Metabolic effects in rats of a diet with a moderate level of medium-chain triglycerides.

Energy intake, weight gain, carcass composition, plasma fuels, hepatic metabolites and lipogenic enzyme activities were studied in adult rats fed either a low fat, high carbohydrate (LF) diet or one of two fat-containing diets in which 32% of the metabolizable energy was constituted by long-chain triglycerides (LCT) or medium-chain triglycerides (MCT). Compared with the LF diet, the MCT diet did not depress food and energy intake, weight gain, energy and nitrogen retention or lipid deposition and did not produce ketogenesis. The weight gain of rats fed LCT was 25% higher, and increased lipid deposition was observed.

Age-dependent glycolysis and gluconeogenesis enzyme activities in starved-refed rats.

Food intake, plasma glucose, insulin (I) and glucagon (G), hepatic glycogen and fructose 2,6-bisphosphate (F-2, 6-P2) and liver glucokinase, glucose 6-phosphatase (G6-Pase), 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (6-PF-2 kinase/F-2, 6-P2ase), pyruvate kinase (PK-L) and phosphoenolpyruvate carboxykinase (PEPCK) activities were measured in 2 and 22-month-old rats before 3 d starvation and after 2, 4, 6, 24 and 48 h refeeding a high carbohydrate (HC, 74% w/w) diet. Expressed per 100 g of body weight, the food intake of old rats was 55% lower than that of young rats and the amount of carbohydrate absorbed hourly during the first 6 h of refeeding was 2.4-fold higher in young than in old rats.

Metabolic changes in rats fed a low protein diet during post-weaning growth.

Metabolic changes in rats fed a low protein diet were investigated during 3 weeks after weaning using lactalbumin (LP) as dietary protein source. The energy intake was higher and the weight gain lower in rats fed the low protein diet (6%, LP group) than in control rats (13% lactalbumin, C group). Low protein diet induced no changes in plasma glucose, free fatty acids, or triacylglycerol concentrations; however, plasma protein and urea concentrations were lower in LP than in C rats.

Age-dependent hepatic lipogenic enzyme activities in starved-refed rats.

Food intake, plasma glucose, insulin (I) and triiodothyronine (T3) and liver glucose 6-phosphate dehydrogenase (G6P-DH), malic enzyme (ME). ATP-citrate lyase, acetyl-CoA carboxylase (AcCoACx) and fatty acid synthase (FAS) activities were measured in 2 and 22 months old rats before, after 3 d starvation and 2,4,6. 24 and 48 h refeeding a high carbohydrate (74% w/w) diet.

Effects of long-term feeding of high-protein or high-fat diets on the response to exercise in the rat.

The aim of this work was to find by which mechanisms an increased availability of plasma free fatty acids (FFA) reduced carbohydrate utilization during exercise. Rats were fed high-protein medium-chain triglycerides (MCT), high-protein long-chain triglycerides (LCT), carbohydrate (CHO) or high-protein low-fat (HP) diets for 5 weeks, and liver and muscle glycogen, gluconeogenesis and FFA oxidation were studied in rested and trained runner rats. In the rested state the hepatic glycogen store was decreased by fat and protein feeding, whereas soleus muscle glycogen concentration was only affected by high-protein diets.

Post-exercise glycogen resynthesis in trained high-protein or high-fat-fed rats after glucose feeding.

This study examined the effect on glycogen resynthesis during recovery from exercise of feeding glucose orally to physically trained rats which had been fed for 5 weeks on high-protein low fat (HP), high-protein/long-chain triglyceride (LCT) or high carbohydrate (CHO) diets. Muscle glycogen remained low and hepatic gluconeogenesis was stimulated by long-term fat or high-protein diets. The trained rats received, via a stomach tube, 3 ml of a 34% glucose solution immediately after exercise (2 h at 20 m.

Age-dependent changes in rat hepatic fructose 2, 6-bisphosphate, 6-phosphofructo-2-kinase/fructose 2, 6-bisphosphatase and pyruvate kinase activity in response to a high protein diet or starvation.

Plasma insulin (I), glucagon (G) and glucose, hepatic glycogen, fructose 2, 6-bisphosphate (F2, 6-P2), fructose 1, 6-bisphosphate, phosphoenolpyruvate, and some liver key enzymes involved in glycolysis (6-phosphofructo-2-kinase/fructose-2, 6-bisphosphatase (6-PF-2kinase/F-2,6-P2ase), activity ratio (velocity at suboptimal substrate concentration/maximum velocity) of pyruvate kinase (PK-L] and in gluconeogenesis (phosphoenolpyruvate carboxykinase activity) have been compared in young (2 months) and old (16 months) rats upon starvation or transition to a high protein (HP) diet. In the 10 and 24 hours after the dietary switch, plasma glucose decreased less and hepatic glycogen was less depleted in the old rats. The ratios of plasma I/G and of hepatic 6-PF-2kinase/F-2,6-P2ase were higher in the old rats and their decrease delayed at both time points, as was the concentration of hepatic F-2,6-P2 and the activity ratio of PK-L (before and after removal of endogenous noncovalent factors).

[Long-term consumption of a diet with moderate medium chain triglyceride content does not inhibit the activity of enzymes involved in hepatic lipogenesis in the rat].

The activities of glucose 6-phosphate dehydrogenase (EC 1.1.1.

Changes in rat hepatic fructose 2,6-bisphosphate and 6-phosphofructo-2-kinase/fructose 2,6-bisphosphatase activity during three days of consumption of a high protein diet or starvation.

Changes in plasma glucose, hepatic cyclic AMP, glycogen and fructose 2,6-bisphosphate (F-2,6-P2), and liver 6-phosphofructo-2-kinase (6-PF-2kinase), fructose 2,6-bisphosphatase (F-2,6-P2ase) and phosphoenolpyruvate carboxykinase (PEPCK) activities were examined in rats fed a low protein, high carbohydrate (HC) diet during 3 d of either starvation or feeding a high protein, carbohydrate-free (HP) diet. Under both HP feeding or starvation, liver cyclic AMP increased after 1 d and remained constant thereafter. Whereas plasma glucose was low during starvation, it was unaffected by HP feeding.

Metabolic effects induced by long-term feeding of medium-chain triglycerides in the rat.

Energy intake, weight gain, carcass composition, plasma hormones and fuels, hepatic metabolites and the activities of phosphoenolpyruvate carboxykinase (PEPCK), malic enzyme, and glucose 6-phosphate dehydrogenase (G6P-DH) were examined in adult rats during a 44-day period of low fat, high carbohydrate (LF) feeding or of consumption of one or two high (70% metabolizable energy) fat diets composed of 63% (metabolizable energy) long-chain (LCT) or medium-chain (MCT) triglycerides. Energy intake was similar in the LCT and MCT groups but was less than that of LF group. The weight gain of rats fed MCT diet was 30% less than that of rats fed LF or LCT diets.

Development of gluconeogenesis from various precursors in isolated rat hepatocytes during starvation or after feeding a high protein, carbohydrate-free diet.

Gluconeogenesis from dihydroxyacetone (DHA), glycerol, lactate, pyruvate or alanine was studied in the absence or in the presence of glucagon in hepatocytes isolated from starved rats or from rats fed a high protein diet for 2-48 h. In both groups, gluconeogenesis from DHA, glycerol, lactate and pyruvate exhibited similar changes over 48 h; the rates of glucose production increased progressively until 24 h and then plateaued. During the early phase (2-11 h), gluconeogenesis from DHA and glycerol were higher than gluconeogenesis from lactate and pyruvate.

Comparison between starvation and consumption of a high protein diet in rats: hepatic metabolites and amino acid levels during the first 24 hours.

Changes in hepatic levels of lactate, pyruvate, phosphoenolpyruvate, alpha-ketoglutarate, malate, oxaloacetate, adenine nucleotides, inorganic phosphate, ketone bodies, alanine, serine, glycine, aspartate, glutamate, valine and urea were examined in adult rats during the first 24 h of either starvation or consumption of a high protein (HP) diet. No differences were found between these two conditions in the concentration of metabolites studied or the cytosolic redox state. Under both conditions, the cytosolic phosphorylation state decreased to a low 15 h into the experiment but the changes were more pronounced on the HP diet.

Studies on the early changes in rat hepatic fructose 2,6-bisphosphate and enzymes in response to a high protein diet.

Pertinent hepatic metabolites and enzymes were examined in rats fed a high carbohydrate (HC) diet and during the first 24 h of either starvation or feeding a high protein (HP) diet. Consumption of the HC diet induced slight but definite 24-h oscillations in hepatic concentrations of cyclic AMP, glycogen, glucose 6-phosphate, fructose 2,6-bisphosphate, fructose 1,6-bisphosphate and phosphoenolpyruvate, as well as the activities of 6-phosphofructo-2-kinase/fructose 2,6-bisphosphatase and phosphoenolpyruvate carboxykinase. The transition to starvation or the HP diet induced, within 12 h, concurrent increases in cyclic AMP and phosphoenolpyruvate and decreases in glycogen, glucose 6-phosphate, fructose 6-phosphate, fructose 2,6-bisphosphate and fructose 1,6-bisphosphate.

Comparison between starvation and consumption of a high protein diet: plasma insulin and glucagon and hepatic activities of gluconeogenic enzymes during the first 24 hours.

Plasma insulin, glucagon, glucose, free fatty acids and glycerol, hepatic cyclic AMP and glycogen, and liver phosphoenolpyruvate carboxykinase (PEPCK), fructose 1,6-bisphosphatase (FBPase), glucose 6-phosphatase (G6Pase) and alanine amino transferase (AAT) activities were examined in adult rats during the first 24 h of either starvation or consumption of a high protein, carbohydrate-free (HP) diet. Under both nutritional conditions, plasma insulin fell within 12 h and remained constant thereafter. Glucagon increased 12 h after the start of the experiment and peaked between 18-24 h.

Gluconeogenesis from dihydroxyacetone in rat hepatocytes during the shift from a low protein, high carbohydrate to a high protein, carbohydrate-free diet.

Pyruvate kinase activity and rates of gluconeogenesis and glycolysis in rat hepatocytes were evaluated by production of glucose and lactate + pyruvate from dihydroxyacetone during the first 48 hours after the shift from a low protein, high carbohydrate diet to a high protein, carbohydrate-free diet. The effect of glucagon was also studied. In the absence of glucagon, 11-17 hours after the dietary shift when glycogen was lowest, gluconeogenesis was maximal and glycolysis minimal.

Metabolic effects of medium- or long-chain triglycerides and high-protein, carbohydrate-free diets in Zucker rats.

The effects of protein levels and types of fat in the diet on the metabolism of lean and obese Zucker rats were studied. For 40 days the rats were fed ad libitum one of four diets: two "usual protein" diets (19% protein by weight) with 19.4% triacylglycerols, either long chain (UP-LCT diet) or medium chain (UP-MCT diet); and two high protein (64% protein), carbohydrate-free diets, again with 19.

Metabolic effects of high-protein diets in Zucker rats.

The effects of dietary protein on the metabolism of proteins, carbohydrates, and especially, lipids were investigated in genetically obese Zucker rats and their lean siblings. For 40 days the rats received diets containing 15%, 64%, or 82% protein, included at the expense of cornstarch. In the obese animals, the high-protein diets led to decreased food intake and weight gain.

Effects of excess methionine ingestion on hepatic phosphate, adenine nucleotides and free amino acids in the rat.

Adult male rats were force-fed either a single dose of 200 mg of DL-methionine or an amino acid mixture with the pattern of casein. The animals were anesthetized with pentobarbital at 0, 1.5, 3 and 4 hours after intubation, and samples of liver were removed by a freeze-clamping technique at 0, 15 and 30 seconds of ischemia.

Circadian variation of liver metabolites and amino acids in rats adapted to a high protein, carbohydrate-free diet.

Diurnal variation in hepatic levels of lactate, pyruvate, phosphoenolpyruvate (PEP), alpha-ketoglutarate, malate, oxaloacetate, ketone bodies, alanine, serine, glycine, aspartate, glutamate, glutamine, valine, urea, adenine nucleotides and inorganic phosphate were studied in rats adapted to a high protein, carbohydrate-free diet for 24 days. Most circadian rhythms differed in relation to controls (10% protein diet); many merely had different amplitudes, some were inverted, and some exhibited drastically altered patterns. Cytoplasmic redox state exhibited nearly similar variations and phosphorylation state differed primarily in amplitude whereas mitochondrial redox state was highly depressed in the absorptive phase.

Hepatic metabolites and amino acid levels during adaptation of rats to a high protein, carbohydrate-free diet.

Changes in hepatic levels of lactate, pyruvate, phosphoenolpyruvate (PEP), alpha-ketoglutarate, malate, oxaloacetate, ketone bodies, alanine, serine, glycine, aspartate, glutamate, glutamine, valine, urea, adenine nucleotides and inorganic phosphate were examined in rats consuming a high protein, carbohydrate-free diet for up to 40 days. While some components showed transient changes, others (pyruvate, malate, oxaloacetate, PEP, ketone bodies, alanine, glycine, glutamine, valine, urea, adenine nucleotides and inorganic phosphate) were permanently altered. The cytoplasmic and mitochondrial redox states were only transiently affected and by day 24 were not different from control values.

Plasma glucagon and insulin concentrations and hepatic phosphoenolpyruvate carboxykinase and pyruvate kinase activities during and upon adaptation of rats to a high protein diet.

Plasma hormones, glucose and free fatty acids, liver glycogen and two key enzymes of glycolysis and gluconeogenesis were examined in adult rats during a 40-day period of high protein feeding. Plasma insulin fell within 1 day but returned to normal after 4 days. Glucagon changed more slowly, reaching a maximum on day 4 and declined to near the control value within 24 days.

Development of gluconeogenic enzymes in the liver of fasting or suckling newborn pigs.

Gluconeogenic enzymes and substrates were measured in the livers of fasted and suckled newborn pigs in the first 48 h postpartum. The activities at birth of glucose-6-phosphatase, fructose-1,6-diphosphatase, pyruvate carboxylase and phosphoenolpyruvate carboxykinase were, respectively, 70%, 45%, 117% and 35% of adult values. At birth, cytosolic phosphoenolpyruvate carboxykinase represented 35% of total activity, a similar distribution to that in the adult.

The effects of dietary self-selection upon the overshoot phenomenon in starved-refed rats.

The food intake, liver composition and hepatic activity of pyruvate kinase (PK), glucose-6-phosphate dehydrogenase (G6P-DH), malic enzyme (ME) and acetyl CoA carboxylase (AcCoA Cx) were studied in starved-refed rats. When rats were refed a mixed diet for 3 days, food intake significantly increased (by 33%) from day 1 to 3 and the glycogen accumulation was maximal after 24 hours, but decreased significantly by day 3 (by 34%). In contrast, liver triglycerides sharply increased (10-fold) from day 1 to 3.

Schedule of protein ingestion and circadian variations of glycogen phosphorylase, glycogen synthetase and phosphoenolpyruvate carboxykinase in rat liver.

The circadian rhythms of liver glycogen and hepatic activity of glycogen synthetase (GS), glycogen phosphorylase (GP) and phosphoenolpyruvate carboxykinase (PEPCK) were studied in adult male rats. The rats either received a mixed diet ad libitum (10% protein) or a protein meal (1.85 g protein) given at 09:00 or 21:00 hours, with free access to a protein-free diet (separately-fed).