Fish protein hydrolysates affect cholesterol metabolism in rats fed non-cholesterol and high-cholesterol diets

Fish consumption is well known to provide health benefits in both experimental animals and human subjects. Numerous studies have demonstrated the beneficial effects of various protein hydrolysates on lipid metabolism. In this context, this study examined the effect of fish protein hydrolysates (FPH) on cholesterol metabolism compared with the effect of casein. FPHs were prepared from Alaska pollock meat using papain as a protease. Male Wistar rats were divided into the following four dietary groups of seven rats each: either casein (20%) or FPH (10%)?+?casein (10%), with or without 0.5% cholesterol and 0.1% sodium cholate. Serum and liver lipid levels, fecal cholesterol and bile acid excretions, and the hepatic expression of genes encoding proteins involved in cholesterol homeostasis were examined. In rats fed the FPH diets compared with casein diets with or without cholesterol and sodium cholate, the indexes of cholesterol metabolism-namely, serum cholesterol, triglyceride, and low-density lipoprotein-cholesterol levels-were significantly lower, whereas fecal cholesterol and bile acid excretions were higher. Rats fed the FPH diets compared with casein with cholesterol exhibited a lower liver cholesterol level via an increased liver cholesterol 7α-hydroxylase (CYP7A1) expression level. This study demonstrates that the intake of FPH has hypocholesterolemic effects through the enhancement of fecal cholesterol and bile acid excretions and CYP7A1 expression levels. Therefore, fish peptides prepared by papain digestion might provide health benefits by decreasing the cholesterol content in the blood, which would contribute to the prevention of circulatory system diseases such as arteriosclerosis.     

High-fat diets affect the expression of nuclear retinoic acid receptor in rat liver

The purpose of this study was to differentiate between the effects of the amount and the type of dietary lipids on the expression of the retinoic acid receptor (RAR), but also the peroxisome proliferator-activated receptor (PPAR) and the receptor of the 9-cis retinoic acid (retinoid X receptor (RXR)) in rat liver. Six groups of eight rats (5-weeks old) were fed during 4 weeks on the following diets: control 50 g vegetable oil/kg, high-fat diet 250 g vegetable oil/kg. These oils were either coconut oil (rich in saturated fatty acids) or olive oil (rich in monounsaturated fatty acids) or safflower oil (rich in polyunsaturated fatty acids, mainly as n-6). The three high-fat diets induced a significant decrease of the maximal binding capacity of RAR and of the abundance of RAR beta mRNA. Simultaneously, an increased expression of PPAR alpha mRNA was observed while no significant difference on abundance of RXR alpha mRNA was observed. The mechanisms involved are probably multiple, but one hypothesis is that a modification of the equilibrium between the nuclear receptors, resulting from an increased expression of PPAR, induces a decreased expression of RAR in rat liver.     

Cellular energy metabolism in rats receiving diets contaminated with lindane]

Young male rats, Wistar CF strain, about 70 g body weight, were fed a well-balanced diet containing 0 (control), 60 or 240 ppm lindane. The day before the experiment, all the animals were fasted, and some of them placed in a restraint wheel forcing them to walk on during 18 hrs; another group was given an i.p. injection of 2.6 g/kg glucose 30 minutes before their sacrifice. The redox and energy potentials of liver and muscle tissues were estimated after the determination of the following compounds: lactate, pyruvate, beta-hydroxybutyrate, acetoacetate, ATP, ADP, AMP, inorganic phosphate, NADP and NADPH. No effect of lindane was observed on muscle metabolism and the 60 ppm dose was without significant effect on liver metabolism. At the 240 ppm dosage: a. Lindane ingestion increased the liver betaHOB/AcAc ratio and decreased the Lac/pyr ratio. The ATP/ADP ratio was not significantly lowered, although the ATP concentration was diminished and, conversely, the AMP and inorganic P ones were elevated; b. Whereas lindane lowered the glucose effect on the mitochondrial redox potential, it had no influence on the increasing of the ATP/ADP ratio by glucose, or on the antiketogenic effect of this sugar; c. In the animals fed the lindane-contaminated diet, muscular exercise increased the liver betaHOB/AcAc and NADPH/NADP ratios, while the lac/pyr and ATP/ADP ratios were unaltered. But blood pyruvate was increased. The following interpretation has been given. Lindane ingestion inhibits liver mitochondrial activity and increases ketogenesis. The glucose treatment results in a poor glucose utilization for energy needs in the contaminated animals and the forced muscular exercise shows that gluconeogenesis proceeds at a slower rate than in the controls. It is suggested that an increased demand in NADPH, as resulting from the induction of the microsomal enzymes by lindane, is one of the mechanisms by which the pesticide inhibits the activity of the tricarboxylic acid cycle.     

Glyceride stearic acid content and structure affect the energy available to growing rats

To better understand the relative absorption of 18:0, specific structured triglycerides (STG) with varied ratios of 18:0 and short-chain organic acids (2:0, 3:0, 4:0) were compared with naturally occurring 18:0 in cocoa butter and to other mono- and diglycerides (DGs) containing 18:0. A bioassay for available fat energy was developed for growing Sprague-Dawley rats fed reduced energy from a control diet containing an American Heart Association (AHA) fat blend to generate 60 or 80% normal growth. The resulting standard growth curve was applied to the test fats, including cocoa butter and six glycerides, which were blended 3:1 with the AHA blend (to ensure EFA sufficiency) and pair-fed to match intake of control rats (AHA diet, 80% normal growth). Available energy from test fats ranged from 30 to 12 kJ/g (7.1 to 2.9 kcal/g) for cocoa butter to 18:0-DG, respectively, with the mean of the four different STG being 22 kJ/g (5.2 kcal/g). Energy available from test fats was negatively related to total 18:0 in the STG (r = -0.90; P < 0.001) and fecal dry weight (r = -0.92; P < 0.001); the effect was greater for monoglyceride (monolong-18:0) than for DG (dilong-18:0) but was not related to fecal 18:0. Compared with monoglyceride-18:0, available energy was increased or decreased when short-chain organic acids (SCOA) were added to form triglycerides, depending on the addition of butyrate or acetate, respectively. The different fat sources altered the available energy without apparent changes in lipoproteins or body composition. Thus, the reduced energy available from a glyceride containing 18:0 is determined by its total 18:0 and reflects the mono- or dilong chain character of the glyceride, its content of SCOA and triglyceride structure or organization per se.     

The role of gut tissue in the energy metabolism of growing lambs fed forage or concentrate diets

The role of the gastrointestinal tract (GIT) in explaining the less efficient utilization of metabolizable energy (ME) in growing lambs fed forage rather than concentrate-based diets was investigated by feeding forage (legume-grass silage) and concentrate (whole shelled maize) diets, at isoenergetic intakes (ME basis), using five groups of lambs. One group of seven lambs was an initial slaughter group and of the two groups (eight lambs per group) fed each diet, one group was fed for 8 weeks, whereas the other group was fed for 16 weeks. All lambs were slaughtered between 18.5 and 20 h following their last meal. Retained energy (as a percentage of ME intake) was higher (concentrate-fed 28, forage-fed 17; P<0.001) for the concentrate-fed animals. Weight-specific mucosal O2 uptake (ml/g DM per h), measured in vitro, was 37 % higher for the forestomach (reticulum, rumen and omasum) and small intestine (jejunum) than for the abomasum and large intestine (caecum and colon), but there was no evidence for a diet effect (except colon; forage-fed 5.3, concentrate-fed 4.2; P=0.036). Total GIT heat loss was estimated as 14 (forage-fed) and 18 (concentrate-fed) % of the whole-body heat loss. Although the GIT did not contribute to increased thermogenesis in the forage-fed lambs in the present study, greater relative contribution of GIT tissue to whole-body mass, i.e. GIT as a percentage of empty-body weight(forage 7.6, concentrate 6.6; P<0.001) in the forage-fed animals supports a role for the GIT in contributing to higher thermogenesis observed in ruminants fed forage as opposed to concentrate diets.     

低聚半乳糖与聚葡萄糖联用对生长期大鼠钙代谢和骨量的影响

目的 探究低聚半乳糖(galacto - oligosaccharides,GOS)与聚葡萄糖（polydextroses,PD）联用对生长期大鼠骨代谢和骨钙含量的影响。方法 60只刚断乳SD大鼠随机分为低钙组（饲料钙0.15%）、正常组（饲料钙0.5%）、强化组（饲料钙0.375% + 维生素D强化）、低比组（强化组饲料 + PD 2.5% + GOS 2.5%）和高比组（强化组饲料 + PD 4% + GOS 1%）5个组,分别饲喂含钙、维生素D3和益生元含量不同的饲料。观察大鼠一般情况,记录体重,于实验第83 d进行3 d的钙代谢实验,原子吸收法检测饲料、粪便和尿液中的钙含量,计算钙表观吸收率和储备率;喂饲93 d后处死,取心肝脾肾称重计算脏器系数,取血清测定血清钙、磷水平,取股骨测股骨干重,并采用原子吸收法测量股骨钙含量。结果 实验结束时,正常组、低比组和高比组体重均显著高于低钙组;各组的钙表观吸收率和钙储留率显著低于低钙组;与低钙组比较,各组的血清钙和骨钙含量都显著增加;低比组和高比组的股骨重和骨钙含量显著高于强化组,与正常组无显著差异。结论 充足的钙摄入对生长期大鼠的钙代谢及骨骼生长具有重要意义;聚葡萄糖和低聚半乳糖联用可增加生长期大鼠的骨钙含量。     

Feeding low iron diets affects fluid preference in growing rats

The effect of dietary iron (ferrous sulfate) concentration on the intake of solutions of sodium saccharin, hydrochloric acid, quinine sulfate, sodium chloride, and potassium chloride was studied. Male Charles River CD weanling rats were divided into four groups and fed semi-synthetic iron-free diets supplemented with either 0, 10, 20 or 40 ppm ferrous sulfate. Using a 48 hour, two-bottle preference test, the rats fed the diet with 0 ppm (added) iron showed significantly higher preferences for sodium chloride and potassium chloride solutions compared with the other three groups. Total fluid intake also increased in rats given the unsupplemented diet. Water intake was not increased in this 0 ppm group when sodium was offered. Blood hemoglobin and hematocrit, serum iron and body weight were lowest in the group with 0 ppm added iron, yet neither adrenal weights nor serum zinc was affected by the dietary iron levels.     

Effect of omnivorous and vegan diets with different protein and carbohydrate content on growth and metabolism of growing rats

The purpose of this study was to observe, in a rat animal model, the short and medium term effects of vegan (VEG) or omnivorous (OMNI) diets with different energy partition between nutrients (zone or classic). Six different diets were administered, for 72?days to 120 growing male Sprague-Dawley rats: (i) VEG zone diet; (ii) VEG classic diet; (iii) OMNI zone diet; (iv) OMNI classic diet; (v) OMNI zone diet with added fibre and (vi) OMNI classic diet with added fibre. Zone diets (high protein and low carbohydrates), resulted in better growth , feed efficiency, lower blood glucose and insulin responses. VEG diets have lowered cholesterol blood level. Histopathological analysis evidenced no damage to liver and kidney tissue by the intake of any of the diet types. Further longer animal and human duration studies should be performed to exclude detrimental effect of higher protein diet.     

Eggshell fractions containing different particle sized affect mineral absorption but not bone mineral retention in growing rats

The purpose of this study was to compare the calcium (Ca) bioavailability from eggshell fractions containing different particle size to purified CaCO₃ in male growing rats. Mineral absorption, bone mineral concentration, and biomechanical properties were evaluated. Mean Ca absorption of rats fed with eggshell diets amounted to 56.2% of the ingested Ca, which is considered high. However, we observed lower Ca absorption in large-sized particle eggshell fraction (ES L) and small-sized particle eggshell fraction groups but similar Ca absorption in intermediate-sized particle eggshell fraction (ES M) compared with the CaCO₃ group. Rats that received ES M and ES L had higher P and Mg absorption than the CaCO₃ group. No changes were observed in the bone mineral deposition, weight or mechanical resistance. We conclude that eggshell Ca is well absorbed by the intestine and retained in bones of growing rats, being a low cost alternative to achieve adequate Ca ingestion.     

Calcium metabolism, intestinal calcium-binding protein, and bone growth of rats fed high protein diets

The rat was used as a model for investigating the mechanism by which the consumption of high diets causes calciuria. Using a combined balance and kinetics study, calcium (Ca) metabolism was studied in 56-day old male rats which had been consuming a control (18% casein) or a high protein (36% casein) diet for 2, 14, or 28 days. Urine Ca was significantly increased to 1.7 mg/day and 1.1 mg/day in rats which consumed the high protein diet for 2 or 14 days respectively. After 29 days of consuming the high protein diet, urinary Ca excretion was 0.7 mg/day, the same as that of controls. No other criteria of calcium metabolism were significantly affected by the high protein intakes. Intestinal calcium-binding protein activity was not affected by consumption of the 36% casein diet for 7 days, nor was bone mineralization after consumption of this diet for 32 days. Since the rat excretes a low percentage of dietary Ca via the urinary route, it is not a useful model for studying Ca kinetics in protein-induced calciuria.     

Trans fatty acids affect lipoprotein metabolism in rats

This study was designed to investigate the effects of oleic (CIS), palmitic (SAT) and trans fatty acids (TRANS) on cholesterol metabolism. Rats fed the TRANS diet had lower plasma total cholesterol (P < 0.005) and non-HDL-cholesterol (non HDL-C) concentrations (P < 0.005) compared with their CIS-fed counterparts. Plasma HDL-C was highest in rats fed the SAT diet (P = 0.01). An in vivo assay of reverse cholesterol transport (RCT) was performed whereby radiolabeled cholesterol was delivered to the liver as acetylated LDL and the reappearance of label into plasma and HDL was determined. Plasma radioactivity in TRANS-fed rats was lower than in their SAT-fed counterparts (P = 0.01), and consistent with the cholesterol distribution in plasma, the difference was due to lower [(3)H]-cholesterol in lower density lipoproteins. Despite diet-induced differences in the cholesterol and phospholipid concentrations and fatty acid composition of HDL, the amount of label in HDL did not differ among groups, suggesting that consumption of these diets resulted in HDL populations with similar capacity to participate in RCT. The present findings suggest that dietary trans fatty acids regulate the metabolism of apolipoprotein B-containing lipoproteins in rats and that the effect may be masked in species possessing high plasma cholesteryl ester transfer protein (CETP) activity. These results reinforce the important role of CETP activity in determining the distribution of plasma cholesterol in response to dietary trans fatty acids.     

Protein utilization and lysine metabolism in obese and non-obese growing rats

Efficiency of protein utilization and lysine metabolism were studied in growing rats of the Zucker 13M strain, both obese and lean, and in the Charles River CD strain. When graded levels of wheat gluten or wheat gluten supplemented with lysine were fed to these three types of rats, no significant differences in the efficiency of protein utilization were found. However, under these dietary conditions, the Zucker obese rats appeared to be about 167% more efficient in energy utilization than the Zucker lean rats or the Charles River strain. The response of liver lysine-ketoglutarate reductase to the dietary treatment was similar in these three types of growing rats. The enzyme activity was induced by dietary lysine. Rats fed a lysine-deficient purified diet had a significantly lower enzyme activity than those fed a protein-free diet indicating that the same adaptive mechanism for lysine conservation as previously observed in adult rats also occurred in the growing animal. Interaction between dietary and genetic factors on fatty liver was found in this study. The most severe fatty liver was observed in the Zucker obese rats fed the most lysine-deficient diet containing 8% wheat gluten protein.     

Metabolic status in growing rats fed isocaloric diets with increased carbohydrate-to-fat ratio

OBJECTIVE: A low-fat diet is hypothesized to be associated with significant weight loss. However, most previous studies have been limited to low-fat, low-calorie restrictive diets. This study evaluated the effect of isocaloric diets given "ad libitum" but different in relative amounts of fat and carbohydrate on body size, energy metabolism, body composition, insulin-like growth factor-1, and leptin serum levels in growing Wistar rats. METHODS: Weanling male rats were fed with one of three diets that contained a ratio of carbohydrate to fat of 1:1, 2:1, or 3:1. Food intake, body weight, body length, oxygen consumption, and body composition were measured at ages 21 to 50 d. Serum levels of insulin-like growth factor-1 and leptin were also determined. RESULTS: Energy intake was similar across groups. The ratio of body weight to body length remained adequate throughout the experimental period. However, groups that received 3:1 and 2:1 showed increased weight and progressive decreases in energy expenditure, body fat composition, and serum level of leptin, but the ratio of insulin-like growth factor-1 to body length was not affected. CONCLUSIONS: Dietary substitution of fat with carbohydrates contributes to weight gain by decreasing energy expenditure and possibly by decreasing leptin secretion.     

Differences in energy intake affect body composition and adipose tissue accretion in young growing piglets

From d 7 to d 32 of age, piglets were fed one of three diets that varied in energy content: LE, lowest; IE, intermediate; and HE, highest. The protein, vitamin and mineral content was constant, the fat content varied, and the amount fed was on a body-weight basis. Body fat, adipose tissue fat and adipocyte size were proportional to energy intake. Adipocyte distribution was bimodal at d 32; cells <25 μm in diameter represented 60% of the total in the LE group and 40% in the IE and HE groups. Composition of the body fat-free mass did not differ. Pigs from all three dietary groups were fed a high-energy diet from d 32 to d 57. At d 57, pigs from the LE group had larger adipocytes than pigs from the IE and HE groups. Adipocyte distribution appeared trimodal in all groups at d 57; cells <25 μm in diameter represented <40% of the total. The number of cells >25 μm was larger in the LE than in the IE and HE groups.     

Efficacy of phytosterols and fish-oil supplemented high-oleic-sunflower oil rich diets in hypercholesterolemic growing rats

Phytosterols (P) and fish-oil (F) efficacy on high-oleic-sunflower oil (HOSO) diets were assessed in hypercholesterolemic growing rats. Controls (C) received a standard diet for 8 weeks; experimental rats were fed an atherogenic diet (AT) for 3 weeks, thereafter were divided into four groups fed for 5 weeks a monounsaturated fatty acid diet (MUFA) containing either: extra virgin olive oil (OO), HOSO or HOSO supplemented with P or F. The diets did not alter body weight or growth. HOSO-P and HOSO-F rats showed reduced total cholesterol (T-chol), non-high-density lipoprotein-cholesterol (non-HDL-chol) and triglycerides and increased HDL-chol levels, comparably to the OO rats. Total body fat (%) was similar among all rats; but HOSO-F showed the lowest intestinal, epididymal and perirenal fat. However, bone mineral content and density, and bone yield stress and modulus of elasticity were unchanged. Growing hypercholesterolemic rats fed HOSO with P or F improved serum lipids and fat distribution, but did not influence material bone quality.