Calcified Tissue Research最新文献

A histomorphometric evaluation of the iliac crest trabecular bone remodeling was performed after tetracycline double-labeling in 41 normal Danes (12 males and 29 females) aged 19 to 56 years. The fraction of formative (osteoid covered) and resorptive surfaces was unrelated to age but higher in males than in females (P less than 0.02 and P less than 0.05, respectively). The appositional rate (0.65 +/- 0.12 micrometer/day) was unrelated to age and sex, whereas the fractional labeled surfaces were higher (P less than 0.01) in the males (0.18 +/- 0.08 micrometer2/micrometer2) than in the females (0.12 +/- 0.05 micrometer2/micrometer2), and among the females inversely related to age (R = -0.38, P less than 0.05). The bone formation rate at BMU level (0.50 +/- 0.20 micrometer3/micrometer2/day) was unrelated to sex, but among the females inversely related to age R = -0.49, P less than 0.01). The bone formation rate at tissue level was higher (P less than 0.02) in the males (0.13 +/- 0.07 micrometer3/micrometer2/day) than in the females (0.07 +/- 0.03 micrometer3/micrometer2/day) and among the females inversely correlated to age (R = -0.43, P less than 0.05). the age- and sex-dependent variations in the dynamic parameters underline the importance of a more elaborated normal material.

White Leghorn chick embryos were injected on the 15th day of incubation with 70 to 300 pmoles 1,25-(OH)2D3. All doses produced hypercalcemia; with the highest dose, the concentration of calcium in serum started to rise 4 h after the injection, reached a peak 20 h after, and was still high 48 h after. Twenty hours after the injection of the same dose, the concentration of inorganic phosphorus in the serum was significantly lower than in the corresponding controls. The tibias from 17-day-old chick embryos injected with 300 pmoles on day 15 were shorter, lighter, and had a lower ash content than those from controls. Histological signs of resorption appeared to be reduced with respect to controls, but no precise quantitation was conducted. The fact that hypercalcemia was not accompanied by hyperphosphatemia may suggest that the vitamin stimulates resorption of calcium from the shell, which is mainly formed by calcium carbonate rather than from the bone from which calcium and phosphate are usually resorbed together.

The mantle edge of the freshwater pulmonate snails Lymnaea stagnalis and Biomphalaria pfeifferi was investigated with histochemical and ultrastructural methods. The mantle edge gland, which is involved in shell formation, consists of the periostracal groove and the belt. This belt appears to be composed of various regions. In the area of the periostracal groove a number of subepithelial gland cell types occur; these release their products into the groove. Between the groove cells ciliated free nerve endings terminate; the corresponding perikarya occur in the subepidermal connective tissue. Also in the posterior belt region free nerve endings were observed between the epithelial cells; in addition, a particular type of subepithelial gland cell was found in this area. The epithelial cells of this part of the belt have the ultrastructural characteristics of ion and water transporting cells; they are probably involved in calcium deposition and resorption. The possible role of the free nerve endings and of the subepithelial gland cells is discussed.

Mithramycin suppresses bone resorption. Its effect on the synthesis and release of beta-glucuronidase (a referent for lysosomal enzymes) in mouse calvarial explants was studied in an in vitro culture system. A newly described medium (designated as KT medium) was introduced in this specific study. Mithramycin initially inhibited the release of beta-glucuronidase into the medium and resulted in an ultimate accumulation of this enzyme in the bone. These results suggest that inhibition of bone resorption by mithramycin may be attributed to interference in release of lysosomal enzymes from bone cells.

Intracellular transport of calcium from the apical to the basal-lateral region of the intestinal epithelial cell was investigated in duodenum from normal fed, fasted, and calcium-loaded rats. The process was followed with time using electron microscopy with potassium pyroantimonate to precipitate calcium. The observations made were subjected to morphometric analysis. The specificity of the method was demonstrated in the villus cell by resistance to microincineration and by absence of deposits following exposure to EGTA. Using this method calcium was seen in cells from calcium-fed rats at the microvillus border, in the Golgi zone, and within the internal compartments of the mitochondria. In cells from fasted rats calcium was not seen. Mitochondria were found largely at the apex of the cell and were free of detectable calcium. By 5 min, in the cells of fasted rats given a calcium load, the calcium had reached the Golgi apparatus and the inner mitochondrial compartment. After 15 min mitochondria were heavily loaded with calcium and had moved to the basal region of the cell. These observations suggest that mitochondria play an important role in absorption of calcium and appear to transport this ion from the apex to the basal region of the cell where entry into the capillaries takes place.

The vitamin D3 metabolite, 25-hydroxycholecalciferol, at concentrations of 0.01 to 10.0 microgram/ml, decreased calcium uptake by isolated bone cells. The effect occurred within 1 min after the simultaneous addition of metabolite and 45Ca. Lactic acid and ATP production by the cells was not affected. 24(R), 25-dihydroxycholecalciferol produced a similar decrease in calcium uptake. Vitamin D3 had no effect at concentrations from 0.01 to 10.0 micrograms/ml. No effect of 1,25-dihydroxycholecalciferol on calcium uptake was observed with concentrations from 0.1 to 100 ng/ml and various preincubation periods extending to 2 h. None of the agents had any effect on calcium efflux. The effects of 25-hydroxycholecalciferol and 24(R), 25-dihydroxycholecalciferol on calcium uptake were not seen in isolated fetal rat skin cell preparations.

Osteoclastic bone resorption involves the solubilization of the mineral salts and the degradation of noncollagen bone matrix and collagen fibrils. As no recognizable collagen fibrils have ever been reported within cytoplasmic vacuoles in osteoclasts, it is generally assumed that the collagen fibrils are digested extracellularly in the resorption zone. The extent to which lysis occurs extracellularly and whether or not the osteoclasts phagocytose the degradation products remain to be established. In the present communication, a hypothesis is presented suggesting the possibility that osteoclastic resorption of bone involves the participation of two different cell types. According to this hypothesis, osteoclastic bone resorption is initiated by osteoclasts that demineralize areas of bone and degrade noncollagen bone matrix. After the osteoclasts have moved away or become partially detached from the demineralized site, the exposed collagen fibrils are phagocytosed by mononuclear, fibroblast-like or monocyte-derived cells.

A comparatively simple quantitative method for assessing bone morphology has been evolved. Microradiographs of thin sections of mandible have been scanned with a Joyce-Loebl double beam recording microdensitometer with a scanning autodensidater attachment, using a white beam. For each image the optical densities for all the pixels (picture elements) were divided into 10 groups. The limits of the division were fixed by the maximum and minimum densities occurring within the image. A computer generated map was produced which indicated the spatial distribution of the pixels within each group to which an arbitrarily chosen shading was attached. The number of pixels within each group is also shown on the map. The computer map was compared with the photomicrograph and, where necessary, the original section. The fractional area of hard tissue was then readily determined using the numerical values of each group of pixels.