Haversian bone-remodelling rates in the beagle after cessation of exposure to chronic low doses of lead.

This study reports the changes observed in bone-formation dynamics at the cell, tissue and organ level in cortical bone in four standardization research colony-raised male Beagles that were exposed to 0.7 mg of lead acetate per day for 6 months, followed by a 6-month period when no lead acetate was given. Four similar age-sex matched Beagles of the same origin served as controls. Tissue and blood lead levels were measured. Biochemical and hematological analysis were carried out on a monthly basis. Plasma levels of immunoreactive parathyroid hormone were measured. In the absence of any alteration of the dogs' internal milieu, following 6-months exposure to lead there was a decrease in bone formation at the cell (70 percent), tissue (66 percent) and organ (66 percent) levels. Six months after the lead exposure was interrupted, bone formation returned to normal (93 percent at tissue and 100 percent at organ levels), but there was still some depression of activity at the cell level (70 percent). It is not known whether that cell-level depression of activity is due to persistent enzymatic inhibition following the 6-months exposure or whether it is due to the fact that the cell continued to operate in a micro-environment in which tissue levels of lead are elevated, or both.

The effect of chronic administration of trisodium nitrilotriacetate (Na3NTA) on the haversian remodelling system in dogs.

Trisodium nitrilotriacetate from the environment is reported to accumulate in bone. Two skeletally mature male littermate beagles were administered Na3NTA in a concentration of 2.5 mg/kg body weight in their drinking water for a period of 7 months. Rib biopsies were obtained from the dogs after fluorescent labelling before and at the end of the experimental period. Blood levels of zinc were measured at the same times. Twenty-two similar dogs from the same colony acted as controls. We noticed a decrease in radial closure rates and percent osteoid seams labelled between the experimental and the control animals which was statistically significant at the 0.05 level. The serum levels of iPTH and the bone levels of zinc showed no statistically significant difference. Accepting the fact that the treatment population was small and that the changes observed--although statistically significant--were minimal, it cannot be discounted that the exposure of these animals to Na3NTA for a longer period of time would not have had a more adverse effect on haversian bone remodelling activity.

Appositional bone formation rates in the Beagle.

Measurements of haversian appositional bone formation rates were carried out on 400 haversian systems in 28-month-old standardized research colony-raised Beagles, using the midshaft of the 11th rib. The appositional bone formation rate was gradual and regular when the circumference of the outer tetracycline ring was more than 0.35 mm, but the regularity of the measured rate disappeared when the outer tetracycline ring circumference was less than 0.35 mm. Erroneous conclusions could be drawn from measurements of appositional bone formation rate in these animals if this fact were not taken into consideration, and we concluded that in pre- and postexperimental biopsy sections in the ribs of these animals, haversian systems with tetracycline ring circumferences above 0.35 mm must be measured in both situations if the differences in appositional bone formation rate are to be construed as being truly significant.

Age-related variations in cortical bone-remodeling measurements in male Beagles 10 to 26 months of age.

Age-related variations in bone-remodeling rates in the male Beagle were unknown. Variations were examined in 28 male Beagles whose ages were evenly distributed between 10 and 26 months. Results were analyzed by computer and regression lines for a best fit line for each determination were given; the 95% confidence limit for the best-fit line and the 95% confidence limits for the individual measurements were calculated. The results are graphically presented in this paper. There was a slight increase in total cortical area, although there was a decrease in the ratio of total-to-cortical area. Osteoid seams showed a frank decrease. Relatively little variation was found in circumference of osteoid seams and appositional rate. The number of resorption spaces decreased. There was a decrease in radial closure rate. Marked decreases were found in activation frequencies and bone formation rate. Increases were observed in osteon formation times and ratio of resorption to formation. The width of osteoid seams and the percentage of systems labeled decreased slightly. As a result of these experiments concerning variations in bone-remodeling activity carried out on Beagles (using the same dogs as their own controls), it was concluded that results obtained should be compared with the expected age-related activity of bone remodeling and not with the initial preexperimental biopsy results.

Plasma levels of immunoreactive parathyroid hormone in dogs chronically exposed to low levels of cadmium chloride.

A previous report had suggested that chronic cadmium intoxication interfered with calcium accumulation in bone and suggested that the mechanism may be a parathyroid-induced bone resorption. We measured C-terminal parathyroid hormone levels in the blood of four male standardized research beagles chronically exposed during 6 months to 25 ppm cadmium chloride in their drinking water while at the same time we performed measurements of the parameters of haversian bone remodelling activity. We failed to demonstrate any statistically significant difference in levels of this hormone in the experimental dogs before or during the exposure, or between samples obtained from the experimental dogs at the end of their period of exposure and normal untreated control dogs from the same colony. We conclude that in the early stages of chronic cadmium intoxication before there is evidence suggestive of intestinal or renal malfunction that may secondarily involve the parathyroid glands, the alteration observed in haversian bone remodelling rates is not mediated through abnormalities of function of the parathyroid glands.

Studies on bone-remodeling rates on the Beagle: A comparison between similar biopsy sites on different ribs.

Two male littermate standardized colony-raised Beagles were studied to find out whether there was any statistically significant difference in the measurements of bone-remodeling determinations at similar sites on different ribs of the animal. Tetracycline fluorescent-labeling studies were performed on these animals, the midportion of the proximal, midshaft, and distal thirds being sampled from the 5th, 7th, 9th, and 11th ribs. Statistical analysis of the findings indicates that there is no significant difference in bone-remodeling activity between similar sites on alternate ribs. This fact permits studies on bone-remodeling activity in an animal to be done in which the same animal is used as its own control and in which more than two experimental biopsy samples are required.

Effect of chronic low-level cadmium intoxication on the Haversian remodeling system in dogs.

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.

Dense mineralized perivascular tubules in osteopetrotic bone.

Samples of osteopetrotic bone were deorganified and examined with the scanning electron microscope. Densely mineralized tubules with walls measuring from 1-10mu in width and with a luminal diameter of 70-90mu were observed scattered throughout the processed surface of the bone. Adjacent sections of bone prepared by routine histological methods for light microscopy showed that the tubules occur in areas of bone where "hyaline" structures are seen surrounding blood vessels. The tubules are not present in normal bone. The nature of these tubules and their possible significance in the pathological physiology of osteopetrosis requires further investigation.

Bone-remodeling rates of the Beagle: a comparison between different sites on the same rib.

The standardized colony-raised male Beagle is being used more frequently for research purposes. The rib of this dog is an ideal bone on which to measure haversian bone-remodeling activity. To date there has been little indication as to whether there has existed any natural statistically significant differences in bone-remodeling rates along the length of the rib of this dog. To answer this question, standard samples were procured from the proximal, mid-shaft, and distal portions of the 5th, 7th, 9th, and 11th ribs after tetracycline labeling. It was found that there exist in the normal state statistically significant differences between the 3 portions on all the ribs examined, as refers to ratio of cortical to total bone area, number of osteoid seams, number of resorption spaces, activation frequency, and bone-formation rate. These differences are significant at the 0.001 level and may give rise to a wrong interpretation by the unwary investigator. The results of this investigation stress the importance of standardizing the biopsy site on the rib that is to be examined.

Microstructural organization of human and bovine cruciate ligaments.

Human and bovine anterior cruciate ligaments studied with the SEM demonstrate fascicular bundle and connective tissue sheath components. In the human, collagen fibers of the connective tissue sheath, although approximately the same diameter as the fascicular fibers, have an orientation suggestive of a binding rather than a tensile function. While both elements have tensile properties, it is hypothesized that the contribution from the sheath component is minimal and, consequently, detailed studies of the tensile properties of ligaments will produce meaningful data when related to the appropriate cross-sectional areas. In direct contrast to the human counterpart, the SEM appearance of bovine cruciate ligaments is tendon-like, characterized by very dense subfasciculi surrounded by very thin connective tissue sheaths.

The effect of chronic low level lead intoxication on the Haversian remodeling system in dogs.

The greatest portion of lead ingested by human beings or experimental animals is stored in bone. Once in bone, lead is difficult to remove. It may have a half-life of 20 years or more and could interfere with bone metabolism. The effects of lead intoxication on the production of intercellular matrix have been reported previously but the effects of lead on bone turnovers rates were not reported. In this paper we reported the results of a study of the effects of lead on bone turnover in dogs. Differences between experimental and control dogs were found when measuring appositional rates, radial closure rates, activation frequencies, osteon formation times, and bone formation rates. We found that dogs subjected to a low dose (1.3 mg. per kg. per day) of lead over a long period of time (201 days) showed a statistically significant decrease in bone formation activity at the cell (90 per cent), tissue (85 per cent), and organ (78 per cent) levels when compared to controls. Although these observations were made on a small experimental and control sample (four dogs), they suggest that chronic low dose lead intoxication does alter normal bone physiology.

Experimental retinal dysplasia due to cytosine arabinoside.

Retinal dysplasia was produced in newborn rats treated postnatally with the antimitotic substance, cytosine arabinoside (ara-C). In rats examined from 6 to 60 days, there were numerous retinal rosettes surrounded by photoreceptor cells and bipolar cells containing photoreceptor cell processes, displaced nuclei, and cellular debris. Abnormal development and alignment of photoreceptor cell processes were commonly observed. Cellular degeneration was evident at all ages, and infiltrating phagocytic cells were especially numerous in the retina of treated rats examined at 60 days. Characteristic features of ara-C-induced retinal dysplasia included the scattering of bipolar cell nuclei in the inner and outer nuclear layers and marked reduction in the width of the affected retina. Considerable retinal and cerebellar development occurs postnatally in the rat, thus newborn animals might be useful in the testing of possible teratogenic drugs.

Scanning electron microscopic observations on bone.

The maceration technique employed in the preparation of specimens of bone for museum purposes has also been found to be of use in the preparation of fresh specimens for study with the scanning electron microscope. The technique requires less technical supervision, permits a greater underprocessing to overprocessing margin, and allows comparability of recent biopsy material with previously macerated bone specimens with no less detail than that found by other authors using other techniques on biopsy material.