Calcified Tissue Research最新文献

1,25-dihydroxycholecalciferol (1,25-(OH)2D3), added at doses which stimulate bone resorption in the system used, did not increase adenosine 3',5'-cyclic monophosphate (cAMP) production in vitro in mouse calvaria incubated for up to 48 h. Thus 1,25-(OH)2D3 does not appear to stimulate bone resorption through involvement of an increased cAMP production.

Electron microscopical observations of the size and shape of bone mineral crystallites have not been in complete agreement with X-ray diffraction findings. The two prevalent viewpoints consider bone mineral crystals to be either rod, or plate like in habit. There appears to be agreement that the smallest dimension of the crystals is about 5 nm, but there is discrepancy in the reported c-axial lengths. The method of dark field imaging is used to obtain a quantitative measurement of the c-axial length distribution in rabbit, ox and human bone: mean c-axial lengths 32.6 nm, 36.2 nm and 32.4 nm, respectively, show no significant difference at the 5% level to the mean c-axial length measured by X-ray line broadening. Both bright and dark field images strongly suggest that bone mineral has a plate like form. Reasons for past discrepancies are discussed.

A child with severe osteogenesis imperfecta was treated with NaF for 8 years, at the end of which time his iliac bone contained 29 mg F/g Ca. Urine F was assayed at intervals for 4.5 years after discontinuing treatment. After the first few days the decline in urinary F excretion can be described by a two component exponential function, with half-times of 5.4 months (10%) and 8.9 years (90%). The latter half-time value is of the same order of magnitude as those observed for F and other "bone-seeking" elements in normal subjects, which suggests that the turnover rate of bone mineral is normal in this disease. Three methods for estimating the attained body F burden at the end of NaF treatment--namely, metabolic balance, bone biopsy, and integration of the exponential function--yielded comparable values.

Vitamin D deficient and phosphate deficient states were produced in young rats by the use of synthetic diets. Whole blood ATP, serum calcium and phosphorus and the ash, phospholipid, hexosamine and hydroxyproline contents of metaphyseal bones of control and rachitic rats were measured after 4 weeks on the diets. There was a decrease in whole blood ATP and serum phosphorus of the rachitic rats, and in the contents of ash, phospholipid and hexosamine of the rachitic metaphyses, while the hydroxyproline contents of the rachitic bones were higher than those of the controls. Subcutaneous injection of ATP or inorganic phosphate in rats, fed a low phosphate diet deficient in vitamin D, caused an increase in serum phosphorus and blood ATP levels and in metaphyseal ash contents. It is suggested that some of the metabolic disturbances in rickets are due to alteration in ATP production.

Fetal rat bones were cultured in either growth-inducing or resorption-inducing media to study mineral losses during bone growth and atrophy in vitro. Whole radii and ulnae from 19-day-old fetal rats, prelabeled with 45Ca and/or 3H-tetracycline, were cultured intact or cut, and then digested by collagenase to obtain the calcified portion of the bones. Three- to five-fold more 3H-tetracycline than 45Ca was lost from the calcified portion when the bones were cultured for 4 days in growth-inducing media. Similar small amounts of 45Ca were lost from live and killed bones, but more 3H-tetracycline was lost from live bones than from killed bones. More 3H-tetracycline was released into the growth medium with a low concentration of calcium (0.5 mM) than when the calcium concentration was high (1.0 mM); no significant difference was seen in the release of 45Ca into the medium at different calcium concentrations. Larger amounts of both isotopes were lost when the prelabeled bones were cultured in resorption-inducing media than in growth-inducing media. When parathyroid hormone stimulated bone resorption in a resorption-inducing medium, equal proportions of both isotopes and bone collagen were lost. Greater losses of 3H-tetracycline than of 45Ca suggest that 45Ca was conserved locally during the resorption that accompanies bone growth, but not during resorption that accompanies bone atrophy.

A method is described for reproducible and rapid quantitative measurements of fractional bone volume in sections of a bone biopsy. The presence or absence of bone is determined at several thousand points over the entire surface area of each specimen by high-speed digitization and computer analysis of video scans of enlarged microradiographic images of bone sections. An operator interactive light-pen assembly permits selective delineation of desired areas of the video image to facilitate computation of regional bone mass within each specimen. Tests of the reproducibility of the method of performed and are described. The results obtained from application of the method to determine the amount of bone in various age groups and in two groups of patients before and after therapy are also presented. These data indicate the potential of this technique for high volume, high resolution measurements of the fractional bone volume in both investigative and clinical diagnostic studies of age dependent and disease dependent processes.