Low Calcium Group Research Articles

Effect of environmental calcium levels on calcium uptake in tilapia larvae Oreochromis mossambicus

Effects of environmental calcium concentrations on the survival, growth, body calcium content and calcium uptake kinetics in developing tilapia (Oreochromis mossambicus) larvae were studied. Fertilized eggs were incubated in high- and low-calcium artificial freshwater (0.88-0.96 mmol l(-1) vs. 0.02-0.03 mmol l(-1) CaCl2 or CaSO4) until 3 days after hatching. Tilapia larvae showed similar hatching rates and wet weights in either high- or low-calcium medium, indicating neither the development nor the growth in tilapia larvae was affected by the environmental calcium levels. The body calcium content in low-calcium groups was about 90-95% that of high-calcium groups, No matter what calcium source was used (CaCl2 or CaSO4), acclimation to low calcium medium caused a stimulation of calcium uptake (measured in 0.2 mmol l(-1) calcium),i.e., 1.2-1.3 fold higher than that of high calcium groups. This enhanced calcium uptake capacity was characterized by a 50% decrease in Km and a 25% increase in Jmax. Effect of different calcium salts on calcium influx was significant only in low calcium level,i.e., calcium influx in low-CaCl2 group higher than that in low-CaSO4 group. These results suggest that tilapia larvae are able to modulate their calcium uptake mechanism to maintain normal body calcium content and growth in environments with different levels of calcium.

Age-related functional changes of cancellous and cortical bone: histomorphometric study of bone in senescent rats fed with a low calcium diet

Age-related functional changes of bone is not well understood. The effect of aging on bone response to a low calcium feeding was studied using senescent rats. Male Wistar rats aged 23 to 28 months were fed either a low calcium diet (0.05% Ca, 0.35% P) or a normal calcium diet (0.5% Ca, 0.35% P) by using a pair feeding technique. They were sacrificed at intervals of 6, 9, and 20 days. Bone mineral density of the femur showed no changes in both cancellous and cortical bone in the low calcium group compared with the normal calcium group. The increment of osteoclast number was observed on day 6 in the cancellous bone of the tibia, but no significant changes were found during other periods. Mineralizing surface (MS/BS) and mineral appositional rate (MAR) were increased during the experimental period. On the other hand, cortical bone showed a transient increase of MS/BS on day 6, but other parameters revealed no changes during the experimental period. The magnitude of response was more evident in the cancellous bone than in the cortical bone. These results indicated that although responsiveness of remodeling activity to low calcium feeding is decreased in senescent rats, they are obvious in both the cancellous and cortical bone.

Dietary calcium reduces blood pressure, parathyroid hormone, and platelet cytosolic calcium responses in spontaneously hypertensive rats.

Dietary calcium effects on blood pressure, parathyroid hormone (PTH), and platelet cytosolic calcium concentrations were investigated. The dietary calcium (low, 0.2%; medium, 0.5%; and high, 2.0% wt/wt) was supplemented in spontaneously hypertensive rats from 6 through 22 weeks of age. Mean systolic blood pressure was decreased by age 12 weeks with calcium supplementation (low, 227 +/- 6 mm Hg; medium, 211 +/- 6 mm Hg; and high, 182 +/- 7 mm Hg; P < .001). By the 10th week of age, the low calcium group had significantly (P < .05) more elevated (44 +/- 2.3 pg/ml) plasma PTH compared with the high calcium-supplemented group (15 +/- 4.5 pg/mL). Regression analysis showed a significant (P < .001) positive correlation (r = 0.3) between systolic blood pressure and PTH. The platelet cytosolic calcium concentration was determined using the fura-2 method. The basal calcium was 134 +/- 5.5 nmol/L for the low calcium group and thrombin increased to 228 +/- 8 nmol/L (P < .0001; +70% change). The normal calcium group had 202 +/- 8 nmol/L; thrombin increased to 239 +/- 10 nmol/L (P < .0026; +19% change). The high calcium group had basal levels 145 +/- 7 nmol/L, with thrombin stimulating to 212 +/- 8 nmol/L (P < .0001; +46% change). Although thrombin increased platelet cytosolic calcium concentration in all groups, normal and high dietary calcium groups had smaller percentage increases (51% and 24% lesser, respectively) compared with the low dietary calcium group.(ABSTRACT TRUNCATED AT 250 WORDS)

Eicosapentaenoic acid inhibits bone loss due to ovariectomy in rats

Eicosapentaenoic acid (EPA), one of the polyunsaturated fatty acids, is well-known to have a wide variety of beneficial biological functions. In the present work we demonstrate another new beneficial effect of EPA on bone metabolism in vivo. Ovariectomized rats were divided into 4 groups under the same calorie intake condition; (1) normal diet, (2) low calcium diet (1.5mg/day), (3) EPA-enriched diet (160mg/day/kg), (4) EPA-enriched and low calcium diet. These diets were continued for 35 consecutive days. The bone weight of the femora and tibiae decreased significantly in the low calcium group, but the decrease was inhibited in the EPA-low calcium group. Moreover, in the rupture test, which indicates bone strength, the femora in the low calcium group were easier to break than in the normal calcium diet groups. In the EPA-low calcium group the strength of the bone was equivalent to that in the normal diet group. These results suggest that an EPA-enriched diet prevents the loss of bone weight and strength caused by oestrogen deficiency or inadequate nutrition. There is a possibility that EPA could be developed to be a novel anti-osteoporosis drug.

Comparative Effects of Calcium Deficiency and Supplements on the Intestinal Absorption of Zinc in Rats.

The purpose of this study was to clarify the influence of calcium on zinc status. The animals were divided into four groups consisting of five rats in each group. The control group was fed on basal diet with adequate levels of zinc and calcium while the experimental group was fed diets containing different levels of calcium ad libitum for 15 d. Low calcium did not significantly affect the zinc absorption percentage but there was a decrease in high and very high calcium groups. The retention percentage changes were found parallel to the changes in the absorption percentage curve. When the zinc distribution was expressed as per g of dry tissue, duodenum, brain, and liver zinc content increased in the low calcium group but a decrease in duodenum, ileum, and liver in the high and very high calcium groups was observed. Also the 65Zn amount in some tissues and blood increased substantially in the low calcium group, decreased in the high and very high calcium groups. These results suggest that calcium affects zinc status in rats.

Toxicity of vitamin D analogues in rats fed diets with standard or low calcium contents.

Sprague-Dawley rats were fed either a standard diet with 0.9/0.7% Ca/P or a semisynthetic low-calcium diet with 0.5/0.4% Ca/P and treated orally for 28 days with 1 alpha-hydroxycholecalciferol [1 alpha (OH)D3], a synthetic analogue of the physiologically active form of vitamin D3, 1 alpha,25-dihydroxycholecalciferol [1 alpha,25(OH)2D3], at dose levels of 0.2 and 2.0 micrograms kg/day. The high dose caused severe hypercalcaemia with retarded growth, nephrosis, and structural bone changes in rats fed the standard diet. The same dose caused only slight hypercalcaemia without growth retardation or bone changes, and only minimally affected the kidneys in rats fed the low-calcium diet. Hypercalcaemia with less pronounced pathological changes was found in the standard diet low-dose rats, whereas no hypercalcemia or pathological changes were found in the low-calcium diet low-dose group. The rats fed the low-calcium diet tolerated 1 alpha(OH)D3 at dose levels up to 10 times higher than rats on the standard diet. The use of diets low in calcium and low in phosphorus will thus allow the administration of higher dosages of vitamin D compounds without causing hypercalcaemia. This may permit a better evaluation of the pharmacologic and toxic effects not directly associated with the calcium-regulating properties of vitamin D metabolites and analogues.

Changes in protein kinase C activity in rat calvarial bone cells cultured in a low-calcium environment

This enzyme activity was examined in bone cells cultured for 8–10 days; the calcium concentration was 1.87 ± 0.05 ( n = 10) mM in the control medium and 0.34 ± 0.02 ( n = 10) mM in the low-calcium medium. The activity was significantly lower in the low-calcium group than in the control ( p < 0.01). The cytosolic fraction decreased more than the membranous fraction. After restoration to a regular calcium environment, the protein kinase C activity recovered rapidly to near the control value. The extent of recovery was greater in the membranous than in the cystolic fraction. These results suggest that the enzyme was inhibited in bone cells placed in a low-calcium environment, while the sensitivity in the membrane was enhanced.

Parathyroid hormone inhibits 25-hydroxyvitamin D3-24-hydroxylase mRNA expression stimulated by 1 alpha,25-dihydroxyvitamin D3 in rat kidney but not in intestine.

Using a cDNA probe for rat renal 24-hydroxylase, expression of its mRNA was compared in the rat kidney and intestine. Vitamin D-deficient rats received a single injection of 1 alpha,25-dihydroxyvitamin D3. Expression of 24-hydroxylase mRNA was first detected in the kidney at 3-h post-injection and increased thereafter. Similarly, 24-hydroxylase mRNA was expressed in the intestine after 1 alpha,25-dihydroxyvitamin D3 injection. However, the dose level of 1 alpha,25-dihydroxyvitamin D3 required to induce the intestinal 24-hydroxylase mRNA expression was only 1/100 the amount required to induce renal 24-hydroxylase mRNA. Induction of intestinal 24-hydroxylase mRNA expression by 1 alpha,25-dihydroxyvitamin D3 was far more rapid than that of renal 24-hydroxylase mRNA. Thyroparathyroidectomy shortened the time required to induce expression of renal, but not intestinal, 24-hydroxylase mRNA. Administration of either parathyroid hormone or cAMP to vitamin D-deficient rats greatly reduced the expression of 24-hydroxylase mRNA in the kidney but not in the intestine. When rats were fed a vitamin D-repleted diet containing 0.7% (adequate) or 0.03% (low) calcium for 2 weeks, intestinal expression of 24-hydroxylase mRNA could be induced only in the low calcium group. In contrast, renal mRNA expression was preferentially stimulated in the adequate calcium group. These results clearly demonstrate that the expression of 24-hydroxylase mRNA is down-regulated by parathyroid hormone in the kidney but not in the intestine.

Effect of low calcium on high-energy phosphates and sarcolemmal Na +/K +-ATPase in the infarcted-reperfused heart

This study was undertaken to compare the effect of low to normal serum calcium on biochemical parameters in the myocardium of dogs subjected to 90 min of coronary artery ligation followed by 30 min reperfusion. The accumulation of calcium, the decrease of adenosine triphosphate (ATP) and creatine phosphate (CP) and the inhibition of sarcolemmal ouabain-sensitive Na +/K +-ATPase which are prominent findings in the ischemic-reperfused myocardium, were studied under normal and low serum Ca produced by normal and modified hemodialysis (HD). The results showed a lower accumulation of Ca ( P < 0.002) in the ligated-reperfused myocardium of dogs subjected to low-calcium HD. In the same group of animals ATP was protected to some extent while CP was completely preserved. This may indicate that during reperfusion with low Ca, restored ATP is further utilized for CP regeneration. The activity of Na +/K +-ATPase was within normal values in the ligated-reperfused myocardium of the low-calcium group. The significantly ( P < 0.001) negative correlation between tissue calcium concentration and Na +/K +-ATPase activity under various conditions examined, provided additional evidence that low calcium is a protective factor of the enzyme activity during ischemia and reperfusion.

Calcium Metabolism in Great Dane Dogs Fed Diets with Various Calcium and Phosphorus Levels

The influence of dietary calcium on calcium metabolism was investigated in growing dogs that reach an adult body weight similar to that of humans. Seven groups of dogs (n greater than or equal to 5) were raised on a diet with a composition meeting the National Research Council (NRC) requirements (1974), but differing in calcium content, with or without a constant ratio to phosphorus. Control dogs fed 1.1% calcium and 0.9% phosphorus (all on a dry matter basis) were fed ad libitum (n = 10) or in restricted amounts (n = 6); dogs fed high calcium (3.3%) diets received either 0.9% phosphorus (n = 6) or 3.0% phosphorus (n = 6); dogs fed low calcium (0.55%) diets received either 0.9% phosphorus (n = 5 + 6) or 0.5% phosphorus (n = 8). Food intake, circulating total calcium and inorganic phosphorus concentrations and calcium metabolism, with 45Ca kinetics, were studied at 8, 14, 20 and 26 wk of age. Except for the difference in food intake in two groups at 14 wk (i.e., 0.55% calcium-0.9% phosphorus higher and 3.3% calcium-0.9% phosphorus lower, respectively, than the controls) no differences were noticed during the rest of the study. The mean plasma calcium concentrations did not differ between groups during the studies, whereas that of inorganic phosphorus revealed temporal aberrations in two groups. An absorption coefficient alpha of 45-66% was found for the control group. High and low calcium diets gave rise to values of 23-43% and 70-97%, respectively, for alpha irrespective of the phosphorus content of the diet.(ABSTRACT TRUNCATED AT 250 WORDS)

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 μg/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.

A histomorphometric analysis of the alveolar bone resorption process in calcium-deficient rats.

The present study was carried out to investigate the morphological changes in the alveolar bone in rats fed a low calcium diet, in order to establish an experimental model of alveolar bone resorption. Male Wistar rats (70-85 g in body weight) were either fed a low calcium diet (0.05% Ca, 0.35% P) or a control diet (0.5% Ca, 0.35% P) by using a pair feeding technique. The rats were sacrificed at intervals of 3, 6, 9 and 20 days. No difference was found in the growth rate between the control and the low calcium group. In the low calcium group, the bone area significantly reduced at day 3 and progressively decreased to 46% of that of the controls by the end of the experiment. The bone resorption was obvious in the cancellous bone during the early period of the experiment and then the cortical bone was seen to resorb. However, the contour of bone and the rate of bone apposition did not change. At day 20, bone still remained in three regions: the alveolar bone proper that surrounds the tooth sockets, a few cancellous bones and a thin wall-like cortical bone. These results suggest that the process of alveolar bone resorption is related to the mechanical forces induced by the occlusal function of the tooth and, further, that this experimental model might be useful for investigating the mechanism of alveolar bone resorption and disorders of the alveolar bone.

The calcium ionophore A23187 is a potent stimulator of the vitamin D3-25 hydroxylase in hepatocytes isolated from normocalcaemic vitamin D-depleted rats

The role played by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] and/or by calcium on the C-25 hydroxylation of vitamin D3 (D3) was studied in hepatocytes isolated from D-depleted rats which were divided into four treatment groups: Group 1 served as controls, Group 2 received calcium gluconate, Groups 3 and 4 were infused with 1,25(OH)2D3 at 7 and 65 pmol/24 h x 7 days respectively. The treatments normalized serum calcium in all but the controls which remained hypocalcaemic, while serum 1,25(OH)2D3 remained low in Groups 1 and 2 but increased to physiologic and supraphysiologic levels in Groups 3 and 4. The data show that basal D3-25 hydroxylase activities were not significantly affected by any of the treatments. Addition of CaCl2, EGTA, or Quin-2 in vitro revealed that relative to basal values, EGTA strongly inhibited the enzyme activity in all groups (P less than 0.0001), except in G 1; Quin-2 and CaCl2 had no significant effect on the activity of the enzyme in any of the groups. Addition of 1,25(OH)2D3 or A23187 in vitro in the presence of CaCl2 revealed that 1,25(OH)2D3 did not significantly affect enzyme activity, while A23187 was found to stimulate its activity in vitamin D-depleted animals, but most specifically in Group 2 (P less than 0.001); low serum calcium (Group 1) dampened (P less than 0.01), and 1,25(OH)2D3 treatment in vivo totally blunted (P less than 0.001) the response to A23187. The data suggest that 1,25(OH)2D3 supplementation in vivo has per se little or no effect on the basal D3-25 hydroxylase activity. The data show, however, that the magnitude of the response to various challenges in vitro is greatly influenced by the conditioning in vivo of the animals. They also show that A23187 can be a potent stimulator of the enzyme activity, which allowed us to demonstrate a significant reserve for the C-25 hydroxylation of D3 which is well expressed in hepatocytes obtained from D-depleted calcium-supplemented rats.

The effect of dietary sodium on urinary calcium and potassium excretion in normotensive men with different calcium intakes

On the basis of their usual calcium intake, 12 healthy normotensive male students were divided into a low and a high calcium group. Both groups were provided with complete diets containing the same calculated quantities, expressed per MJ, of protein, fat, carbohydrate, sodium, potassium, phosphorus, and calcium. After an initial period of two weeks during which all participants received an additional 100 mmol sodium daily, 6 participants received an additional 22 mmol sodium/day (low sodium), the other 6 participants 178 mmol sodium/day (high sodium). After two weeks the sodium regimes were crossed over for a subsequent two-week period. When the second week of the low sodium period is compared with the second week of the high sodium period, the increase in the calcium/creatinine ratio, expressed on molar basis, was 0.059 for the low and 0.053 for the high calcium group (p less than 0.05). The increase in the molar potassium/creatinine ratio was 0.65 for the low and 0.03 for the high calcium group (p less than 0.025). However, after correcting for the calcium intake the effect in the low calcium group was found to be greater (p less than 0.05). Sodium supplementation was found to have no effect on blood pressure, but mean systolic (p less than 0.10) and diastolic in the high calcium group were lower. This suggests that calcium may well play a role in the regulation of blood pressure.

Performance of Broiler Breeder Hens on Wire and Litter Floors

Two experiments were conducted with broiler breeder hens to study the influence of litter versus wire floor on weight and specific gravity of eggs. In Experiment 1, one group of broiler breeder hens was maintained on litter and the other on wire. Specific gravity was significantly higher for eggs from hens kept on litter floors. When hens on wire floors had access to litter in a feeder, an increase in egg specific gravity was noted within one day.In Experiment 2, broiler breeder hens, 52 weeks of age, were separated into three treatments: litter floor, wire floor, and wire floor with old litter material in feeder. When hens received 3.22% dietary calcium, the egg specific gravity was highest (P<.05) from hens on the litter floor, intermediate from hens on wire with access to litter, and lowest from hens on wire without access to litter. Hens on wire with access to litter consumed 18.3 g litter/bird/day, corresponding to an additional intake of 352 mg calcium and 93 mg phosphorus. They also received 4700 mg calcium and 790 mg phosphorus from the feed.The specific gravity of eggs from hens with access to litter was higher than for eggs from those hens without access to the litter when hens received diets with 1.0 and .15% calcium. No significant differences were found in egg weight among treatments. The hens on wire with access to litter and fed 1.0 or .25 or 3.22% dietary calcium consumed 24.5, 28.5, and 18.9 g more of litter, respectively. This resulted in additional intakes of 530 mg calcium, 140 mg phosphorus and 455 mg calcium, 120 mg phosphorus for the low calcium groups, respectively. They also consumed 790 mg phosphorus and 1.46 and .39 g calcium, respectively, from the feed. The additional minerals from the litter were responsible for the improved egg shells.

Metabolism of 109Cd in rats fed normal and low-calcium diets.

Growing male rats were fed purified diets that contained either 0.6% or 0.1% calcium to investigate the relationship of calcium intake to the uptake, tissue distribution, and excretion of 109Cd. An equal number of rats were fed either the 0.6 or 0.1% calcium diets for 4 wk before they were used for experiments. In the first experiment 11 rats from each dietary group were administered 5 muCi 109Cd by stomach tube and were then maintained in metabolism cages for 72 hr. Animals fed the low-calcium diet took up more 109Cd, as significantly higher levels of radioactivity were found in the intestinal mucosa, serum, lungs, liver, kidneys, and urine and a significantly lower level was found in the feces. Higher levels of 109Cd, associated with low-molecular-weight proteins that may be related to the absorption process, were found in the intestinal mucosa of the low-calcium group. In the second experiment 10 rats from each dietary group were administered 5 muCi 109Cd by subcutaneous injection and then maintained in a metabolism cage for 72 hr. No significant differences were found in the distribution or excretion of 109Cd except for the lungs where radioactivity was greater in the low-calcium group. The results of the study indicate that the enhanced cadmium toxicity observed in calcium-deficient animals exposed to the heavy metal is the result of an increased uptake from the small intestine.

The effects of fluoride and low calcium on the physical properties of the rat femur.

AbstractThe effect of fluoride on the physical properties of bone was investigated with the aid of an Instron materials tester. Two groups of weanling female rats, one on an adequate (0.6%) calcium diet and the other on a low (0.1%) diet were given the following dosage levels of fluoride (as NaF) in their deionized drinking water over a fifteen and one‐half week period: 3.4 ppm, 10.0 ppm and 45.0 ppm. In the adequate calcium group a significant increase in flexibility in the rat femur was found only at the 45.0 ppm dosage level. This was not offset by a significant decrease in strength. In the low calcium group a similar significant increase in flexibility appeared at the 10.0 ppm dosage level as well as the 45.0 ppm, but a significant decrease in strength at the two dosage levels was observed. These were in direct relation to the amount of fluoride given.

Experimental osteoporosis and parathyroid activity.

Adult cats fed a low-calcium diet developed osteoporosis. Control cats fed this same diet with added calcium or cats with their parathyroids removed did not develop osteoporosis. The serum calcium and phosphate values in the low-calcium group were lower than in the controls, suggesting that the dietary calcium deficiency causes a decrease of the serum calcium level which stimulates the parathyroids, thus increasing bone resorption and producing osteoporosis. The bone changes are described and related to parathyroid activity and osteomalacia. (Endocrinology 82: 384, 1968)

Effect of a low calcium diet on bone crystallinity and skeletal uptake of Ca45 in rats.

SummaryChemical and X-ray diffraction analyses were performed on femurs of rats receiving a low (0.1%) and high (0.8%) calcium diet with (50 ppm) and without (0 ppm) fluoride supplementaton in the water. In addition, uptake of Ca45 by the ends and shafts of tibia was determined. Bone crystal-linity (i.e., crystal size and/or perfection) was not affected by calcium intake, and the improvement in crystal texture produced by fluoride was the same for the high and low calcium groups. Skeletal uptake of radiocalcium was approximately 20 times higher in calcium deficient animals. Fluoride decreased slightly the uptake of radiocalcium.

CALCIUM AND PHOSPHORUS DETERMINATIONS IN THE BLOOD PLASMA IN RICKETS AND TETANY

Primarily, three groups of cases were selected for blood studies: cases (1) of milk rickets; (2) of typical severe rickets, and (3) of active tetany showing rachitic changes. The cases covered prematurely born, full-term, breast-fed and artificially fed infants. The majority of the infants were between 4 and 12 months of age. The calcium and inorganic phosphorus content of the blood plasma was determined before treatment, and in some cases after treatment. The studies were started with a possibility in mind that rickets might be classified into low phosphorus and low calcium groups, and a third intermediate group; and that certain clinical manifestations might be anticipated by a study of the blood in infants. Howland and Kramer 1 determined the inorganic phosphate of the serum in a series of normal children. They found the concentration to average 5.4 mg. per hundred cubic centimeters, with a minimum of 4 mg. and