Bhagwan G. Shah

Factors affecting nephrocalcinosis in male and female rats fed AIN-76 salt mixture*

Abstract For the further investigation of nephrocalcinosis (NC) observed by us in male and female Sprague-Dawley rats fed purified diets (1), three experiments were conducted. In the first experiment the effect of the level of dietary protein on NC was investigated. Twenty male and 20 female weanling Sprague-Dawley rats were randomly divided (each sex separately) into 2 groups One group of each sex was fed, for 6 weeks, a purified diet containing 10% protein from casein and the other a diet containing 15% protein from the same source. The diets contained the AIN-76A vitamin and mineral mixtures. At the end of the experiment the kidneys of the rats in the 10% protein group contained (mg Ca/g dry weight, mean, minimum, maximum): male, 15.6, 0.3, 69.9; female, 49.0, 30.2, 69.1. The corresponding values for the animals in the 15% group were: male, 1.3, 0.2, 7.2; female, 24.0, 8.2, 48.4. Thus, the increase in the protein content of the diet decreased the kidney calcium levels. In the second experiment, three diets containing 20% protein from casein and 25 mg fluoride/kg with increasing levels of magnesium (0.10, 0.20, 0.27%) were tested in groups (10 each) of male and female weanling rats fed for 6 weeks. At the end, the calcium contents of the kidneys, expressed as above, were, for the diet with 0.10% Mg — male, 0.33, 0.29, 0.36; female, 0.98, 0.26, 6.22; and for the diet with 0.20% Mg — male, 0.30, 0.27, 0.34; female, 0.57, 0.29, 1.20; and for the diet with 0.27% Mg — male, 0.31, 0.29, 0.37; female, 0.54, 0.27, 1.07. These results indicated that a supplement of 25 mg fluoride/kg and a total magnesium content of 0.10% was sufficient to prevent NC in male rats but females fed the same level of fluoride and even 0.27% magnesium had kidney calcium levels somewhat higher than normal. The calcium, phosphorus and magnesium concentrations of the hearts in these animals were not affected. In the third experiment soy assay protein (SAP) was used at a 20% protein level with and without a supplement of 50 mg fluoride/kg and 0.22% magnesium (total 0.27%). Kidney minerals, urinary levels of minerals, creatinine and citrate were determined. Kidney calcium levels were somewhat lower than comparable casein-fed rats and the supplement prevented NC. The composition of urine indicated that females excreted more sulphate and calcium per g creatinine than males. This could explain the more severe NC found in female rats. The supplement caused an increase in the excretion of magnesium and citrate and a decrease in the urinary phosphorus level. These changes prevented NC in both male and female rats.

Effect of dietary cereal brans on the metabolism of calcium, phosphorous and magnesium in a long term rat study

Abstract The effect of cereal brans on the mineral metabolism of rats was studied in a seven month long experiment. Seven groups (10 each) of male and female Sprague-Dawley weanling rats were fed ad lib for 7 weeks, diets containing cellulose, oat bran, hard red spring wheat bran, soft white wheat bran, corn bran and rodent lab chow at 4% or 14% total dietary fibre. In the seventh week (Phase 1) a mineral balance study was conducted on five randomly selected rats from each group. During week 8 these animals were killed and liver, heart, muscle and femur collected from each animal. The remaining animals were continued on the same diets for 21 more weeks. A second amineral balance study was carried out during week 24 (Phase 2) and the animals were killed during week 29 after colonic function tests during weeks 25–28. The diet, urine, feces and tissues were analysed for calcium, phosphorus, magnesium, phytate (in diet and feces only) and trace elements. Results on macro-mineral elements indicated that the fractional absorption of calcium, phosphorus and magnesium by male and female rats was not significantly different (P≤0.01). Absorption was affected by the level of the total mineral in the diet and not by the kind of fibre source. Variation in the digestibility of phytate was probably caused by the phytase activity in the bran rather than its phytate content. Digestibility during week 24 was less than during week 7 in most cases. The diets did not appreciably affect mineral levels in soft tissues and bone except the females in all purified diet groups showed severe nephrocalcinosis in both phases. Kidneys of males fed some diets showed mild calcification in phase 2. The absence of nephrocalcinosis in females fed the rat chow was associated with low levels of urinary phosphorus and also to the fluoride and high magnesium content of the chow.

Prevention of nephrocal cinosis in male and female rats by providing fluoride and additional magnesium in the diet

Nephrocalcinosis (NC) was observed in young Charles River (CD) Sprague Dawley rats fed for six weeks a purified diet containing 20% protein from casein and 3% Bernhart-Tomarelli (11) or 3.5% AIN-76 (12) salt mixtures, but not in rats fed a stock diet which contained 0.54% Cl, 0.27% Mg and 40 mg/kg F. Females were more susceptible than males. The addition of 50 mg fluoride (as sodium fluoride) per kg prevented NC in all the males (kidney Ca, mg/g dry weight: median, 0.40; range, 0.30–0.46) but not in all the females (0.49, 0.25–1.86), the corresponding figures for stock diet fed rats being: male; 0.26, 0.25–0.28; female; 0.34, 0.28–0.58. Doubling the level of fluoride did not reduce NC further. Increasing the dietary level of chloride to 0.54% (equal to that in the stock diet) in the presence of 50 mg/kg fluoride resulted in kidney calcium levels which were not significantly different from those in female rats fed fluoride alone. Nephrocalcinosis was prevented in both males and females when the diet contained levels of chloride and magnesium equal to those in the stock diet and 50 mg/kg fluoride, irrespective of whether Bernhart-Tomarelli or AIN-76 salt mixture was added to the diet. Magnesium added at 0.27% level with 50 mg/kg fluoride also was equally effective in preventing kidney calcification. Any dietary change did not have any significant effect on liver or heart calcium level.

Sodium and potassium content of the Canadian diet

Abstract On the basis of the food consumption data obtained in the Canadian Nutrition Survey, representative food samples were collected in Vancouver, Winnipeg, Montreal and Halifax during summer and winter. After preparing the foods in a normal way, but without adding salt, ten food group composites were prepared. They were analysed for sodium and potassium. The total diet was found to contain 1142 mg sodium and 1194 mg potassium per 1000 kcal. The sodium included that added by the food manufacturing industry to about one-quarter of the 120 food items included in the diet. About 70 percent of the sodium and 50 percent of the potassium were provided by three major food groups viz. milk and dairy products; meat, fish and poultry; cereals and cereal products. Fruit products, vegetables, potatoes and mixed dishes supplied 9–16 percent of the potassium. Vegetables and mixed dishes contained about 10 percent of the sodium. The amounts of potassium in the diets of various physiological groups, including pregnant women, were more than the Canadian recommendations. The sodium intakes were 2 to 5 times the recommended amounts.

Different dietary calcium levels required to prevent nephrocalcinosis in male and female rats

Abstract The effect of a dietary CaP weight ratio of 1.3 to 3.0 on nephrocalcinosis was investigated in male and female weanling Sprague-Dawley rats fed the AIN-76 salt mixture for 6 weeks. The diet containing 0.8% Ca (CaP=2) prevented kidney calcification in male rats but the females required 1.2% Ca (CaP=3). However, at this dietary calcium level some of the males had an above normal kidney calcium content. In the case of the male and female animals that were fed the 1.2% Ca diet, the urine samples collected during the last week contained the lowest amount of phosphorus, but the calcium excreted by the males increased about 50 times that by other animals, whereas the corresponding increase for females was at the most 5 times. Thus the dietary calcium required for the prevention of nephrocalcinosis varied according to sex. It is suggested that the phosphorus content of the AIN-76 salt mixture be reduced to 0.3% and an optimal combination of Ca, Mg and if necessary fluoride be determined.

The lack of effect of synthetic phosphoseryl peptide on calcium absorption by the rat

Abstract The purpose of this experiment was to test in vivo the effect on calcium absorption of synthetic phosphoseryl peptide (SPP), which occurs in bovine casein. Twenty-one male weanling Sprague-Dawley rats were randomly divided into 3 equal groups and fed 3 diets for 4 weeks: diet 1, SAP (soy assay protein), diet 2, SAP+SPP and diet 3, NFDM (non-fat dry milk powder). All diets contained 0.3% Ca and 0.4% P, the source of calcium in diets 1 and 2 being CaCO 3 and milk powder in diet 3. During the last week the apparent absorption of calcium was determined. At the end, the right femur was taken from each animal. Diets, feces and femurs were analysed for calcium, phosphorus, magnesium and manganese. The addition of SPP did not have any effect on calcium absorption from the SAP diet. Apparent calcium absorption from the NFDM diet (96%) was significantly higher than that from the SAP diets (84, 87%) but there was no difference in femur calcium. The tested compound [Ser (P)] 3 -Glu (SPP) did not have any effect on the absorption or on the femur content of phosphorus, magnesium or manganese. The results of this study point out the need for confirming the results of intestinal loop studies by an in vivo experiment.

Estimated mineral nutrients in a representative Canadian diet

Abstract The calcium, phosphorus, magnesium, iron, zinc, copper and managenese content of a representative Canadian diet was determined by analysing 11 different food group composites. The amounts of food included in the diet were based on the Nutrition Canada Food Consumption Patterns Report. The minerals in the diet were (mg/1000 kcal): Ca, 380; P, 567; Mg, 107; Fe, 4.5; Zn, 5.2; Cu, 0.49; Mn, 0.82. The proportion of the minerals, except calcium, provided by the diet groups was correlated with the energy contribution of each group. With the exception of some adults over 50 y, the content of minerals per 1000 kcal of the diet would be sufficient to meet the recently recommended intakes in Canada.

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.

BIOAVAILABILITY OF IRON IN GROUND BEEF AND PLANT PROTEIN CONCENTRATES

Abstract Weanling male Wistar rats were fed a low iron basal diet for 4 weeks. They were then divided into 16 groups according to a randomized block design based on hemoglobin level. During the repletion period of 2 weeks, one group was fed the basal diet. The other fifteen groups received ferrous sulphate, freeze-dried ground beef, ground granular soy product, a 2:1 mixture of beef and the soy product, or rapeseed protein concentrate as iron sources at three levels. All diets were isocaloric and isonitrogenous. The efficiency of iron utilization was calculated on the basis of iron gained in hemoglobin and iron consumed, applying appropriate correction for iron obtained from the ingredients of the basal diet. The relative biological value (RBV) of iron in the test source was calculated as the ratio between the efficiency for the test and the standard source (ferrous sulphate). The RBVs were: freeze-dried ground beef, 0.53; ground soy product, 0.62; 2:1 mixture of beef and soy product, 0.71; rapeseed protein concentrate, 0.55. The low availability of iron in beef containing 60% heme iron indicated that the anemic rat is not a suitable model for normal man, since the absorption of heme iron by man is much higher than that of inorganic or non-heme iron.

Lead concentration in the livers of Canadians

SummaryLiver specimens were collected at 114 (83 males and 31 females) autopsies on accident victims and on 4 stillborn infants in seven Canadian Cities. The age of the individuals ranged from newborn to 89 years with about 70% being 19–65 years. The level of lead in the samples was determined by atomic absorption spectroscopy using a carbon rod atomizer. The concentration of lead in liver was low (μg/g: Mean, 0.37, Median 0.28) at birth and during infancy. In the stillborn infants it ranged from 0.30 to 0.77 (Mean 0.51). Male adults had an average level of 1.78 (Median 1.41) whereas in adult females the corresponding values were 0.65 and 0.57. The liver lead concentration peaked at about the end of the fourth decade in adult males. There was no indication of any regional differences.