Albumin-induced resorption of fetal rat bone in vitro

The effect of strain of donor eggs, culture conditions, and experimental protocol on release of eggshell calcium by the chick chorioallantoic membrane in vitro

Factors affecting release of calcium by the chick chorioallantoic membrane in vitro were assessed by culturing explants of shell with and without the chorioallantoic epithelium. Explants were removed from eggs on day 16 of incubation and cultured using techniques similar to those used to examine resorption of bone in vitro. The region of an egg from which an explant is removed, the strain of donor eggs used, and addition of bovine serum albumin to the culture medium did not affect release of calcium. In contrast, exposure of explants to a variety of different culture media (DMEM, Medium 199, BGJb, and RPMI) introduced considerable variation in calcium release. Calcium release in vitro was also examined by removing the blunt end of a fertile egg as well as the embryo and yolk. The remaining preparation was filled with culture medium, covered, and cultured for two 24-h periods, with a change of medium after the first 24 h. Preparations from which the chorioallantoic membrane had been removed released very little calcium during culture, whereas those with the epithelium in place released considerable quantities. However, release of calcium by preparations with the membrane declined during the second interval. When surface area is taken into account, such preparations mobilize less calcium than explants cultured under similar conditions.

Dissociation of specific binding of 25-OH-D3 and resorption in fetal rat bones

Specific binding of 25-OH-D 3 was measured in cytosol prepared from isolated fetal rat bone cells. Binding was significant after 2 h incubation at 0 degrees C and appeared to be approaching a plateau at 4 h. Binding was half-maximal at 1.7 X 10(-10) M 25-OH-D3. 24(R),25-(OH)2D3, which was approximately equipotent with 25-OH-D3 in bone culture, had approximately the same binding activity. 1,25-(OH)2D3, which was 2--3 orders of magnitude more active on resorption, was a much weaker competitor for binding. Vitamin D3, which was inactive in culture, was at least as effective a competitor as 1,25-(OH)2D3. The results suggest that the cytosol site which specifically bind 25-OH-D3 is not the mediator of the bone-resorbing activity.

Influence of estrogens on bone resorption in organ culture

Estradiol benzoate, ethinyl estradiol, and human calcitonin were compared for their ability to inhibit the spontaneous or parathyroid extract-induced bone resorption in organ cultures of 19-day fetal rat fibulae. The criteria used for the assessment of bone resorption were: the release of 45Ca from paired prelabeled bone rudiments into the culture medium, the dry weight, and the number of osteoclasts per bone. Estradiol benzoate at concentrations of 1.3 X 10(-5) to 2.6 X 10(-4)M had no effect on the release of 45Ca from fetal fibulae or on the dry weight. Histologically, treated bones were well preserved and resembled the controls. Parathyroid extract (PTE) alone caused extensive bone resorption with numerous osteoclasts and enhanced 45Ca release without weight gain. The addition of estradiol benzoate to the culture medium did not prevent the resorptive action of PTE. Ethinyl estradiol alone provoked a dose-related inhibition of 45Ca release at concentrations of 3.4 X 10(-5) to 1.7 X 10(-4)M. However, this inhibition was accompanied by a decrease in bone dry weight and by various degrees of cellular damage. The same phenomenon was observed in PTE-treated fibulae. Human calcitonin, on the contrary, inhibited the release of 45Ca by decreasing the number of osteoclasts while the weight of the fibulae increased. The inhibitory action of ethinyl estradiol appears to be caused by a toxic effect on bone cells. It is concluded that estrogens have no direct physiological effect on bone resorption in vitro.

Bone resorption in chronic otitis media. A light-microscopical and histochemical investigation of acid phosphatase activity

As a continuation of our previous work, where we have demonstrated that in chronic otitis media the picture in the submucosa-bone marginal zone is dominated by capillary proliferation and occurrence of a mononuclear, histiocyte-like cell containing lysosome-like cytoplasmatic bodies, we now report the presence of considerable activity of acid phosphatase in close relation to the eroded bone. The activity was localized both extracellularly, spread along the bony surface, as well as intracellularly in mononuclear, histiocyte-like cells. The acid phosphatase is the "marker" enzyme for lysosomes, and cells with these lysosomes guarantee the presence of enzymatic activity capable of attacking bone collagen. It is difficult to avoid the conclusion that the lysosomes and their enzymes are directly involved in the processes of bone resorption.