The influence of dietary sodium on bone development in growing rats

The present study investigated the effects of dietary sodium on bone growth in young rats. Five-week-old rats were fed one of three different diets for 60 days: low sodium (NaCl, 0.32 g/kg diet), normal sodium (NaCl, 2.6 g/kg) and high sodium (NaCl, 20 g/kg). The proximal tibial metaphysis (PTM), the fifth lumbar vertebra (LV₅) and the middle part of the tibia shaft (TX) were analysed by bone histomorphometry. The expression of three osteogenesis genes, Runx2, osteopontin and osteocalcin, was determined by RT-PCR in bone samples from the skull. In both the PTM and LV₅, trabecular area and thickness were increased by the low-sodium diet, while the high-sodium diet decreased trabecular area in LV₅. Dynamic data revealed that sodium restriction increased bone formation parameters in the PTM and LV₅, but decreased bone resorption in LV₅. In TX, endosteal bone formation was enhanced by the low-sodium diet and depressed by the high-sodium diet compared to the normal sodium group. But there were no statistically changes in the cortical bone area of TX. Low-sodium intake significantly enhanced the expression of all three osteogenesis genes compared to the normal sodium group, while high-sodium intake suppressed osteogenic gene expression. Our results suggest that sodium restriction in growing rats promotes bone development by influencing both bone formation and resorption.     

Supplemental sodium phytate and microbial phytase influence iron availability in growing rats.

Five groups of individually housed albino rats (n = 7 each, initial average weight = 42 g) were fed diets based on corn starch and casein over a 4-week period. All diets were supplemented with 35 mg/kg of iron from FeSO4 x 7 H2O. Group I (control) was fed the basal diet free of phytic acid (PA) and phytase. By replacing corn starch by 7.5 g (groups II and IV) and 15 g phytic acid (groups III and V) from sodium phytate per kg diet, molar PA/iron ratios of 18 and 36 were obtained. In groups IV and V, 1000 U phytase from Aspergillus niger per kg diet were added. Food conversion efficiency ratio and growth rate as well as iron in plasma and spleen, hemoglobin, red blood cell count and erythrocyte zinc protoporphyrin were not influenced by the different dietary treatments. Dietary phytate reduced apparent iron absorption in groups II and III. Furthermore hematocrit, transferrin saturation and iron concentration in liver and femur were lowered in rats fed diets with PA, while total and latent iron-binding capacity of plasma increased. Microbial phytase supplementation (groups IV and V) partly counteracted the antinutritive effects of phytic acid on iron availability.     

The effect of swimming activity on bone architecture in growing rats

The effect of non-habitual physical activity on bone architecture in the rat humeral shaft was examined. Two groups of rats were trained to swim for 1 h a day, for 20 weeks, at two training levels. The control group consisted of sedentary rats. Parameters of cross-sectional bone morphology (cross-section areas, principal area moments of inertia and their ratio) were used to evaluate the response of bone architecture to mechanical loading. The strength of bone was assessed by measuring the ultimate compressive force and stress. The cortical cross-section area and principal moments of inertia were found to be significantly higher in the swimming groups than in the controls. Examination of the ratio between the major and minor moments of inertia revealed a pronounced change in the shape of the bone cross-section which became more rounded following swimming training. The ultimate compressive force was significantly higher in the swimming rats while the changes in ultimate stress were not significant. Our results indicate a gain of bone strength due to increased periosteal apposition and modified bone tissue distribution. The marked changes in bone morphology are attributed to the different nature of the forces and moments exerted on the humerus during swimming compared to those prevailing during normal locomotion.     

The influence of dietary protein on ascorbic acid metabolism in rats

1. d-Glucuronolactone reductase, l-gulonolactone oxidase, uronolactonase, dehydroascorbatase, l-gulonate dehydrogenase and l-gulonate decarboxylase have been measured in the tissues of rats fed on diets containing variable amounts of protein. Rats fed on a protein-free or a 2% casein diet for 15 days showed a marked decline in the activities of d-glucuronolactone reductase, l-gulonolactone oxidase, uronolactonase and dehydroascorbatase in the liver, and no change in l-gulonate dehydrogenase and l-gulonate decarboxylase activities in the kidney when compared with rats fed on diets containing 9%, 18% or 25% casein. Giving diets containing 60% or 88% casein to rats did not appreciably alter the activities of uronolactonase, dehydroascorbatase, l-gulonate dehydrogenase and l-gulonate decarboxylase, but inhibited considerably the activities of d-glucuronolactone reductase and l-gulonolactone oxidase in the liver, resulting in decreased synthesis of ascorbic acid. 2. Rats fed on a 25% casein diet showed maximal weight gain, higher tissue reserve of ascorbic acid and higher urinary excretion of both ascorbic acid and glucuronic acid when compared with rats fed on diets containing lower or higher amounts of protein.     

The effects of dietary boric acid on bone strength in rats

The effects of dietary boron (B) (from boric acid [BA]) on bone strength were evaluated using male F344 rats. B was administered by dietary admixture of BA to NIH-07 feed at concentrations of 200, 1000, 3000, and 9000 ppm. The latter two levels were found in previous studies to be reproductively toxic to both males and the developing fetus. The first two levels are below and just at, respectively, the levels for producing fetal malformations, and are below the dose required to produce male reproductive toxicity. Resistance to destructive testing was measured on femora, tibiae, and lumbar vertebrae. Although femur and tibia resistance to bending force were not affected by any amount of dietary B, vertebral resistance to a crushing force was increased by ≈10%, at all dose levels (200-9000 ppm). These data show that even levels of BA that are not reproductively toxic can affect the strength of the axial skeleton in rats.     

The influence of experimental deformation on craniofacial development in rats

Cranial deformation was produced experimentally in rats 8 to 40 days old for the purpose of studying the rotation of the craniofacial bones and the modification of the growth rates of the functional cranial components. One hundred and twenty four skulls (65 males and 59 females) were employed, classified as: deformed , deformed-hydrocephalic, sham-operated and controls. A midsagittal diagram was drawn for each skull and the angle subtended by each bone with respect to the vestibular plane was measured. Growth indices were worked out for both the neural skull and the facial skull. Deformation altered the rotation of the parietal, interparietal and basisphenoidal bones and restricted the rotation of the fronto-ethmo-facial complex. Alteration of the longitudinal growth rates of the dorsal and basilar components of the neurocranium and the splanchnocranium produced the persistence of the klinorynchal state.     

Sympathectomy alters bone architecture in adult growing rats

Sympathetic nervous system (SNS) fibres and alpha- and beta-receptors are present in bone, indicating that the SNS may participate in bone metabolism. The importance of these observations is controversial because stimulation or inhibition of the SNS has had various effects upon both anabolic and catabolic activity in this tissue. In this study we evaluated the effects of pharmacological sympathectomy, using chronic treatment of maturing male rats with 40 mg of guanethidine/kg i.p., upon various parameters in bone. Double labelling with tetracycline injection was also performed 20 and 2 days before sacrifice. Bone mass, mineral content, density and histomorphometric characteristics in different skeletal regions were determined. Bone metabolic markers included urinary deoxypyridinoline and serum osteocalcin measurements. Guanethidine significantly reduced the accretion of lumbar vertebral bone and of mineral content and density, compared to controls. Femoral bone mineral content and density were also significantly reduced, compared to controls. Histomorphometric analyses indicated these effects were related to a reduction of cortical bone and mineral apposition rate at femoral diaphysials level. Both markers of bone metabolism were reduced in controls as they approached maturity. Guanethidine significantly decreased serum osteocalcin compared to controls, while urinary deoxypyridinoline was unchanged. These data indicate that guanethidine-induced sympathectomy caused a negative balance of bone metabolism, leading to decreased mass by regulating deposition rather than resorption during modeling and remodeling of bone.     

The influence of sodium metavanadate on the process of diabetogenesis in BB rats

Vanadium has been shown to be beneficial in the oral treatment of animal models of type 1 and type 2 diabetes. The aim of the study was to evaluate the short-term effects of sodium metavanadate in prediabetic BB-DP rats. To do this, 96 rats were divided into 4 equal groups. Groups VI, V2, V3 were treated with sodium metavanadate (0.1, 0.2 and 0.3 mg/ml respectively) and sodium chloride (0.5 mg/ml) in drinking water for 7 days. Group C received only sodium chloride (0.5 mg/ml). Blood glucose (BG), glycosuria, ketonuria, body weight and insulinemia were determined. The age of onset of diabetes was significantly higher for groups V2, V3 compared to group C, (p < 0.05) and depends on the metavanadate concentration (V3 vs. V1, p=0.006). The incidence of diabetes was lower in the rats treated with metavanadate than in the control group, but this difference was not statistically significant. In diabetic rats, the BG at the onset was higher in group C than in groups V, p < 0.05. Insulinemia, at the onset of the treatment as well as immediately after its cessation showed a drop in the treatment groups, proportionally to the dosage of vanadium, but later increased slowly and continuously until the end of the experiment. In conclusion, metavanadate delays the development of diabetes in BB-DP rats, but does not prevent its onset. A milder form of diabetes occurs in diabetic rats treated with metavanadate. The effects depend on the metavanadate concentration and 0.2 mg/ml is preferable.     

Effects of dietary phytase on body weight gain, body composition and bone strength in growing rats fed a low-zinc diet

Phytic acid, a major phosphorous storage compound found in foodstuffs, is known to form insoluble complexes with nutritionally essential minerals, including zinc (Zn). Phytases are enzymes that catalyze the removal of these minerals from phytic acid, improving their bioavailability. The objective of the present study was to determine the ability of dietary phytase to affect body weight, body composition, and bone strength in growing rats fed a high phytic acid, low Zn diet. Rats (n = 20) were fed either a control (AIN-93) or phytase supplemented (Natuphos, BASF, 1,500 phytase units (FTU)/kg) diet for a period of 8 weeks. Phytase supplementation resulted in increased (P<.05) bone and plasma Zn, but no change in plasma inorganic phosphorous or bone levels of Ca, Fe, or Mg. The addition of phytase to the diets resulted in a 22.4% increase (P<.05) in body weight at the end of the study as compared with rats fed a control diet. Dual x-ray absorptiometry (DXA) revealed that phytase supplementation resulted in increase lean body mass (LBM, P<.001) and increased bone mineral content (BMC, P<.001) as compared with feeding the control diet. Bone studies indicated that femurs and tibias from phytase supplemented rats had greater mass (P<.05) and were stronger (P<.05) than rats fed the control diet. This data suggest that the addition of phytase to low Zn diets results in improved Zn status, which may be responsible for beneficial effects on growth, body composition, and bone strength.     

Short term effects on bone quality associated with consumption of soy protein isolate and other dietary protein sources in rapidly growing female rats

Beneficial effects of soy protein consumption on bone quality have been reported. The effects of other dietary protein sources such as whey protein hydrolysate (WPH) and rice protein isolate (RPI) on bone growth have been less well examined. The current study compared effects of feeding soy protein isolate (SPI), WPH and RPI for 14 d on tibial bone mineral density (BMD) and bone mineral content (BMC) in intact and ovariectomized (OVX) rapidly growing female rats relative to animals fed casein (CAS). The effects of estrogenic status on responses to SPI were also explored. Tibial peripheral quantitative computerized tomography (pQCT) showed all three protein sources had positive effects on either BMD or BMC relative to CAS (P < 0.05), but SPI had greater effects in both intact and OVX female rats. SPI and E2 had positive effects on BMD and BMC in OVX rats (P < 0.05). However, trabecular BMD was lower in a SPI + E2 group compared to a CAS + E2 group. In OVX rats, SPI increased serum bone formation markers, and serum from SPI-fed rats stimulated osteoblastogenesis in ex vivo. SPI also suppressed the bone resorption marker RatLaps (P < 0.05). Both SPI and E2 increased alkaline phosphatase gene expression in bone, but only SPI decreased receptor activator of nuclear factor-kappaB ligand (RANKL) and estrogen receptor gene expression (P < 0.05). These data suggest beneficial bone effects of a soy diet in rapidly growing animals and the potential for early soy consumption to increase peak bone mass.     

The effect of dietary n-3 long-chain polyunsaturated fatty acids on femur mineral density and biomarkers of bone metabolism in healthy, diabetic and dietary-restricted growing rats

INTRODUCTION: Dietary fish oil promotes bone formation in healthy states, but its effect during insulin deficiency or nutrient restriction is unclear. METHODS: Eighty weanling male rats were randomized to receive an injection of streptozotocin to induce insulin deficiency (diabetes) or saline (control) and a diet containing soy oil or corn + fish oil for 35 days. Half of the saline-injected rats were randomized to 20% dietary restriction. Measurements were growth, biomarkers of bone metabolism and femur bone mass. RESULTS: Density of femur was elevated in the corn + fish group and reduced in the diabetes group. Plasma osteocalcin and bone prostaglandin E2 (PGE2) were reduced by the corn + fish diet. N-telopeptide, IGF-1, bone PGE2 and urinary Ca were highest and calcitriol lowest in the diabetes group. CONCLUSIONS: These data suggest that the benefit of a diet high in n-3 long-chain polyunsaturated fatty acid is most advantageous to long bone density in healthy states.     

Effect of different dietary proteins on plasma and liver fatty acid compositions in growing rats

The activities of key glutamine and urea cycle enzymes were assayed in liver homogenates from control and chronically acidotic rats and compared with citrulline and urea productions by isolated mitochondria and intact liver slices, respectively. Glutamine-dependent urea and citrulline synthesis were increased significantly in isolated mitochondria and in liver slices; the activities of carbamoyl phosphate synthetase and arginase were unchanged and increased, respectively. Glutamine was not a precursor in the carbamoyl phosphate synthetase system, suggesting that the glutamine effect is an indirect one and that glutamine requires prior hydrolysis. Increased mitochondrial citrulline synthesis was associated with enhanced oxygen consumption, suggesting glutamine acts both as a nitrogen and fuel source. Hepatic phosphate-dependent glutaminase was elevated by chronic acidosis. The results indicate that the acidosis-induced reduction in ureagenesis and reversal from glutamine uptake to release observed in vivo are not reflections of corresponding changes in the hepatic enzyme content. Rather, when available, glutamine readily supports ureagenesis, suggesting a close coupling of hepatic glutaminase flux with citrulline synthesis.     

Effect of dietary protein level and source on bone mineralization in rats

Bone mineralization was studied in rats. Animals were divided into three feeding groups: LCP - diet with 13.5% crude protein in DM (5% of gluten, 10% of casein), HCP - diet with 21.2% CP in DM (8% of gluten, 10% of casein), and LSM - diet based on grain meals and meat-bone meal (21% CP in DM). After 28 days feeding, animals were euthanased by cervical dislocation and femur bones were collected, weighed and kept frozen until analyses. Diets with 21% protein (HCP, LSM) significantly increased weight of femur bones. Despite of the substantially higher ash level (7.1%) in the LSM diet than in the LCP diet (3.4%), rats of both groups had the similar bone concentration of Ca (15.7 +/- 1.1 vs. 17.4 +/- 1.1 g/kg) and Zn (178.7 +/- 7.9 vs. 173.0 +/- 8.5 mg/kg). However bone density in LSM rats was significantly higher than in LCP ones. Although rats fed HCP diet had intermediate bone density, the bone concentration of Ca (11.4 +/- 0.5 g/kg) and Zn (145.1 +/- 2.9 mg/kg) was significantly lower, than in animals fed LCP and LSM diets. This was related to the very wide protein/calcium (37:1 g/g) and protein/zinc (5.3:1 g/mg) ratios in HCP diet. Those ratios were narrowest in the LSM diet: 16.2:1 (CP/Ca) and 2.6:1 (CP/Zn). It can be conluded that protein/mineral ratio in a diet is a very important factor in bone development, besides dietary protein and ash contents itselves.