High Carbohydrate Fat-free Diet Research Articles

Coral calcium carried hydrogen ameliorates the severity of non-alcoholic steatohepatitis induced by a choline deficient high carbohydrate fat-free diet in elderly rats

Hydrogen has been reported to act as an antioxidant, anti-apoptosis and anti-inflammatory agent. Coral calcium carried hydrogen (G2-SUISO) is a safer and more convenient form of hydrogen agent than others. The mechanism underlying the hepatoprotective effects of G2-SUISO using an elderly non-alcoholic steatohepatitis (NASH) rat model was investigated. Two days after fasting, six-month-old elderly male F344/NSlc rats were given a choline deficient high carbohydrate fat-free (CDHCFF) diet from day 0 to day 3 as CDHCFF control group, and then switched to a normal diet from days 4 to 7 with or without 300 mg/kg G2-SUISO. Rats in each group were finally being sacrificed on day 3 or day 7. In the CDHCFF diet group, G2-SUISO decreased the liver weight-to-body weight ratio, the serum AST, ALT, total cholesterol levels, inflammatory infiltration, pro-inflammatory cytokine expression and lipid droplets with inhibiting lipogenic pathways by reducing sterol regulatory element-binding protein-1c, acetyl-CoA carboxylase and fatty acid synthase gene expression compared with the CDHCFF diet alone. G2-SUISO had beneficial effects of anti-apoptosis as well the down-regulation of pro-apoptotic molecules including NF-κB, caspase-3, caspase-9 and Bax. These findings suggest that G2-SUISO treatment exerts a significant hepatoprotective effect against steatosis, inflammation and apoptosis in elderly NASH rats.

A-7. 肝Glucose 6-Phosphate Dehydrogenaseの誘導に及ぼすCyclic AMPの作用

A-7. 肝Glucose 6-Phosphate Dehydrogenaseの誘導に及ぼすCyclic AMPの作用

The effect of varying ratios of docosahexaenoic acid and arachidonic acid in the prevention and reversal of biochemical essential fatty acid deficiency in a murine model

ObjectiveEssential fatty acids (EFA) are necessary for growth, development, and biological function, and must be acquired through the diet. While linoleic acid (LA) and alpha-linolenic acid (ALA) have been considered the true EFAs, we previously demonstrated that docosahexaenoic acid (DHA) and arachidonic acid (AA) taken together as the sole source of dietary fatty acids can prevent biochemical essential fatty acid deficiency (EFAD). This study evaluates the effect of varying dietary ratios of DHA:AA in the prevention and reversal of biochemical EFAD in a murine model. MethodsUsing a murine model of EFAD, we provided mice with 2.1% of daily caloric intake in varying DHA:AA ratios (1:1, 5:1, 10:1, 20:1, 200:1, 100:0) for 19 days in association with a liquid high-carbohydrate fat-free diet to evaluate the effect on fatty acid profiles. In a second experiment, we evaluated the provision of varying DHA:AA ratios (20:1, 200:1, 100:0) on the reversal of biochemical EFAD. ResultsMice provided with DHA and AA had no evidence of biochemical EFAD, regardless of the ratio (1:1, 5:1, 10:1, 20:1, 200:1, 100:0) administered. Biochemical EFAD was reversed with DHA:AA ratios of 20:1, 200:1, and 100:0 following 3 and 5 weeks of dietary provision, although the 20:1 ratio was most effective in the reversal and stabilization of the triene:tetraene ratio. ConclusionProvision of DHA and AA, at 2.1% of daily caloric intake in varying ratios can prevent biochemical evidence of EFAD and hepatic steatosis over the short-term, with a ratio of 20:1 DHA:AA most effectively reversing EFAD.

Impact de la maladie parodontale sur la pression artérielle des souris diabétiques

Diabetes-driven cardiovascular diseases represent a high challenge for developed countries. Periodontal disease is strictly linked to the aforementioned diseases, due to its Gram negative–driven inflammation. Thus, we investigated the effects of periodontal disease on arterial pressure during the development of diabetes in mice. To this aim, C57BL/6 female mice were colonized with pathogens of periodontal tissue (Porphyromonas gingivalis, Prevotella intermedia and Fusobacterium nucleatum) for 1month, whereas another group of mice did not undergo the colonization. Subsequently, all mice were fed a high-fat carbohydrate-free diet for 3months. Then, arterial pressure was measured in vivo and a tomodensitometric analysis of mandibles was realized as well. Our results show increased mandibular bone-loss induced by colonization with periopathogens. In addition, periodontal infection augmented glucose-intolerance and systolic and diastolic arterial pressure, parameters already known to be affected by a fat-diet. In conclusion, we show here that periodontal disease amplifies metabolic troubles and deregulates arterial pressure, emerging as a new axis of metabolic investigation.

Metabolic adaptation to a high-fat diet is associated with a change in the gut microbiota

ObjectiveThe gut microbiota, which is considered a causal factor in metabolic diseases as shown best in animals, is under the dual influence of the host genome and nutritional environment. This...

Liver mitochondrial properties from the obesity-resistant Lou/C rat

The first objective was to evaluate the influence of caloric intake on liver mitochondrial properties. The second objective was aimed at determining the impact of increasing fat intake on these properties. Lou/C rats, displaying an inborn low caloric intake and resistant to diet-induced obesity, were compared to Wistar rats fed either ad libitum or pair-fed. An additional group of Lou/C rats were allowed to increase their fat intake by adjusting their diet from a standard high carbohydrate low-fat diet to a high-fat carbohydrate-free diet. Hydrogen peroxide (H(2)O(2)) generation, oxygen consumption rate (J(O(2))), membrane potential (DeltaPsi), activity of respiratory chain complexes, cytochrome contents, oxidative phosphorylation efficiency (OPE) and uncoupling protein 2 (UCP2) expression were determined in liver mitochondria. H(2)O(2) production was higher in Lou/C than Wistar rats with glutamate/malate and/or succinate, octanoyl-carnitine, as substrates. These mitochondrial features cannot be mimicked by pair-feeding Wistar rats and remained unaltered by increasing fat intake. Enhanced H(2)O(2) production by mitochondria from Lou/C rats is due to an increased reverse electron flow through the respiratory-chain complex I and a higher medium-chain acyl-CoA dehydrogenase activity. While J(O(2)) was similar over a large range of DeltaPsi in both strains, Lou/C rats were able to sustain higher membrane potential and respiratory rate. In addition, mitochondria from Lou/C rats displayed a decrease in OPE that cannot be explained by increased expression of UCP2 but rather to a slip in proton pumping by cytochrome oxidase. Liver mitochondria from Lou/C rats display higher reactive oxygen species (ROS) generation but to deplete upstream electron-rich intermediates responsible for ROS generation, these animals increased intrinsic uncoupling of cytochrome oxidase. It is likely that liver mitochondrial properties allowed this strain of rat to display higher insulin sensitivity and resist diet-induced obesity.

Relation between colonic proglucagon expression and metabolic response to oligofructose in high fat diet-fed mice

Several data suggest that fermentable dietary fiber could play a role in the control of obesity and associated metabolic disorders. The aim of this study was to investigate the putative role of short chain fructo-oligosaccharide (OFS) – a non-digestible oligosaccharide – in mice fed a standard diet and in mice fed two distinct high fat diets inducing metabolic disorders associated to obesity. We confirmed, in mice, several effects previously shown in rats fed a standard diet enriched with OFS, namely an increase in total and empty caecum weight, a significant decrease in epididymal fat mass, and an increase in colonic and portal plasma glucagon-like peptide-1 (GLP-1), a phenomenon positively correlated with a higher colonic proglucagon mRNA level. Curiously, 4-week treatment with OFS added at the same dose induced different effects when added in the two different high fat diets. OFS decreased energy intake, body weight gain, glycemia, and epididymal fat mass only when added together with the high fat–carbohydrate free diet, in which OFS promoted colonic proglucagon expression and insulin secretion. Our results support an association between the increase in proglucagon expression in the proximal colon and OFS effects on glycemia, fat mass development, and/or body weight gain. In conclusion, dietary oligosaccharides would constitute an interesting class of dietary fibers promoting, in certain conditions, endogenous GLP-1 production, with beneficial physiological consequences. This remains to be proven in human studies.

Identification and Characterization of Murine SCD4, a Novel Heart-specific Stearoyl-CoA Desaturase Isoform Regulated by Leptin and Dietary Factors

Stearoyl-CoA desaturase (SCD) is the rate-limiting enzyme in the biosynthesis of monounsaturated fatty acids. Thus far, three isoforms of SCD (SCD1, SCD2, and SCD3) have been identified and characterized. Regulation of the SCD1 isoform has been shown to be an important component of the metabolic actions of leptin in liver, but the effects of leptin on SCD isoforms in other tissues have not been investigated. We found that although the mRNA levels of SCD1 and SCD2 were not affected by leptin deficiency in the hearts of ob/ob mice, the SCD activity and levels of monounsaturated fatty acids were increased, implying the existence of another SCD isoform. This observation has led to the cDNA cloning and characterization of a fourth SCD isoform (SCD4) that is expressed exclusively in the heart. SCD4 encodes a 352-amino acid protein that shares 79% sequence identity with the SCD1, SCD2, and SCD3 isoforms. Liver X receptor alpha (LXR alpha) agonists and a high carbohydrate fat-free diet induced SCD4 expression, but unlike SCD1, SCD4 expression was not repressed by dietary polyunsaturated fatty acids. SCD4 mRNA levels were elevated 5-fold in the hearts of leptin-deficient ob/ob mice relative to wild type controls. Treatment of ob/ob mice with leptin decreased mRNA levels of SCD4, whereas levels of SCD1 and SCD2 were not affected. Furthermore, in the hearts of SCD1-deficient mice, SCD4 mRNA levels were induced 3-fold, whereas the levels of SCD2 were not altered. The current studies identify a novel heart-specific SCD isoform that demonstrates tissue-specific regulation by leptin and dietary factors.

Heterogeneous metabolic adaptation of C57BL/6J mice to high-fat diet.

C57BL/6J mice were fed a high-fat, carbohydrate-free diet (HFD) for 9 mo. Approximately 50% of the mice became obese and diabetic (ObD), approximately 10% lean and diabetic (LD), approximately 10% lean and nondiabetic (LnD), and approximately 30% displayed intermediate phenotype. All of the HFD mice were insulin resistant. In the fasted state, whole body glucose clearance was reduced in ObD mice, unchanged in the LD mice, and increased in the LnD mice compared with the normal-chow mice. Because fasted ObD mice were hyperinsulinemic and the lean mice slightly insulinopenic, there was no correlation between insulin levels and increased glucose utilization. In vivo, tissue glucose uptake assessed by 2-[(14)C]deoxyglucose accumulation was reduced in most muscles in the ObD mice but increased in the LnD mice compared with the values of the control mice. In the LD mice, the glucose uptake rates were reduced in extensor digitorum longus (EDL) and total hindlimb but increased in soleus, diaphragm, and heart. When assessed in vitro, glucose utilization rates in the absence and presence of insulin were similar in diaphragm, soleus, and EDL muscles isolated from all groups of mice. Thus, in genetically homogenous mice, HFD feeding lead to different metabolic adaptations. Whereas all of the mice became insulin resistant, this was associated, in obese mice, with decreased glucose clearance and hyperinsulinemia and, in lean mice, with increased glucose clearance in the presence of mild insulinopenia. Therefore, increased glucose clearance in lean mice could not be explained by increased insulin level, indicating that other in vivo mechanisms are triggered to control muscle glucose utilization. These adaptive mechanisms could participate in the protection against development of obesity.

A new model of acute liver steatosis induced in rats by fasting followed by refeeding a high carbohydrate-fat free diet. Biochemical and morphological analysis.

Background/Aims: Dietary habits are often considered to be responsible for fatty liver, a common histological finding in human liver biopsies. The aim of the present work was to test the hypothesis that fasting followed by refeeding high carbohydrate-fat free diets in rats disrupts hepatic lipid homeostatis, leading to liver lipid accumulation and morphological alterations. Methods: Male Wistar rats were fasted for 48 h, then refed ad libitum with a high carbohydrate-fat free diet. Results: Six hours after refeeding, a slight micro-vascuolar steatosis, mainly located in zone I was observed, whereas later or in the process, macrovacuolar steatosis extended to all three zones of the hepatic lobules. The present paper also contributes information on the mechanism of fasting-high carbohydrate-fat free diet, diet-induced steatosis: we show that both circulating and de novo hepatic synthesized fatty acid availabilities are implicated in the disequilibrium between triglyceride synthesis and secretion. Conclusios: The results are discussed, taking into account the putative implication of carbohydrate-induced lipogenesis in human fatty liver, occurring in non-insulin-dependent diabetic or obese patients.

Developmental changes in mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase gene expression in rat liver, intestine and kidney

The tissue-specific expression of the mitochondrial 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) synthase gene was studied in 15-day-old suckling rats. The mRNA and protein were present in liver, intestine and kidney, but were absent from brain, heart, skeletal muscles, brown and white adipose tissues. Kidney-cortex mitochondria from suckling rats were able to produce low amounts of ketone bodies from oleate. Hepatic, intestinal and renal HMG-CoA synthase mRNA levels increased slowly during foetal life and markedly after birth. The postnatal increase in liver HMG-CoA synthase mRNA could be due to the increase in plasma glucagon levels, since it rapidly induced the accumulation of HMG-CoA synthase mRNA in cultured foetal hepatocytes. Hepatic, intestinal and renal HMG-CoA synthase mRNA levels remained elevated throughout the suckling period or in rats weaned on to a high-fat carbohydrate-free diet (HF), but decreased by 50% in the liver and totally disappeared from the intestine and the kidney of rats weaned on to a high-carbohydrate low-fat diet (HC). When HC-weaned rats were fed on a HF-diet for a week, HMG-CoA synthase mRNA was re-induced in the intestine and the kidney. The role of hormones and nutrients in the regulation of HMG-CoA synthase gene expression is discussed.

Quantitation of glucose-6-phosphate dehydrogenase mRNA by solution hybridization: Correlation with rates of synthesis

Rat liver glucose-6-phosphate dehydrogenase (G6PD) is one of several proteins involved in lipid metabolism whose synthesis is regulated by diet. In experiments reported here, rats were fasted or fed diets until a new steady state level of G6PD was produced. Livers were used to measure G6PD activity, synthesis and mRNA simultaneously. Since accurate quantitation of G6PD mRNA by Northern blots was found to be difficult in noninduced animals a new solution hybridization assay was also used. Noninduced rats have approx. One molecule of G6PD mRNA per liver cell. Changes in G6PD mRNA are larger than previously reported and, at the steady state, can completely account for the 33-fold change in G6PD activity and synthesis when fasted rats are refed a high carbohydrate diet. In contrast, a high fat carbohydrate-free diet does not increase G6PD mRNA and dibutyryl cAMP lowers G6PD mRNA. Since changes in G6PD synthesis and activity are closely correlated, degradation of G6PD is not significantly regulated.

A high carbohydrate-fat free diet alters the proportion of heparin-bound VLDL in plasma and the expression of VLDL-apoB-100 epitopes

High carbohydrate-fat free diets (CHO-diet) induce the secretion of increased numbers of very-low-density lipoprotein (VLDL) particles and alter the composition and metabolism of VLDL. The aims of this study were to examine VLDL in greater detail, specifically to document any CHO-diet-induced alterations of apolipoprotein B-100 (apoB-100) epitope expression of VLDL, and any changes induced in subclasses of VLDL, as defined by heparin Sepharose chromatography. Fifteen normolipidemic subjects participated in the study by eating a basal typical American diet for 7 days and high carbohydrate diet (85% carbohydrate, <1% fat) for another 7 days. The sequence was changed in seven subjects. Fasting blood samples were analyzed for lipoprotein lipid and apoprotein concentrations. Heparin affinity VLDL subclasses were characterized chemically and electrophoretically [sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE)]. Immunoreactivities of apoB in VLDL were tested in solid phase competitive-binding radioimmunoassays (RIAs) using five monoclonal anti-B antibodies that react with defined epitopes of apoB-100. The CHO diet produced consistent increases of plasma triglycerides in all subjects by a mean of 66% and decreases in plasma cholesterol by 18%. ApoB in plasma decreased by 21% and apoA-I by 17%; however, apoE and ApoA-II did not change. VLDL was enriched with triglycerides (55.0% ± 0.8 v 57.0% ± 0.7, P < .05) and apoE (3.7% ± 0.5 to 5.9% ± 0.7, P < .007) and the ratio between apoE and apoC in VLDL increased (0.15 ± 0.03 to 0.25 ± 0.03, P < .002). In RIAs with monoclonal antibodies (MoAbs) B1B3 and B1B6 that define epitopes located near the LDL receptor recognition region of apoB-100, CHO-VLDL showed decreased immunoreactivity (ED 50s, in μg/mL, rose from 3.9 ± 1.0 to 5.4 ± 1.6, P < .03 and 3.8 ± 0.9 to 6.4 ± 1.3, P < .02, respectively). RIAs using the other three MoAbs with epitopes located in the middle and near the amino terminus of apoB-100 demonstrated no significant changes. The proportion of VLDL not bound by the heparin column was increased from 0.137 ± 0.02 on the basal diet to 0.23 ± 0.03 on CHO diet ( P < .009) and the unbound CHO-VLDL contained more phosphatidylethanolamine relative to sphingomyelin (1.54 ± 0.2 to 2.32 ± −0.2, P < .009). Our data suggest that diets may have differential affects on these two subpopulations of VLDL.

High carbohydrate fat-free diet modulates epitope expression of LDL-apoB-100 and interaction of LDL with human fibroblasts.

High carbohydrate diets are known to increase the concentration of very low density lipoprotein (VLDL) and to lower the concentrations of low density lipoprotein (LDL) and high density lipoprotein (HDL) in plasma. Such diets also alter lipoprotein compositions and metabolism. The aims of the present study were to assess in detail the effects of a virtually fat-free high carbohydrate (CHO) diet (CHO greater than 85% and fat less than 1% of calories) on various aspects of LDL. Thirteen healthy normolipidemic volunteers ate a basal "American" diet and the CHO diet for 7 days each in a forward or reverse sequence. Fasting blood samples were drawn at the ends of each study period and analyzed for lipoprotein lipid and apolipoprotein concentrations. Compositions of LDL particles isolated by ultracentrifugation were characterized chemically, LDL sizes were assessed by nondenaturing gradient electrophoresis on 2-16% gels, and association and degradation of LDL with normal human skin fibroblasts were quantified in cell cultures. Immunoreactivities of apoB in LDL were tested in solid phase competitive binding radioimmunoassays using five monoclonal anti-LDL antibodies that reacted with defined epitopes of apoB-100. The study diet produced consistent decreases of LDL cholesterol and apoB concentrations by 25% and 17%, respectively. LDL compositions were altered. Mean LDL triglycerides increased 3% to 4% of total LDL mass (P less than 0.004), and LDL particle sizes decreased (P less than 0.01). In radioimmunoassays that contained monoclonal antibody B1B3, an antibody that inhibits binding of LDL to the LDL receptor, the mean ED50 value for LDL protein was reduced from 3.75 to 2.66 micrograms (P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Elevation of liver diacylglycerols and molecular species of diacylglycerols in rats fed a lipogenic diet.

The concentration of diacylglycerols in rat liver was measured by a newly developed procedure that entailed a) freeze-clamping of the liver in situ, b) lipid extraction with dimyristoylglycerol as an internal standard, c) thin-layer chromatography, and d) gas-liquid chromatography. Molecular species of diacylglycerol and total diacylglycerols were quantified. The average level of diacylglycerol in livers of chow-fed rats was 102 micrograms/g wet wt, equivalent to about 180 nmol/g wet wt. A high-carbohydrate fat-free diet, known to increase the rate of fatty acid synthesis, greatly increased the liver diacylglycerol concentration relative to the level observed in rats fed laboratory chow. Diacylglycerol molecular species that contained 16-carbon fatty acids were most markedly elevated. Liver triacylglycerol, free cholesterol, and esterified cholesterol were concurrently increased. Molecular species of triacylglycerols and cholesteryl esters that contained 16-carbon fatty acids were elevated to the greatest degree. The concentrations of total triacylglycerol and cholesteryl esters exhibited a high correlation in the livers of all animals studied, suggesting their coexistence in metabolic pools, predominantly the cores of lipid droplets and newly assembled very low density lipoprotein particles. The correlation of liver diacylglycerol and triacylglycerol contents in the chow-fed rats suggests that the diacylglycerol concentration may be a rate-determining factor in triacylglycerol synthesis when diacylglycerol levels are in the observed range of 70-150 micrograms/g wet wt. In conclusion, when the rates of fatty acid synthesis and hence triacylglycerol synthesis are increased in the liver, the steady state concentrations of diacylglycerols are also elevated.(ABSTRACT TRUNCATED AT 400 WORDS)

Roles of hormonal and nutritional factors in the regulation of rat liver alcohol dehydrogenase activity and ethanol elimination rate in vivo.

Fasting reduced the liver alcohol dehydrogenase (ADH) activity by 51% (p less than 0.001). Insulin, within 2 hr, increased the ADH activity found in fasted animals by 28% (p less than 0.02). Insulin administration failed to stimulate the reduced ADH activity in diabetic rats. However, ADH activity in the diabetic-fed rats decreased by 52-54% (p less than 0.001) compared to normal-fed rats regardless of whether they were meal-fed or refed the normal chow. Glucagon blocked by 15% (p less than 0.02) the increase in ADH activity associated with refeeding. Furthermore, insulin caused a marginal stimulation of ethanol elimination rate (EER) when administered to fasted rats. All these results imply that insulin and glucagon may not be the only determining factors in the control of liver ADH activity associated with fasting and refeeding. Meal-feeding or refeeding a high carbohydrate fat-free diet compared to the normal chow-diet caused 29% (p less than 0.001) and 36% (p less than 0.05) decreases in ADH activity, respectively. Concomitant decreases in EER caused by high carbohydrate fat-free diet feeding were also observed under identical conditions. These results raise the possibility that the amount and the type of carbohydrate may be crucial in the regulation of ADH and EER. Alternatively, the presence of fat may be important in maintaining the normal level of ADH and EER.

Decreased hepatic fatty acid oxidation at weaning in the rat is not linked to a variation of malonyl-CoA concentration.

In rats weaned on a high-carbohydrate diet, hepatic fatty acid oxidation capacity is decreased when compared to suckling rats. Previous studies (Benito et al., 1979) suggested that a malonyl-CoA-dependent mechanism could be at the origin of this decrease. Studies on isolated hepatocytes show that despite, respectively, a low and a high lipogenic rate in suckling and weaned rats, malonyl-CoA concentrations are similar in the two groups. This might be due to the lower ratio fatty acid synthetase/acetyl-CoA carboxylase (EC 6.4.1.2) activities during suckling than after weaning. Different rates of hepatic fatty acid oxidation despite similar malonyl-CoA concentrations can be explained by the 2.5-fold higher carnitine palmitoyltransferase I (EC 2.3.1.21) activity in suckling rats together with a 7-fold higher Ki for malonyl-CoA. This precludes a tight control of fatty acid oxidation by [malonyl-CoA] in suckling rats. Weaning on a high-fat carbohydrate-free diet abolishes the changes previously described for the kinetic characteristics of carnitine palmitoyltransferase I suggesting that nutritional modifications rather than a developmental stage are involved. Thus, during the suckling-weaning transition, a variation of [malonyl-CoA] is not responsible for the decrease in hepatic fatty acid oxidation. It involves, in addition, a decrease in carnitine palmitoyltransferase I activity and an increase of the sensitivity of this enzyme to malonyl-CoA.

Rapid synergistic interaction between thyroid hormone and carbohydrate on mRNAS14 induction.

Recent studies have shown that hepatic mRNAS14 responds rapidly to thyroid hormone administration. Moreover, this mRNA is known to increase in mass with the administration of a high carbohydrate fat-free diet. Therefore, it appears to share many of the same properties of the known hepatic lipogenic enzymes. Because the lipogenic enzymes display a synergistic interaction between thyroid hormones and carbohydrates, we investigated the kinetics of response of mRNAS14 to carbohydrate feeding, as well as its interaction with triiodothyronine (T3). We found that mRNAS14 responds rapidly to the dietary administration of sucrose in euthyroid rats, with a 2-fold increase within 30 min, and a 25-fold increase by 4 h. On the other hand, when given to hypothyroid rats, sucrose ultimately lead to only a 2-3-fold increase in the level of mRNAS14, attaining a level less than that found in starved euthyroid rats. The diminished response of mRNAS14 to sucrose in hypothyroidism could not be enhanced by insulin administration. However, administration of replacement doses of T3 (400 ng/100 g of body weight) immediately restored the rapid response to sucrose feeding. The response of sucrose and T3 was synergistic. Dose-response studies with T3 indicated that the rapid interaction between T3 and sucrose was limited by the occupancy of the T3 nuclear receptor. A similar synergistic response to T3 and glucose was noted in primary hepatocyte cultures, thus indicating that the synergism between these two stimuli is not due to changes in extrahepatic hormones or metabolites. Our data are most consistent with the hypothesis that the T3-nuclear receptor complex multiplies a signal generated by carbohydrate metabolism to induce hepatic mRNAS14. The interaction does not appear to require the preliminary induction of carbohydrate-metabolizing enzymes and their mRNAs.

Tissue-specific control of rat malic enzyme activity and messenger RNA levels by a high carbohydrate diet.

In euthyroid rats fed a high carbohydrate fat-free diet for 10 days, the mass of cellular malic enzyme mRNA in liver is increased 7- to 8-fold above the basal level. Malic enzyme activity is stimulated to the same extent. This effect does not result from an increase either in the transcriptional activity of the malic enzyme gene, as determined by nuclear run-off transcription assay, or in the content of intranuclear malic enzyme RNA sequences. Mathematical modeling shows that this increase in cytoplasmic mRNA is compatible with retarded degradation of cytoplasmic mRNA. Regulation of malic enzyme by carbohydrates is liver-specific, since no response is observed in the following nonhepatic tissues: brain, heart, spleen, kidney, testis, and lung. Furthermore, the amplitude of the response in liver depends on the thyroid state of the animals, being lower (by a factor of approximately 4) in hypothyroidism and higher (12- to 15-fold) when normal animals are injected simultaneously with a daily dose of 15 micrograms of triiodothyronine per 100 g of body weight for 10 days. Since thyroid hormones regulate liver malic enzyme synthesis predominantly at the nuclear level and carbohydrates at the cytoplasmic level, the additive effect of triiodothyronine and a high carbohydrate diet on the activity of malic enzyme is readily explicable.

Effect of weaning on different diets on hepatic gluconeogenesis in the rat.

The capacity of gluconeogenesis from lactate (10 mmol/l) was studied on isolated hepatocytes in 15-day-old suckling and in 28-day-old rats weaned at the age of 19 days on various diets. Weaning on a high-fat carbohydrate-free diet allowed to maintain a high gluconeogenic rate. By contrast, as soon as the carbohydrate content of the weaning diet was sufficient to meet the glucose needs of the newborn, the gluconeogenic capacity was reduced. The amount of fat in the weaning diet had no influence on the gluconeogenic capacity. Changes in the hepatic gluconeogenic rate at weaning were inversely correlated with the plasma insulin/glucagon molar ratio.