Renal discrimination between strontium and calcium in rats

Renal functions were damaged at the reabsorptive site by the injection of cadmium-metallothionein (Cd-MT) and its effect on discrimination of chemically similar elements was examined for the two alkaline-earth elements, calcium (Ca) and strontium (Sr). Tubular damage was induced in female Wistar rats, 7 wk old, body wt 145.1 +/- 3.5 g (mean +/- S.D.), by an intraperitoneal injection of Cd-MT (400 micrograms Cd/kg body wt). The Cd-MT injection caused increases in urinary enzymes (lactate dehydrogenase; alkaline phosphatase), glucose, and total protein. Urinary Ca and Sr increased and urinary Sr/Ca ratio decreased rapidly after the Cd-MT injection. Both changes remained at significant levels throughout the experiment. On the other hand, renal Ca and Sr levels increased with time after 18 or 24 h and changed similarly. Although plasma levels of Ca and Sr slightly increased after 30 or 36 h post-injections, the plasma Sr/Ca level remained constant. A close exponential relationship formed between the relative clearances of Ca and Sr. There was no significant difference between the exponent of the following equation (K) for the Cd-MT-injected group and that for the control group. Sr clearance/creatinine clearance = (Ca clearance/creatinine clearance)K where K = 0.408 from experimental data for the two groups. This suggests that the discrimination mechanism between Sr and Ca during the reabsorptive step in the kidney is strictly regulated.     

Discrimination between strontium and calcium in suckling rats

Discrimination between strontium (Sr) and calcium (Ca) was examined in suckling rats and compared with that in older rats after weaning. Concentrations of Sr and Ca and the Sr/Ca ratios in serum and femur of 10-d old and 21-d old rats were determined. The Sr concentrations and Sr/Ca ratios in the serum and femur of 10-d old rats were lower than those of 21-d old rats, that could be explained by the fact that 10-d old rats ingested only maternal milk in which the Sr/Ca ratio was much lower than the laboratory diet. The relative ratios of Sr/Ca in serum and femur to that in the diet were found to be higher in 10-d old rats compared with those in 21-d old rats, and also higher than those in the older rats after weaning, as described in our previous publication. This result may reflect that discrimination between Sr and Ca during intestinal absorption is lacking in very young animals before weaning and develops after this age. Renal discrimination between Sr and Ca in the suckling rats at 10 d of age was evaluated by determining the relationship between the relative clearances of Ca and Sr. The mathematical model proposed by Walser and Robinson was applied on these results and the parameter for the equation, that is, the discrimination constant, was shown to be higher in 10-d old rats compared to those in young (7 wk of age) and adult (25 wk of age) rats. This result suggests that the discrimination of Sr in favor of Ca during the tubular reabsorptive process may not be fully developed in the very young rats before weaning.     

Interaction between zinc and calcium in skeletal muscle in young growing rats

The purpose of the present study was to determine whether zinc and calcium could interact at the tissue level. In the first part of the study, adult rats were injected with ZnCl₂ dissolved in a physiological saline solution to determine the effects of Zn on Ca levels in various tissues. In the second part of the study, weaned rats (at day 22 postnatally) were fed a diet supplemented with Zn until day 50 and were then sacrificed. In both instances, blood, brain, heart, liver, and skeletal muscle were taken and analyzed. In the Zn-injected group, the brain, heart, and liver showed no interaction between Zn and Ca. The skeletal muscle, in contrast, showed a decrease in Ca in the homogenate, whereas Zn contents showed a significant increase at the sarcoplasmic reticulum (SR). Likewise, in the Zn-supplemented group, the Zn content of the SR vesicle of the skeletal muscle showed an increase, whereas Ca content of the pellet (14,000 g), which contains cell debris, nucleus, mitochondria, and SR vesicles of this group, showed a decrease. Current findings suggest antagonistic effects between Zn and Ca on this tissue. Zn may play a critical role in cellular function through the alteration of itnracellular distribution of Ca in skeletal muscle.     

Kin discrimination in prepubescent and adult Long-Evans rats

The present study investigated the preference of prepubescent and adult rats for an unrelated conspecific over a closely related conspecific (e.g., father, mother). Preference was measured by the amount of time spent in the vicinity of the stimulus animals as well as who was visited first. To prevent mating behavior, stimulus animals were housed behind wire-mesh. Experiment 1 determined if adult female offspring prefer an unrelated, unfamiliar adult male or their father. The preference of adult female rats was independent of kinship. Experiment 2 evaluated the preference of prepubescent female and male offspring for an unrelated, unfamiliar adult male or their father. The preference of prepubescent female and male rats was also independent of kinship. Experiment 3 evaluated the preference of adult male offspring for an unrelated, unfamiliar adult female or their mother. The preference of adult male rats was independent of kinship. In summary, prepubescent and adult rats do not demonstrate preference for kin vs. non-kin (as measured by time spent near stimulus animals or who was visited first). Although kin recognition provides a mechanism for inbreeding avoidance (Wilson, 1987), in the present study adult rats show no evidence of inbreeding avoidance.     

Regulation by calcium of the proliferation of heart cells from young adult rats

Summary Cells of primary and secondary cultures of rat heart ventricle were grown in a medium supplemented with homologous plasma to avoid the non-specific proliferogenic effects of foreign sera. Specific chelation of calcium from the medium arrested the cells' progression through their cycle at the G1 phase. A permanent or brief restoration of the extracellular calcium level (48 hr later) was followed, after a 5 to 6 hr delay, by a burst of DNA synthesis, and the resumption of mitotic activity. NRCC No. 14976.     

Effects of dietary phosphorus intake on bone mineralization and calcium absorption in adult female rats

We investigated the effects of dietary phosphorus (P) intake on the bone mineralization and calcium (Ca) absorption in adult female rats. Fifteen 16-wk-old female Wistar rats were divided into three groups, and respectively fed a low-P diet containing 0.15% P (LP), a control diet containing 0.5% P (C), and a high-P diet containing 1.5% P (HP) for 42 d. The apparent Ca absorption was significantly increased with decreasing dietary P level. The serum parathyroid hormone concentration was significantly lower in the LP group than in the C and HP groups. The serum osteocalcin concentration and urinary excretion of deoxypyridinoline were significantly higher in the HP groups than in the LP and C groups. The bone mineral density of the fifth lumbar vertebra was significantly increased with decreasing dietary P level. These results indicate that the low-P diet increased Ca absorption, this being effective for bone mineralization in adult female rats.     

The effect of stable strontium on the incorporation and metabolism of radioactive strontium in young and adult rabbit bones.

The experiments were performed on 5-, 8-, 12- and 14 months old rabbits. The effect of stable strontium enriched diet on the bone tissue formation (apposition) and on physiocochemical processes consisting in ion exchange were studied using radioactive isotopes: Sr-85 and Ra-226 and tetracycline. The results of kinetic and autoradiographic studies and micoscopical analysis of bone preparations suggest that stable strontium inhibits the mineralization of newly formed bone tissue without affecting the physico-chemical processes related to ion exchange.     

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.     

Bone formation in vitro by stromal cells obtained from bone marrow of young adult rats

Summary Cells from fetal or neonatal skeleton can synthesize bone-like tissue in vitro. In contrast, formation of bone-like tissue in vitro by cells derived from adult animals has rarely been reported and has not been achieved using cells from bone marrow. We have explored development of bone-like tissue in vitro by bone marrow stromal cells. Marrow stromal cells obtained from 40–43-day-old Wistar rats were grown in primary culture for 7 days and then subcultured for 20–30 days. Cells were cultured in either -minimal essential medium containing 15% fetal bovine serum, antibiotics, and 50 g/ml ascorbic acid, or the above medium supplemented with either 10 mM Na--glycerophosphate, 10^-8 M dexamethasone, or a combination of both. Cultures were examined using phase-contrast microscopy, undemineralized and demineralized tissue histology, histochemistry (for alkaline phosphatase activity), immunohistochemistry (for collagen type, osteonectin, and bone Glaprotein), scanning and transmission electron microscopy, energy dispersive X-ray microanalysis, and X-ray diffraction. Collagenous, mineralized nodules exhibiting morphological and ultrastructural characteristics similar to bone were formed in the cultures, but only in the presence of both -glycerophosphate and dexamethasone. Cells associated with the nodules exhibited alkaline phosphatase activity. The matrix of the nodules was composed predominantly of type-I collagen and both osteonectin and Glaprotein were present. X-ray microanalysis showed the presence of Ca and P, and X-ray diffraction indicated the mineral to be hydroxyapatite. The nodules were also examined for bone morphogenetic protein-like activity. Paired diffusion chambers containing partly demineralized nodules and fetal muscle were implanted intraperitonealy in rats. Induction of cartilage in relation to muscle was observed histologically after 40 days in the chambers. This finding provided further support for the bone-like nature of the nodules. The observations show that bone-like tissue can be synthesized in vitro by cells cultured from young-adult bone marrow, provided that the medium contains both -glycerophosphate and, particularly, dexamethasone.     

Disuse-induced deterioration of bone strength is not stopped after free remobilization in young adult rats

The effect of unilateral hindlimb immobilization and subsequent free remobilization on mechanical properties of femur was examined in young adult rats. Right hindlimb of 17 weeks old male rats was immobilized for 2 weeks. Rats were sacrificed either directly after immobilization (E0) or after 4 weeks of free remobilization (E4). Mechanical properties in three-point bending as well as dry mass (m_dry), geometry, apparent density (d_app), and mineralization of dry bone tissue were measured post mortem in right and left femora of experimental rats (E0, E4) and in right femora of age-matched controls (C0, C4). Differences between right femora of experimental and control animals and between right and left femora of experimental animals were analyzed. After immobilization only d_app in E0 was significantly lower than in C0. Side-to-side differences in E0 were present only in m_dry and d_app. Surprisingly, 4 weeks after remobilization the differences between experimental and control femora were more pronounced. Mineralization, d_app, maximum bending moment (M_max), yield bending moment (M_y) and stiffness of the right femur were lower in E4 than in age-matched C4. Side-to-side differences in remobilized rats (E4) were still significant for m_dry and d_app. Additionally, the medullary area was larger, and M_max, M_y, stiffness and work to failure were lower in the right femur than in the left. It is concluded, that the processes of bone deterioration initiated during immobilization do not cease immediately after resumption of normal mechanical loading.     

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.