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This experiment was carried out in order to determine whether the chronic administration of low doses of cadmium resulted in an alteration of the haversian bone remodeling system in dogs. Two pairs of littermate beagles were administered 25 ppm cadmium chloride in their drinking water for 6 months. Four beagles matched for age and sex from the same colony served as controls. By means of fluorescent labeling, we measured haversian bone remodeling parameters according to the techniques described by Frost. Statistical analysis of the results showed significant changes at the 0.01 level in: activation frequency, appositional rates, and number of osteoid seams. At the 0.05 level, significant differences were found in the number of resorption spaces and the bone formation rate. In the absence of other evidence indicative of an alteration in the internal milieu of the dogs, it is concluded that a direct toxic action of cadmium on the mechanisms of activation of cells responsible for the creation and formation of new haversian systems cannot be excluded.

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.

Normal (N-) calf bone consists of lamellae regularly spaced and oriented parallel to the periosteum. The lamellae increase in thickness from the periosteum to the medullary cavity, by apposition of layers of cells and a calcifying matrix on either side of a hypercalcified primer. In the dermatosparactic (D-) bone, the hypercalcified primer is barely visible and the cells are irregularly arranged within the lamellae. The poorly defined vascular spaces are partly filled with an acellular calcified material. In the D-bone, the collagen fibers are sparse and radiate from the vascular space, while in the N-bone they are abundant and laid down concentric with the blood channels. In the D-bone, only a few weeks old, the outer lamellae are radially oriented with respect to the medullar cavity, while haversian remodeling already occurs in the inner part of the diaphysis. At 6 months, the inner half of the diaphysis is made up of normal haversian secondary bone, while the outer half is made up of radial lamellae. The alteration of the mechanical properties of procollagen fibers in the D-bone might be responsible for its defective organization. A resistant fibrous framework, therefore, seems required to ensure the spatial organization of the cells in the calcifying matrix and to maintain its cohesion.

Physical and chemical analysis of the organic matrix of dermatosparactic (D-) bone was performed to evaluate the implication of an alteration in the mechanical properties of procollagen fibers in the process of calcification. The D-diaphyseal bone contained less collagen and more hydroxyapatite than normal (N-) calf bone. Fractionated by centrifugation in a density gradient, D-bone was found to be composed of more than 80% weight of a highly calcified fraction while N-bone of the same age contained only 37% of this fraction. As compared to N-bone, the amount of organic matrix per unit volume of D-bone was increased in the least calcified fractions and reduced in the most mineralized ones. The newly formed matrix of D-bone contained an amount of collagen similar to the N-bone while the concentration of other glycoproteins was higher. Calcification was accompanied, in both types of bone, by a progressive reduction of glycoproteins and collagen; the diminution of collagen was higher in D- than in N-bone. The presence in D-bone of procollagen fibers with altered mechanical properties might be responsible for an excess of glycoproteins in the newly formed matrix. Calcium salt deposition in this matrix and progressive distension of the fibrous framework are two possible mechanisms by which hypercalcification of D-bone occurs.

The secretory territories of rat osteoblasts on the parietal bone were measured directly using scanning electron microscopy. The mean territory of 4620 cells in 19 fields was 154 μm2 per osteoblast. The range for the fields was 136 to 177 μm2 per osteoblast. Four hundred cells were measured individually—for these the mean value per osteoblast was 143 μm2 with a standard deviation of 33. The daily rate of apposition over an 8 day period was 3.12 μm (standard deviation 0.22) measured by tetracycline marking of the mineral front. This gave a daily matrix production rate of approximately 470 μm3 per osteoblast.

The mean wall thickness (MWT) of packets of trabecular bone was measured in undecalcified iliac crest bone samples of 36 normal subjects (14 female and 22 male) under polarized light. The mean wall thickness was 49.7 +/- 8.7 microns at a mean age of 50.9 years. There existed a significant decrease of MWT with advancing age. With an appositional rate of 0.72 micron/day, the mean formation time of iliac trabecular bone packets is 69 days. The decrease of MWT with age corresponds to a decrease in bone formation at the basic multicellular unit (BMU) level with aging and can partly explain the physiological senile osteopenia.

This investigation was undertaken to determine if the metabolic activity of homotypic segments of dog fibulae could be reliably compared in a thirty day period. Activities analyzed were: cumulative formation, porosity, resorption and apposition. Analyses were performed on contiguous tissue sections using microradiographic and tetracycline techniques. Spatial arrangements of the various activities were analyzed by constructing three dimensional models. The data permitted the following conclusions: 1) The mean differences between dog homotypic fibular segments are much smaller than the mean differences between heterotypic sites. 2) The use of homotypic fibular sites as valid controls should be limited to investigations in which the differences worth detecting are at least greater than 4% (apposition), 2% (resorption), 0.6% (porosity), and 2% (cumulative formation). 3) Of the four parameters measured, porosity was the most constant, showing no significant differences between mirror segments. 4) Lag correlations emphasize the importance of utilizing all available contiguous sections in a given specimen. 5) Physiologic resorption was not exclusive in old bone. 6) The sites of metabolic activity were predominantly found among specific active osteons which were primarily distributed peripherally in a strikingly similar pattern between mirror segments.

Young donor rats of an isogenously related strain were injected with3H proline (1 μ Ci/g) and killed from 6 hours to 28 days later. The scapulae were removed, decalcified with EDTA and implanted subcutaneously into the backs of recipient rats. They were removed 14 days later with the surrounding tissue, sectioned, processed for autoradiography and stained with hematoxylin and eosin. In all cases there was a giant cell response round the bone. In bones removed from the donor animals 6 hours after proline injections, the label was on the edge of the appositional side of the bone and the giant cells did not remove it. By 28 days after proline administration when, due to apposition and resorption, the label was on the resorptive side of the bone, giant cells were seen removing the label, which however they did not ingest. It thus appears, as has been suggested in the literature, that recently formed bone collagen is removed with difficulty, but older collagen can be resorbed.

Using an immune-histochemical method, cyclic AMP was localized in cells of periodontal tissues in orthodontically-treated cats. Sixteen cats were treated for periods ranging from 1 hour to 4 weeks. Fresh, frozen, undecalcified 6 mu sections of the tissues were incubated with rabbit anti-cyclic AMP antibodies, followed by sequential incubations with sheep anti-rabbit IgG, rabbit anti-peroxidase IgG and horseradish peroxidase. In the final step, the peroxidase was demonstrated by the diaminobenzidine (DAB) method. It was found that the number of intensely stained cells increased within a short time in areas in which bone resorption or apposition occurred later. However, differences in the pattern of cellular activation were found to exist between areas of compression and tension. The alveolar osteocytes appeared to be affected to only a slight degree by the applications of mechanical forces. These results indicate: (a) that our immune-histochemical method was useful in following the cellular distribution of cyclic AMP during bone remodeling; and (b) that mechanical forces may affect only a small part of the bone cell population and therefore cannot be regarded as an efficient means to bring about extensive bone remodeling.

Mechanical rib testing and geometric analysis were explored as means of evaluating metabolic bone disease. Seventy-nine male patients were examined postmortem. Displacement rate at the loading point and patient age were important variables for which results had to be corrected. Like long bones, ribs apparently undergo progressive circumendosteal resorption with advancing age but unlike long bones, they show no evidence of continued subperiosteal apposition. Effects of selected individual diseases and of all diseases grouped by major organ system were analyzed. Most produced no discernible modification of rib volume, geometry or bending strength as quantified by modulus of rupture. Exceptions were myeloma and arthritis, where the bony material was weakened without remodeling or loss in volume.

Prolonged administration of synthetic salmon calcitonin (SCT) to immature female silver eels, maintained in sea water, provoked a decrease of the serum calcium concentration and an increase of both the osteoblastic apposition and of the degree of mineralization of the intercellular matrix in the vertebral bone. The osteoclastic resorption and osteocytic osteolysis were not significantly affected, however the osteoclastic index was reduced. The ultimobranchial body, site of CT secretion, was cauterized in immature female silver eels maintained in Ca++ rich tap water. This operation resulted in a rise in serum calcium levels with a maximal response after two weeks. After UBX, the vertebral bone osteoblastic apposition stopped completely but the osteoclastic resorption was not modified. The degree of osteocytic osteolysis did not vary. We also observed a significant decrease in the degree of mineralization of the bone organic matrix. The observations made after UBX confirm those obtained after exogenous CT treatment. SCT administered preventively to immature female eels (maintained in sea water), before experimental maturation, inhibited, at least partially, the acute osteoclastic resorption and completely inhibited the bone demineralization induced by carp pituitary extract. The increase of osteocytic ostelysis, usually observed, did not appear.

1. Evidence has accumulated that the rate of acceretion (A) of calcium to bone is the sum of two fluxes; apposition involving the laying down of new bone and augmentation which is the result of slow exchange of non-surface bone calcium with plasma calcium pools as the result of solid state diffusion. 2. A method has been devised for separating A into its two components. It requires the use of45Ca or, for clinical studies,85Sr as a calcium tracer. Studies which are initiated with a combined accretion rate-calcium balance study, are concluded with an estimate of the exponent of the power function which has been found to describe the whole body retention of tracer from the second month onward. 3. The impulse response function of the skeleton for the tracer is then calculated, making the assumption that in any uniform volume of bone, osteoclastic resorption is a first order process. Making in addition certain simplifying assumptions, which are shown to have a modest influence on the final results, a mean rate of bone resorption can be calculated using a development of the well known Stewart-Hamilton formula. The apposition rate is calculated as the sum of the resorption rate and the calcium balance. Augmentation and diminution, defined as equal and opposite exchange processes, are given by the difference between A and the apposition rate. 4. The results of our first thirteen studies in normal subjects and patients with metabolic bone disease are presented, together with analyses of some data from the literature. It is concluded that the development of an atraumatic method for measuring rates of bone formation and resorption in the whole body would be an important advance in the study of metabolic bone disease, and this work is presented so that critical comparisons may be initiated between this tracer method and independent histological methods for measuring these parameters.

Twelve Osborne-Mendel rats were given, for sixty days, an anticariogenic diet where 4% of the sucrose (2.7% of the diet) was replaced by an alkali phosphate salt combination (Na2HPO4+NaH2PO4·H2O+KH2PO4; mole ratios 4.65/0.52/1.00 respectively). Nephrocalcinosis occurred in every animal as small concentric calcium deposits in the medulla and as large calcified masses higher in the cortex. A slight peritubular inflammatory reaction occurred and many exfoliated cells were seen in the lumina of the collecting ducts. In the electron microscope, calcified masses seemed to erode the tubular epithelium. No mitochondrial calcification in the epithelial cells, or calcification in the tubular basement membrane, were found. The cytosomes in a few proximal tubules displayed dark condensations. The ultrastructural features were similar to those found in connection with magnesium deficiency. No calcification was found in 7 controls or in 7 rats receiving the same basic diet with a 4% bicarbonate-phosphate supplement in the sucrose for four months. The appearance of nephrocalcinosis synchronously with a caries-protecting effect and apposition of dental calculus in animals fed on diet supplemented with alkali phosphate is discussed.