein diet supplemented with glycine and arginine rose exceedingly on the 3rd day and thereafter no significant change was observed. Most of the increase of total-creatinine could be accounted for by the increase of creatine. The activity of kidney transamidinase in the fasted rats decreased in the 3rd day and thereafter kept nearly constant. The transamidinase activity of rats fed on the 10% casein diet after giving a protein-free diet for 5 days increased in the 3rd day. An inverse relation was observed between the urinary creatine and the transamidinase activity. The urinary urea increased in the rats fasted or fed on the 10% casein diets with the supplement of glycine and/or arginine. In fasting, the activities of liver urea-cycle enzymes, except arginase, had a tendency of increasing with the lapse of time. The arginase activity remained more or less constant. The reason of the extreme increase of urinary creatine during starvation was discussed.     

Studies on lipogenesis in vivo. Lipogenesis during extended periods of re-feeding after starvation

1. Lipogenesis was studied in mice re-fed for up to 21 days after starvation. At appropriate times [U-(14)]glucose was given by stomach tube and incorporation of (14)C into various lipid fractions measured. 2. In mice starved for 48hr. and then re-fed for 4 days with a diet containing 1% of corn oil, incorporation of (14)C from [U-(14)C]glucose into liver fatty acids and cholesterol was respectively threefold and eightfold higher than in controls fed ad libitum. The percentages by weight of fatty acids and cholesterol in the liver also increased and reached peaks after 7 days. Both the radioactivity and weights of the fractions returned to control values after 10-14 days' re-feeding. These changes could be diminished by re-feeding the mice with a diet containing 20% of corn oil. Incorporation of (14)C from [U-(14)C]glucose into extrahepatic fatty acids (excluding those of the epididymal fat pads) was not elevated during re-feeding with a diet containing either 1% or 20% of corn oil. However, incorporation of (14)C from [U-(14)C]glucose into the fatty acids of the epididymal fat pads was increased in mice re-fed with either diet, as compared with non-starved controls. 3. Lipogenesis was also studied in mice alternately fed and starved. Mice given a diet containing 1% of corn oil for 6hr./day for 4 weeks lost weight initially and never attained the weight or carcass fat content of controls fed ad libitum. Incorporation of (14)C from dietary [U-(14)C]-glucose into the fatty acids of the epididymal fat pads was elevated threefold in the mice allowed limited access to food, although the incorporation into the remainder of the extrahepatic fatty acids was not different from that found for controls. Mice given a diet containing 20% of corn oil for 6hr./day adapted to the limited feeding regimen quicker and in 4 weeks did attain the weight and carcass fat content of controls. Incorporation of (14)C from [U-(14)C]glucose into the fatty acids of the epididymal fat pads and the remainder of the extrahepatic fatty acids was respectively fivefold and threefold higher than in controls fed ad libitum. 4. The elevation in liver lipogenesis during re-feeding was greatest on a diet containing 1% of corn oil, whereas in extrahepatic tissues the increase in lipogenesis was greater when the mice were re-fed or were allowed limited access to a diet containing 20% of corn oil. These results suggest that the causes of the increased rate of incorporation of (14)C from [U-(14)C]glucose into fatty acids during re-feeding may be different in liver from that in extrahepatic tissues.     

Effects of Dietary Polychlorinated Biphenyls and Protein Level on Liver and Serum Lipid Metabolism of Rats

The effects of polychlorinated biphenyls (PCB) and dietary protein level on the liver and serum lipid metabolism of rats were studied. Rats were fed an experimental diet containing 7 or 30% casein with or without 0.1 % PCB for 24 days. Dietary PCB increased the level of triglyceride, phospholipid and cholesterol in the liver. The accumulation of triglyceride and cholesterol in liver was markedly increased with a low protein diet. The incorporation of injected ³H₂O into liver cholesterol was increased by PCB, but not affected by the dietary level of protein. The incorporation of the tracer into liver fatty acids was not increased by PCB intake. Dietary PCB also raised serum cholesterol and phospholipid, while PCB decreased triglyceride level, especially in rats on low protein diet. In addition, PCB intake clearly raised serum high density lipoprotein and diminished very low density lipoprotein. In the low protein group, PCB markedly repressed the incorporation of ³H₂O into serum lipids. The results suggest that the hepatic lipids accumulation by the addition of 0.1 % PCB to a low protein diet might be mainly ascribed to a repression in the transport of triglyceride from liver to blood. KEY WORDS: PCB, dietary protein, liver lipids, serum lipoprotein.     

Nature of DNA and RNA Degradation in Escherichia coli Induced by Colicin E2

Lipogenesis in the fatty liver of rat, which was induced by feeding an amino acid unbalanced diet containing 8% casein supplemented with 0.3% dl-methionine, has been studied by measuring the incorporation of glycerol-1-¹⁴C, palmitate-1-¹⁴C, citrate-1,5-¹⁴C, pyruvate-1-¹⁴C and pyruvate-2-¹⁴C into various lipid fractions and ¹⁴CO₂ during in vitro incubation of liver slices.

The total radioactivity of liver lipid per 100 g of the body and the incorporation of each substrate into triglyceride in the lipid were significantly higher in the imbalance group than the control group. Conversion of each substrate to ¹⁴CO₂ was not imparied in the imbalance group.

It is evident from these results that the induction of this type of fatty liver is due mainly to the triglyceride synthesis by both the fatty acid synthesis and the transesterification of fatty acid.

These results are considered to support the previous assumption in which acetate-1-¹⁴C was used as a precursor.     

Carbohydrate metabolism in liver from foetal and neonatal sheep

1. During development of the sheep, the activities of UDP-glucose–α-glucan glucosyltransferase and UDP-glucose pyrophosphorylase and the glycogen content are highest in the liver of lambs 2 weeks old and considerably lower in liver from adult sheep. 2. The activity of hexokinase and the rate of incorporation of [¹⁴C]-glucose into glycogen are much lower in liver from postnatal sheep than in rat liver. 3. The activities of hexose diphosphatase and glucose 6-phosphatase and the rates of incorporation of [¹⁴C]pyruvate and [¹⁴C]propionate into glycogen increase from low levels in the liver of foetal sheep to maxima a few weeks after birth. The activities in the liver of adult sheep are slightly lower. 4. The incorporation rate of [¹⁴C]pyruvate into glucose has been measured in liver slices from rats, sheep and chick embryos at several ages of these animals. This pathway is active in liver from foetal sheep, embryonic chicks and postnatal rats or sheep, but is absent from the liver from foetal rats. 5. Fructose metabolism, as measured by the rates of incorporation of [¹⁴C]fructose into glycogen and glucose in liver slices and by assays of liver ketohexokinase, is barely detectable in the liver of foetal sheep and appears soon after birth. 6. During development of the sheep, the incorporation rate of [¹⁴C]galactose into glycogen in liver slices is highest in foetal sheep and decreases with increasing age of the animal. 7. These findings are discussed with reference to the changing pattern of carbohydrate metabolism during neonatal development of liver in the sheep.     

Rapid dephosphorylation of eIF4E by dietary protein in the skeletal muscle and liver of food-deprived rats

The effect of dietary protein on eIF4E phosphorylation was examined in rats starved for 18 h and then fed on either a 20% casein diet (20C) or a protein-free diet (0C). Refeeding with the 20C diet, but not the 0C diet, resulted in partial dephosphorylation of eIF4E in both the skeletal muscle and liver. The results suggest that the dephosphorylation of eIF4E in response to food intake was regulated by the increase in plasma amino acid concentration that occurred after feeding with the 20C diet.     

Studies in lipogenesis in vivo: Fatty acid and cholesterol synthesis during starvation and re-feeding

1. Lipogenesis in vivo has been studied in mice given a 250mg. meal of [U-¹⁴C]glucose (2·5μc) or given an intraperitoneal injection of 25μg. of [U-¹⁴C]glucose (2·0μc). 2. The ability to convert a [U-¹⁴C]glucose meal into fatty acid was not significantly depressed by 6–7hr. of starvation. In contrast, incorporation of ¹⁴C into fatty acid in the liver after the intraperitoneal dose of [¹⁴C]glucose was depressed by 80% and by more than 90% by 1 and 2hr. of starvation respectively. Carcass fatty acid synthesis from the [U-¹⁴C]glucose meal was not depressed by 12hr. of starvation, whereas from the tracer dose of [U-¹⁴C]glucose the depression in incorporation was 80% after 6hr. of starvation. 3. Re-feeding for 3 days, after 3 days' starvation, raised fatty acid synthesis and cholesterol synthesis in the liver fivefold and tenfold respectively above the levels in non-starved control mice. These increases were associated with an increased amount of both fatty acid and cholesterol in the liver. 4. After 18hr. of starvation incorporation of a [U-¹⁴C]glucose meal into carcass and liver glycogen were both increased threefold.     

Metabolic shift from lipogenesis to glycogenesis in the last instar larval fat body of the silkworm,Bombyx mori

When [¹⁴C]glucose was injected into the last instar larvae of the silkworm, Bombyx mori, the label was incorporated into various tissues at varying degrees depending on the developmental stages. Fat body exhibited high incorporation rates throughout the feeding periods. Silk glands became active in incorporation but midgut decreased toward larval maturation. The pulse labeling experiment clearly demonstrated that the metabolic shift from lipogenesis to glycogenesis occurred in fat body at the middle of the last instar; a predominant incorporation was found in lipids when [¹⁴C]glucose was injected at the early stage, while at the late stage glycogen synthesis became most active. Incorporation into fat body proteins was not a major factor throughout the instar. Extirpation of silk glands enhanced incorporation into glycogen and proteins at the late stage but did not affect lipid synthesis. Long-term chase showed that fat body lipids and proteins synthesized at the early stage were totally carried over into the pupal fat body, while much glycogen produced at the late stage was used during the larval-pupal transformation with the remainder carried over into the pupa.From these results the metabolic shift from lipogenesis to glycogenesis in fat body is discussed in relation to the storage function of the fat body for pupal metamorphosis.     

Effects of Dietary Casein and Adrenal Hormone on the Dietary Induction of α-Amino-β-carboxymuconate-ε-semialdehyde Decarboxylase Activity in Rat

The effects of dietary casein and adrenal hormone on the dietary induction of α-amino-β-carboxymuconate-ε-semialdehyde decarboxylase (ACMSDase) activity in rat liver and kidneys were examined. Of three levels of casein in the diet examined (7.5%, 15% and 30%), only the feeding of a 30% casein diet to normal rats after three days on a protein-free diet resulted in a significant increase in the activity of ACMSDase in liver and kidneys on the following morning. The degree of the increase in this activity was higher in the liver than the kidneys. Dietary induction of ACMSDase activity disappeared when rats were adrenalectomized six days prior to the start of the experiment. In sham-operated rats, dietary induction of liver ACMSDase activity was as high as that in normal rats, however, that in kidneys disappeared. Prednisolone (synthetic adrenal hormone with glucocorticoid activity) injection of adrenalectomized rats led to the recovery of the dietary induction of liver ACMSDase activity. Blood serum corticosterone levels in normal rats on the last day of the feeding period remained maximum and then decreased gradually until 04:00, and tended to be higher in rats fed a protein-free diet than in those fed a 30% casein diet. These results suggest that the dietary induction of ACMSDase activity occurs only when a sufficient amount of dietary casein is ingested in the presence of a physiologically significant concentration of blood serum glucocorticoid in rats.