Improving effect of feeding with a phosphorylated guar gum hydrolysate on calcium absorption impaired by ovariectomy in rats

We have previously reported that a phosphorylated guar gum hydrolysate (P-GGH) promoted calcium absorption and the accumulation of bone calcium in rats. We now investigate the effect of P-GGH (50 g/kg of diet) on the intestinal calcium absorption and bones of ovariectomized (OVX) rats in comparison with sham-operated rats over a six-week ingestion period. The apparent calcium absorption was decreased by aging and ovariectomy in the rats fed on the control and GGH diets (50 g/kg of diet), but not in the rats fed on the P-GGH diet. The absorption was higher in the P-GGH group than in the GGH and control diet groups in the fourth and sixth weeks after feeding the test diets to OVX rats. Femoral calcium and strength were decreased by OVX in the rats fed on the control and GGH diets, but not in the rats fed on the P-GGH diet. The values of these parameters were higher in the P-GGH group than in either the control or GGH group of OVX rats. The amount of soluble calcium in the ileal contents was higher in the P-GGH group than in the control and GGH groups. These results indicate that P-GGH may be useful for preventing the reduction of intestinal calcium absorption and bone in the condition of estrogen deficiency.     

Effect of a phosphorylated guar gum hydrolysate on increased calcium solubilization and the promotion of calcium absorption in rats

The effect of a phosphorylated guar gum hydrolysate (P-GGH) on calcium solubilization and its influence on calcium absorption were studied in vitro and in vivo. P-GGH was prepared by chemically modifying a guar gum hydrolysate (GGH) with sodium metaphosphate. P-GGH inhibited the precipitation of calcium phosphate in vitro. The apparent calcium absorption and the amount of femur calcium were significantly higher in rats fed on the P-GGH diet (50 g/kg of diet) than in rats fed on the GGH diet (50 g/kg of diet) or the control diet. Moreover, the amount of soluble calcium in the ileal contents was significantly higher in the P-GGH-fed rats than in the GGH-fed rats. These results indicate that P-GGH may inhibit calcium phosphate formation in the lower part of the small intestine, and thus increase calcium absorption.     

Ingestion of raffinose promotes calcium absorption in the large intestine of rats

We examined the effects of feeding raffinose on intestinal calcium absorption in ovariectomized rats by two separate experiments. In experiment 1, female Sprague-Dawley rats (6 wk old) were divided into two groups: sham operation and ovariectomy, and fed diets with or without raffinose (30 g/kg diet) for 4 wk. In experiment 2, ovariectomized rats with cecocolonectomy or transsection and reanastomosis (sham) were divided into two groups as in experiment 1 and fed the same diets for 3 wk. In experiment 1, calcium absorption was lower in the ovariectomized rats than in the sham rats but calcium absorption in rats fed the raffinose diet was higher than that in rats fed the raffinose-free diet. In experiment 2, increased calcium absorption in the raffinose group was abolished by cecocolonectomy. The impaired absorption in ovariectomized rats was restored by feeding raffinose. The large intestine is involved in the beneficial effects of raffinose.     

The effects of isomaltulose,isomalt, and isomaltulose-based oligomers on mineral absorption and retention

We carried out a balance study to examine the effects of isomaltulose, lactose, isomalt, and isomaltulose-based oligomers (IBOs) on mineral (calcium, magnesium, phosphorus, and iron) absorption and retention. Four-week-old male Wistar rats were divided into five groups of six rats each and fed a basal diet or diet the containing either 5% isomaltulose, 5% lactose, 5% isomalts or isomaltulose-based oligomers (IBOs) ad libitum for 16 d. After 1 wk, the animals were subjected to a 5-d mineral (calcium, magnesium, phosphorus, and iron) balance study. The isomalt feeding, as well as the IBOs feeding, led to significantly elevated mineral absorption and retention. On the other hand, lactose feeding, widely known to enhance calcium absorption, increased only calcium absorption and isomaltulose feeding did not affect mineral absorption or retention. The organic acids in cecum contents were increased by IBOs or isomalt feeding. Succinic and acetic acids in cecum contents were significantly increased by IBOs feeding. Similarly, succinic acetic, and i-valeric acids and total amount of organic acid in cecum content were significantly increased by isomalt feeding. Although the organic acids in cecum contents were increased by IBOs or isomalt feeding, the PH values and acidity in cecum contents were not changed by IBOs or isomalt feeding. The effect of addition of various organic acids to the mucosal fluid was examined with in vitro study using a hindgut segment. By the addition of acetic acid, and butyric acid, the mineral (calcium, magnesium, and phosphorus) uptake was increased.     

Effects of dietary calcium on the metabolism of trace elements in male and female rats

The effect of dietary calcium on the metabolism of iron, zinc, copper, and manganese in male and female rats was investigated. For 3 or 6 weeks the rats were fed three diets containing: (1) 0.26, (2) 0.52, or (3) 2.08% Ca. The apparent absorption of iron was depressed by the high calcium diet, and manganese absorption was highest in the low calcium groups. Generally there was a decrease in the absorption of minerals from 3 to 6 weeks. With an increase in the dietary calcium the absorption of Ca and P decreased. The liver iron concentration in the females fed diet 3 decreased from about 600 to 200 microg/g dry weight. The high calcium intake also caused a slight increase in the heart calcium levels in both sexes. However, diet 3 prevented kidney calcification in the female rats at 6 weeks and this was attributed to a dramatic decrease in the urinary phosphorus, although the calcium had increased about 40 times. In males, on the other hand, the high calcium diet caused some kidney calcification.     

Effects of vitamin K2 administration on calcium balance and bone mass in young rats fed normal or low calcium diet

OBJECTIVE: The purpose of this study was to examine the effects of vitamin K2 administration on calcium balance and bone mass in young rats fed a normal or low calcium diet. METHODS: Forty female Sprague-Dawley rats, 6 weeks of age, were randomized by stratified weight method into four groups with 10 rats in each group: 0.5% (normal) calcium diet, 0.1% (low) calcium diet, 0.5% calcium diet + vitamin K2 (menatetrenone, 30 mg/100 g chow diet), and 0.1% calcium diet + vitamin K2. After 10 weeks of feeding, serum calcium and calciotropic hormone levels were measured, and intestinal calcium absorption and renal calcium reabsorption were evaluated. Bone histomorphometric analyses were performed on cortical bone of the tibial shaft and cancellous bone of the proximal tibia. RESULTS: Feeding a low calcium diet induced hypocalcemia, increased serum parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D [1,25(OH)2D] levels with decreased serum 25-hydrovyvitamin D [25(OH)D] level, stimulated intestinal calcium absorption and renal calcium reabsorption, and reduced cortical bone mass as a result of decreased periosteal bone gain and enlarged marrow cavity, but did not significantly influence cancellous bone mass. Vitamin K2 administration in rats fed a low calcium diet stimulated renal calcium reabsorption, retarded the abnormal elevation of serum PTH level, increased cancellous bone mass, and retarded cortical bone loss, while vitamin K2 administration in rats fed a normal calcium diet stimulated intestinal calcium absorption by increasing serum 1,25(OH)2D level, and increased cortical bone mass. CONCLUSION: This study clearly shows the differential response of calcium balance and bone mass to vitamin K2 administration in rats fed a normal or low calcium diet.     

Alcohol-associated folate disturbances result in altered methylation of folate-regulating genes

Folate plays a critical role in maintaining normal metabolic, energy, differentiation and growth status of all mammalian cells. The steady-state accumulation of folate seems to depend on the activity of two enzymes: folylpolyglutamate synthetase (FPGS), which adds glutamate residues, and gamma-glutamyl hydrolase (GGH), which removes them, enabling it to be transported across the biological membranes. Overexpression of GGH and downregulation of FPGS would be expected to decrease intracellular folate in its polyglutamylated form, thereby increasing efflux of folate and its related molecules, which might lead to resistance to drugs or folate deficiency. The study was sought to delineate the activity of GGH and expression FPGS in tissues involved in folate homeostasis during alcoholism and the epigenetic regulation of these enzymes and transporters regulating intracellular folate levels. We determined the activity of GGH and expression of FPGS in tissues after 3 months of ethanol feeding to rats at 1 g/kg body weight/day. The results showed that there was not any significant change in the activity of folate hydrolyzing enzyme GGH in ethanol-fed rats while there was significant down regulation in the expression of FPGS. Ethanol feeding decreased the total as well as polyglutamated folate levels. There was tissue-specific hyper/hypo methylation of folate transporter genes viz. PCFT and RFC by chronic ethanol feeding. Moreover, hypermethylation of FPGS gene was observed in intestine and kidney without any change in methylation levels of GGH in the ethanol-fed rats. In conclusion, the initial deconjugation of polyglutamylated folate by GGH was not impaired in ethanol-fed rats while the conversion of monoglutamylated folate to polyglutamylated form might be impaired. There was tissue-specific altered methylation of folate transporter genes by chronic ethanol feeding.     

克山病病区粮喂养大鼠后心肌细胞自由钙浓度变化与硒的作用

为了解克山病的发病机理,本文研究了低硒对心肌细胞钙转运的影响。用克山病病区粮喂养的大白鼠与用非病区粮喂养的大白鼠相比,心肌细胞胞浆自由钙的浓度高,心肌细胞膜流动性及Na~+,K~+-ATP酶活性也高,在病区粮中添加适量的硒,上述指标与用非病区粮喂养的大白鼠的差距缩小,说明低硒是引起心肌细胞钙转运失常从而使细胞浆自由钙浓度升高的重要因素但不是唯一的因素,文中讨论了细胞浆自由钙浓度与细胞膜流动性、Na~+,K~+-ATP酶活性及心肌线粒体功能的关系,以及低硒对它们的影响。     

Effect of citrate feeding on free radical induced changes in experimental urolithiasis.

Feeding calculi producing diet (CPD) to rats for 4 weeks produced calcium oxaltate stones. Supplementation of sodium citrate to CPD (c-CPD) prevented stone formation. Except oxalate, the excretion of calcium, phosphorus and magnesium was restored to normal in c-CPD fed rats. The CPD fed rats exhibited increase in glycolic acid oxidase (GAO) and lactate dehydrogenase (LDH) activities and only GAO activity was partially restored in c-CPD fed rats. Kidney sub-cellular fractions of calculi producing diet (CPD) fed rats showed increased susceptibility for lipid peroxidation in presence of promotors. Antioxidant enzyme activities of superoxide dismutase (SOD), catalase and glutathione peroxidase and antioxidant concentrations of reduced glutathione, total thiols, ascorbic acid and vitamin E were significantly decreased while the xanthine oxidase activity, and concentrations of hydroxyl radical, diene conjugates and hydroperoxides were significantly increased in CPD fed rats. The susceptibility to lipid peroxidation, activities of antioxidant enzymes, and the concentration of antioxidants were not normalized by feeding citrate.     

Interactions between insulin and thyroid hormone in the control of lipogenesis.

1. The effects of intragastric glucose feeding and L-tri-iodothyronine (T3) administration on rates of hepatic and brown-fat lipogenesis in vivo were examined in fed and 48 h-starved rats. 2. T3 treatment increased hepatic lipogenesis in the fed but not the starved animals. Brown-fat lipogenesis was unaffected or slightly decreased by T3 treatment of fed or starved rats. 3. Intragastric glucose feeding increased hepatic lipogenesis in control or T3-treated fed rats, but did not increase hepatic lipogenesis in starved control rats. Glucose feeding increased hepatic lipogenesis if the starved rats were treated with T3. Glucose feeding increased rates of brown-fat lipogenesis in all experimental groups. The effects of glucose feeding on liver and brown-fat lipogenesis were mimicked by insulin injection. 4. The increase in hepatic lipogenesis in T3-treated 48 h-starved rats after intragastric glucose feeding was prevented by short-term insulin deficiency, but not by (-)-hydroxycitrate, an inhibitor of ATP citrate lyase. The increase in lipogenesis in brown adipose tissue in response to glucose feeding was inhibited by both short-term insulin deficiency and (-)-hydroxycitrate. 5. The results tend to preclude pyruvate kinase and acetyl-CoA carboxylase as the sites of interaction of insulin and T3 in the regulation of hepatic lipogenesis in 48 h-starved rats. Other potential sites of interaction are discussed.     

Effect of shellfish calcium on the apparent absorption of calcium and bone metabolism in ovariectomized rats

Fossil shellfish powder (FS) and Ezo giant scallop shell powder (EG) were rendered soluble with lactate and citrate under decompression (FSEx and EGEx, respectively) and we examined the effects of lactate-citrate solubilization of FS and EG on mineral absorption, tissue mineral contents, serum biochemical indices and bone mineral density (BMD) in ovariectomized (OVX) rats. The apparent absorption ratios of minerals tended to be high in the rats fed with the solubilized mineral sources, those in the FSEx group being significantly higher than in the FS group. There was no significant difference in the tibia mineral content among the OVX groups. BMD at the distal femoral diaphysis was significantly increased by FSEx and EGEx feeding. It is suggested that solubilization with lactate and citrate under decompression increased the solubility and bioavailability of calcium from such natural sources of shellfish calcium as FS and EG.     

Sterol balance studies in the rat. Effects of dietary cholesterol and beta-sitosterol on sterol balance and rate-limiting enzymes of sterol metabolism.

Sterol balance measurements using isotopic and chromatographic techniques were carried out in rats fed diets containing beta-sitosterol (0.8%) and cholesterol (1.2%). The activities of the rate-limiting enzymes of cholesterol synthesis (beta-hydroxy-beta-methylglutaryl-CoA reductase, EC 1.1.1.34) and bile acid synthesis (cholesterol 7 alpha-hydroxylase) were determined in the same animals. Cholesterol feeding increased cholesterol absorption from 1.2 to 70 mg/day. The increased absorption was compensated for by inhibition of hepatic cholesterol synthesis, enhanced conversion of cholesterol to bile acids (from 13.7 to 27.3 mg/day) and a slight increase in the excretion of endogenous neutral steroids (from 7.7 to 11.2 mg/day). Despite the adaptation there was accumulation of cholesterol in the liver (from 2.2 to 9.2 mg/g). Beta-Sitosterol feeding inhibited cholesterol absorption (calculated absorption was zero). In these rats there was enhanced cholesterol synthesis (from 20.0 to 28.8 mg/day, but no change in the rates of bile acid formation. Measurements of the activities of the rate-limiting enzymes showed fair correlation with cholesterol-bile acid balance. In cholesterol fed animals, beta-hydroxy-beta-methylglutaryl-CoA reductase was inhibited 80% and cholesterol 7 alpha-hydroxylase was enhanced 61%. In beta-sitosterol-fed animals, the reductase was increased 2-fold and cholesterol 7 alpha-hydroxylase was not significantly different from controls.     

Diet-induced adaptation of intestinal fructose absorption in the rat.

The effect of dietary sucrose, fructose and glucose on the intestinal absorption of fructose and glucose was investigated in adult rats in vivo: Glucose absorption was not affected by the type of dietary carbohydrate, while the absorption of fructose was increased by the ingestion of the sucrose or fructose diet, as compared with the glucose diet. An almost maximal increase of fructose absorption was already observed when the quarter of the total dietary carbohydrates was replaced by fructose. Faecal fructose elimination declined during the feeding experiment. The enhanced intestinal absorption of the fructose load in rats fed the fructose diet was manifested by higher concentrations of fructose, but also of glucose and lactate in the hepatic portal blood.     

High P diet induces acute secretion of parathyroidhormone without alteration of serum calcium levels in rats

To find whether a high phosphorus (P) diet stimulate the secretion of PTH, a high-P diet was fed to rats and an increase in serum P levels has occurred. All rats were fed a control diet (0.5% calcium (Ca), 0.5% P) for 7 days, while they were being adapted, for 1 hour at 8:00 AM and again at 8:00 PM. Four groups were switched to the high-P diet (0.5% Ca, 1.5% P) at the time of their morning meal for 1 hour. The other 4 groups continued to receive the control diet. Blood samples were collected from the rats in the remaining group, which served as a pre-feeding control. Every 30 minutes after the start of feeding (30, 60, 90, 120 min), blood samples were collected from the rats in the groups fed the control and high-P diets. Serum P concentrations increased upon intake of the high P diet, within 30 minutes after the start of feeding. Serum PTH levels also increased upon intake of the high P diet, within 30 minutes after the start of feeding, and the levels were significantly higher in the high-P group than in the control group. However, no significant difference was observed in serum Ca levels between the two groups. From these results, our findings suggest that an increase in serum P concentration might be a trigger of PTH secretion without any changes of serum calcium levels.     

Enhancing effect of dietary vinegar on the intestinal absorption of calcium in ovariectomized rats.

We studied the effect of dietary vinegar on calcium absorption by using ovariectomized rats fed on a low-calcium diet. The apparent absorption of calcium was higher when the rats were fed on a diet containing 1.6% vinegar for 32 days than when fed on a diet without vinegar (P < 0.05). The calcium content in the femur of the rats given diets containing 0.4% and 1.6% vinegar were also higher (P < 0.05). The serum parathyroid hormone level was lower and the crypt depth of the duodenum thicker in the rats fed on a diet containing 1.6% vinegar (P < 0.05). These results suggest that dietary vinegar enhanced intestinal calcium absorption by improving calcium solubility and by the trophic effect of the acetic acid contained in vinegar, which would reduce the bone turnover caused by ovariectomy and be helpful in preventing osteoporosis.     

Acute versus chronic effects of whey proteins on calcium absorption in growing rats

The acute and chronic effects of whey proteins on calcium metabolism and bone were evaluated. In acute studies, 8-week-old male rats were gavaged with 50 mg whey protein concentrate (WPC) and 25 mg calcium. 45Ca was administered intravenously or orally. Kinetic studies were performed, and femurs were harvested. Four of seven WPCs significantly increased femur uptake of 45Ca compared with controls. One WPC at 50 mg enhanced calcium absorption over a range of calcium intakes from 35.1 +/- 9.4% to 42.4 +/- 14.0% (P < 0.01). Three of the most effective WPCs were tested further in a chronic feeding study. One hundred 3-week-old rats were randomly divided into four adequate dietary calcium (ADC; 0.4% Ca) groups (control of 20% casein and three WPC groups with 1% substitution of casein with each of three WPCs) and two low calcium (LC; 0.2% Ca) groups (control of 20% casein and one WPC group with 1% substitution of casein with one WPC). After 8 weeks, there was no effect of WPCs on femur uptake of 45Ca among ADC groups and there was no effect of WPCs on calcium retention, femur breaking force, femur bone mineral density, or total femur calcium at either dietary calcium intake. However, whole body bone mineral content (BMC) was significantly higher (P < 0.05) in the three whey protein concentrate ADC groups compared with the ADC control group. Total BMC at the proximal tibia in whey protein ADC groups was increased, as shown by peripheral quantitative computed tomography. Our results indicate that the acute calcium absorption-enhancing effect of whey proteins did not persist through long-term feeding in rats. However, the initial enhancement of calcium absorption by whey protein was sufficient to increase BMC.     

Effects of Dietary Nasunin on the Serum Cholesterol Level in Rats

The effects of nasunin, a major anthocyanin in eggplant, and its aglycone, delphinidin, on the serum cholesterol conpentration were determined in rats fed with a cholesterol-enriched diet. The serum total cholesterol and HDL-cholesterol concentrations tended to be decreased and increased, respectively, by feeding nasunin and delphinidin, while the fecal excretion of both cholesterol and bile acids tended to be increased by feeding with the anthocyanins. There was no difference between the nasunin and delphinidin activity to decrease serum total cholesterol, nor to increase serum HDL-cholesterol or the fecal excretion of cholesterol and bile acids. These results suggest that the slightly lower serum total cholesterol concentration in rats fed with nasunin and delphinidin may in part be due to inhibition of the intestinal absorption of both cholesterol and bile acids by these anthocyanins, and that the delphinidin moiety of nasunin mainly contributes to this activity.     

Effects of DFA IV in rats: calcium absorption and metabolism of DFA IV by intestinal microorganisms.

Di-D-fructose-2,6':6,2'-dianhydride (DFA IV) is a disaccharide consisting of two fructose residues that can be prepared from levan by levan fructotransferase from Arthrobacter nicotinovorans GS-9, and it can be expected to have novel physiological functions from its unique structure. In this study, the effects of DFA IV on calcium absorption and the metabolism of DFA IV by intestinal microorganisms were studied in rats to examine the physiological functions of DFA IV. The apparent calcium absorption in rats fed with DFA IV was significantly higher than that in the control rats, and it seems that calcium absorption had almost been completed at the end of the small intestine. DFA IV also increased the calcium absorption in in vitro experiments, using everted jejunal and ileal sacs, and this result supports the finding obtained in the in vivo experiments. These results indicate that DFA IV may have a function for increasing the calcium absorption in the small intestine of rats. However, the effect in the large intestine could not be clearly observed because of the lack of calcium that reached there. The results of analyses of organic acids in the cecal and colonic contents and of DFA IV in the fecal, cecal, and colonic contents showed that the metabolism of DFA IV by microorganisms in the large intestine progressed gradually, and that DFA IV was converted mainly to acetate, butyrate, and lactate.     

The amount and distribution of water, dry matter, and sugars in the digestive tract of rats fed xanthan gum

Diets containing a nutritionally adequate, high-maltose nutrient mixture and either 4% xanthan gum or 4% cellulose were fed ad libitum to rats. The feeding of this gum increased the combined weight of the small intestine and its contents by 110%. This effect was partially due to an enlarged intestinal cell mass and to extra dry matter in the contents but chiefly to a 400% increase in intraluminal water. Xanthan feeding enhanced greatly the persistence of sugars beyond the proximal quarter of the small intestine and increased their total recovery in the first three quarters of that organ by 150%. The xanthan-induced increase in intraluminal water in the small intestine was partially due to a slowed absorption of osmotically active substances from the gut.     

Effects of vitamin D supplementation on calcium balance and bone growth in young rats fed normal or low calcium diet

OBJECTIVE: We examined the effect of vitamin D supplementation on bone growth in young rats fed a normal or low calcium diet. METHODS: Fifty female Sprague-Dawley rats, 6 weeks of age, were randomized by stratified weight method into five groups with 10 rats in each group: baseline control, 0.5% (normal) or 0.1% (low) calcium diet, and 0.5 or 0.1% calcium diet + vitamin D (25 microg/100 g, food intake). Duration of the experiment was 10 weeks. RESULTS: Vitamin D supplementation stimulated intestinal calcium absorption and increased urinary calcium excretion in rats fed a low or normal calcium diet. Vitamin D supplementation prevented the reduction in periosteal bone gain but enhanced enlargement of the marrow cavity and reduced the maturation-related cancellous bone gain in rats fed a low calcium diet, and increased the maturation-related cancellous and cortical bone gains in rats fed a normal calcium diet. CONCLUSION: This study shows the differential effects of vitamin D supplementation on born growth in young rats fed a normal or low calcium diet.