No abstract

An experimental study is reported of fracture healing in the femora of 36 Beagle dogs, comparing the results of using stainless steel plates with those of using less rigid titanium alloy plates. The alloy plates led to the appearance of a small amount of periosteal callus without any histological evidence of fracture instability, thus allowing the radiological assessment of fracture union. This also produced less bone loss during the remodelling phase. Radiological measurements 24 weeks after osteotomy showed cortical thickness to be reduced by six per cent under titanium alloy and by 19 per cent under stainless steel, while histological measurements showed a total bone loss of 3.7 per cent under titanium alloy and of 11 per cent under stainless steel plates. Removal of the titanium alloy plates after eight weeks followed by a recovery period of 16 weeks produced an increase of cortical thickness of 69 per cent and a gain in total bone mass of 30 per cent. Titanium alloy plates also produced less soft-tissue reaction than stainless steel plates. It is concluded that this alloy is a promising material for internal fixation devices.

No abstract

Several concentrations of cortisol to M) were tested for their ability to inhibit the spontaneous or parathyroid extract-induced (PTE) bone resorption in organ cultures of 19-day-old fetal rat fibulae. The criteria used for the assessment of bone resorption were: the release of 45Ca from pre-labeled bone rudiments into the culture medium, the dry weight and the number of osteoclasts per bone. At a dose of M, cortisol diminished significantly the release of 45Ca from fetal fibulae. This inhibition was accompanied by a n increase in bone dry weight and by reduced numbers of osteoclasts. PTE, alone, caused extensive bone resorption with numerous osteoclasts and enhanced 'Wa release, without weight gain. This resorptive action of PTE was partially suppressed by cortisol at a dose of M. Lower concentrations were ineffective. Radioautographic studies with 3H-thymidine revealed that cortisol restricts the recruitment of osteoclasts from osteoprogenitor cells, without decreasing the potential of precursor cells to form osteoblasts. PTE, however, stimulates the proliferation of progenitor cells and favors their differentiation towards osteoclasts. This effect can be suppressed by cortisol. It is concluded that cortisol inhibits bone resorption in vitro by limiting the ability of precursor cells to form osteoclasts. Moreover, our study shows that, in fetal rat bones cultured in vitro. osteoclasts arise from locally proliferating mononucleated precursor cells.

In vivo calcium absorption was studied in normal and rachitic chicks. Cytochalasin B (CB) at a concentration of 25 microgram/ml added to the medium inside the duodenal lumen inhibited calcium absorption (20 min) from 82.5 +/- 1.9% of calcium absorbed in the controls to 59.2 +/- 3% in normal and from 70.0 +/- 2.3% to 47.0 +/- 2.1% in rachitic chicks. In vitro studies by everted ileal sacs of young rabbits also showed an inhibition of active transport of calcium due to CB. Whereas in the controls the ratio of 45Ca concentrations in serosal and mucosal media (60 min) was 7.2 +/- 0.32, the ratios were 5.24 +/- 0.52; 4.40 +/- 0.36; 3.40 +/- 0.42; 5.77 +/- 0.52; 1.38 +/- 0.08; and 1.06 +/- 0.02 in the presence of CB at concentrations of 5, 10 and 25 microgram/ml; colchicine 10(-4)M, Na citrate 0.02M, and heat-devitalized conditions, respectively. 45Ca concentration in the mucosal scrapings was also affected. It showed an increase from controls (15,101 +/- 404 cpm/mg) and correlated with CB concentration: 17,378 +/- 489, 19,015 +/- 1000, and 20,201 +/- 362 at 5, 10, and 25 microgram/ml, respectively. Dihydrocytochalasin B also inhibited active calcium transport and caused an increase in 45Ca concentration in the mucosal scrapings. Correlated electron microscopic studies showed certain changes in the brush border, especially in some actin microfilaments in the terminal web region. It seems that these morphological alterations may be related to transcytoplasmic movement of calcium.