Mechanism of induction of hypercalcemia and hyperphosphatemia by lead acetate in the rat

Detrimental effects of maternal lead exposure during pregnancy and lactation on molar development in the young rat

The purpose of this animal study was to investigate the influence of maternal lead exposure during pregnancy and lactation on molar development in the offspring. Scanning electron microscopy revealed no significant differences in the molar morphology among the groups. However, in all the experimental groups, deep, wide cracks were found in the occlusal enamel. Further, the experimental groups had smaller molar diameters than the control group, lead exposure during lactation had a greater influence on the molar size in the offspring, and the groups with the higher dose of lead exposure during pregnancy and lactation had significantly smaller molar sizes than the groups that received the lower dose. The mesiodistal and buccolingual diameters of molars were measured as 3.10 ± 0.07 and 1.95 ± 0.04 mm for control group, 2.97 ± 0.08 and 1.94 ± 0.01 mm for lactation group of low dose, 2.96 ± 0.05 and 1.84 ± 0.02 mm for lactation group of high dose, 3.09 ± 0.06 and 1.94 ± 0.04 mm for pregnancy group of low dose, and 3.02 ± 0.06 and 1.85 ± 0.06 mm for pregnancy group of high dose, respectively.

Influence of lead on the cariostatic effect of fluoride co-crystallized with sucrose in desalivated rats

OBJECTIVE

Results from previous studies have shown that pre- and perinatal exposure to lead enhances susceptibility of rats to development of dental caries. A possible explanation for this phenomenon may be that lead complexes with fluoride and renders F insoluble and unable to exert its cariostatic effects.

MATERIALS AND METHODS

Thus, to explore this hypothesis, 48 desalivated Sprague-Dawley rats were placed in a König-Höfer programmed feeder and received 17 meals of powdered sucrose daily, and water ad libitum as follows: group (1) plain sucrose and sterile distilled water (SDW); (2) sucrose containing 15 ppm F and SDW; (3) sucrose containing 15 ppm F and 10 ppm Pb water; (4) sucrose containing 15 ppm F and 25 ppm Pb water.

RESULTS

The highest smooth-surface, sulcal surface caries and severity scores were observed in group I. Animals that were exposed to fluoride showed reduced smooth-surface caries and severity scores. S. sobrinus counts did not differ among the groups.

CONCLUSION

Lead did not interfere with the protective effect of fluoride in the conditions of the present study.

Time course of stomach mineralization, plasma, and urinary changes after a single intravenous administration of gadolinium(III) chloride in the male rat

In a previous experiment it was reported that the intravenous administration of gadolinium chloride (GdCl3) to rats results in a discrete band of interstitial mineralization in the fundic glandular mucosa of the stomach. To investigate the time course for the development of this lesion and its relationship to plasma calcium and phosphate concentrations, 2 experiments were carried out in male Sprague-Dawley rats given a single intravenous dose of 0.07 mmol/kg GdCl3. Plasma calcium and phosphate concentrations approximately doubled between 30 min and 12 hr postdose but had regressed back to near normal values by 24 hr. However, there were no observable clinical signs in treated animals. Histologically, there was progressive mineralization of the lamina propria of the neck region of the fundic glands from 6 hr postdose, forming a distinctive mineral band by 12 hr postdose. At 7 and 14 days postdose the mineral deposits were accompanied by mucous cell hyperplasia, interstitial fibrosis, and a very sparse infiltration of inflammatory cells. By 56 days postdose only occasional mineral deposits remained. Transmission electron microscopy showed mineral first nucleated on collagen in the interstitium, but there was no evidence of cell necrosis. X-ray microanalysis showed that the interstitial mineral was composed of calcium and phosphate in the form of hydroxyapatite; gadolinium (Gd) was only very rarely identified. These findings are consistent with metastatic mineralization. The source, cause, and the exact nature of the excess plasma calcium and phosphate are unknown, and the possible significance of this effect for clinical use of Gd-containing chelates in nuclear magnetic resonance imaging requires further investigation.

Stimulative effects of lead on bone resorption in organ culture

To clarify whether hypercalcemia after injection of Pb to rats is due to biological bone resorption or physicochemical mineral dissolution, the effect of lead (Pb) on release of previously incorporated 45Ca in organ culture was investigated. Pb at 50 microM and above stimulated the release of 45Ca and hydroxyproline (Hyp). Pb did not stimulate 45Ca release from the bones inactivated by freezing and thawing. Eel calcitonin (ECT), bafilomycin A1 and scopadulcic acid B (SDB) inhibited Pb-stimulated 45Ca release. These results indicate that Pb-induced 45Ca release is due to osteoclastic bone resorption. Pb-stimulated bone resorption was inhibited by indomethacin and flurbiprofen. Pb stimulated the release of prostaglandin E2 (PGE2) from the bones into the media. There was significantly high correlation between 45Ca and PGE2 release. Pb-induced bone resorption was inferred to be mediated by PGE2. From these results, it was suggested that hypercalcemia after Pb injection might be caused by biological bone resorption.

The effect of lead acetate on dentine formation in the rat

The intravenous injection of lead acetate produces a response in dentine by formation of the so-called lead line. This is associated with a rapid but temporary rise in serum calcium and phosphorus. Previous studies have suggested that lead replaces calcium and phosphorus in the apatite lattice. In this study the lead line was investigated in the scanning electron microscope using backscattered electron imaging and was shown to consist of continuous hypomineralized interglobular spaces within the dentine. Dentine formation was disrupted for at least a week after injection of lead ions. With energy dispersive analysis by X-rays, no localized concentration of lead was detectable within the 'lead line'. It is suggested that the lead line results from a direct effect of lead on the odontoblasts and other hard tissue-forming cells producing a rapid loss of intracellular calcium temporarily displaced by lead ions and a subsequent disturbance of local calcium metabolism.

Comparison of biometric data of children with high and low levels of lead in the blood

This paper deals with a biometric study of 312 boys and girls, aged 2.5-16 years, living in an area with a long history of pollution by lead. The aim was to search for eventual relationships between ten biometric variables and measures of lead absorption in the bodies, i.e. the amount of lead in the blood (PbB), of these children. Standardized values of the biometric variables were compared in the high-PbB and low-PbB categories, by multivariate analysis of variance. Comparison of the vectors of the ten biometric variables reveals a significant difference between the two categories of PbB levels. We found some evidence that the younger children (below 8 years of age) are more likely to absorb lead in the body and are more vulnerable to the effects of subclinical lead intoxication than their older counterparts. The differences between the averages of biometric variables in the two PbB categories are consistently (although not significantly) greater among younger children. This trend disappeared in the older age group. These results confirm data from the literature that young children are especially at risk. It can be concluded that there is a subtle, but significant, influence of lead absorption on the biometric profiles of children and that this effect is probably more important in children below 8 years of age.

Calcitonin and phosphate

This report summarizes the relationship of calcitonin to phosphate. The hypocalcemic action of calcitonin is dependent upon phosphate, while the hypophosphatemic action is independent of calcium. Calcitonin moves phosphate into bone cells and bone fluid in contrast to reducing the movement of calcium from bone to blood. Calcitonin acts rapidly and at low doses on the osteocytes and lining cells at bone surfaces. Morphological changes can be identified within 7 min. This action causes the accumulation of an electron-dense material both in bone lining cells and their microenvironment. It is postulated that both the hypocalcemic action of calcitonin and its ability to cause an accumulation of material at bone surfaces may result from the movement of phosphate into these areas. The biochemical action which could produce the phosphate movement is unknown. The possibility is suggested that calcitonin increases phosphate transport into bone cells.

Lattice parameters and cation distribution of solid solutions of calcium and lead hydroxyapatite

Solid solutions of calcium hydroxyapatite (CaOHA) and lead hydroxyapatite (PbOHA) of the formula Ca10-x Pbx (PO4)6 (OH)2 were prepared by coprecipitation followed by heating at 800 degrees C in a steam of CO2-free water vapor of 1 atm. The samples were apatitic in the range 0 less than x less than 6 and contained lead phosphates as a second phase at higher Pb/Ca ratios. Lattice parameters and cation distribution of the apatitic samples were determined by X-ray diffraction. The lattice parameters varied linearly with x in the range considered, whereas all Pb2+ were located in the six-fold position for cations. There was a miscibility gap in the apatite series of solid solutions in the range 1 less than x less than 4, whereas apatites in the range 6 less than x less than 10 were not stable under the conditions of preparation. It is concluded that apatites in the range 4 less than x less than 6 represent a minimum in the free energy of solid solutions between CaOHA and PbOHA.