241-Am in the beagle skeleton: microdistribution and local dosimetry.
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Americium↗
Biomedical subjects
W S Jee
Publications and source records attributed to W S Jee.
Electrophysiological properties of osteoblastlike cells from the cortical endosteal surface of rabbit long bones.
The mean transmembrane potential of cultured osteoblastlike cells isolated from the cortical endosteal surface of rabbit long bones was -16.9 +/- 0.64 mV (n = 335). Elevation of potassium concentration in medium caused a decrease in potential. As the external concentration of potassium reached 15 mmol/liter and above, there was a linear relationship between the potassium concentration in log scale and the membrane potential with a slope of -13 mV per 10-fold change in external potassium concentration. Dibutyryladenosine 3',5'-cyclic monophosphate, parathyroid extract, hydrocortisone, and sodium fluoride all depolarized the membrane of osteoblast-like cells after both short (1-2 h) and long (24 h) exposures at suitable doses, whereas calcitonin and prostaglandin E2 hyperpolarized the membrane after long exposures. The Na+, K+ and Cl- concentrations of cultured osteoblastlike cells were 0.538, 0.984, and 0.358 mmol/g protein or 52.6, 96.3, and 35.0 mmol/liter cell water, respectively. The protein content of these cells was 8.18 +/- 0.6 g/100 g cells and the water content was 83.7 g/100 g cells. The above-mentioned chemical and hormonal preparations in doses that produced significant changes in the membrane potential of these cultured cells did not alter their electrolyte or protein contents 24 h after exposure. Intracellular pH of cultured osteoblastlike cells as determined by [14C]-dimethyloxazolidine-2,4-dione and 3H2O averaged 7.03 +/- 0.11 when the pH of culture medium was maintained at 7.4. Calculations based on the values for the membrane potential and the electrolyte concentrations observed in this study indicate that Na+, and H+, and Cl- are actively transported out of the cells and K+ into the cells.
Animals↗
Changes in endochondral bone elongation rates during pregnancy and lactation in rats.
The rates of endochondral bone elongation during pregnancy and lactation in rats have been studied. The rate of growth at the distal femoral epiphyseal growth plate was measured using fluorescent bone markers. Endochondral growth rates were substantially increased in pregnant animals when compared with age-matched, nonmated controls. There were also increases in growth plate thickness, hypertrophic cell lacunar height, and the calculated rate of cell production during pregnancy. At parturition, this growth trend was reversed and during lactation there were significant decreases in endochondral growth rates. There were also corresponding decreases in growth plate thickness, hypertrophic cell lacunar height, and the calculated rate of cartilage cell production. These results indicate that significant changes occur in maternal endochondral growth rates during the reproductive cycle in rats.
Animals↗
Membrane potentials, electrolyte contents, cell pH, and some enzyme activities of fibroblasts.
The resting membrane potential of the cultured fibroblasts derived from rabbit subcutaneous tissues was -10.2 +/- 0.20 mV (n = 390). This potential was affected by the potassium concentration in the culture medium, but not by other chemical or hormonal preparations, such as dibutyryladenosine 3',5'-cyclic monophosphate (0.5 to 5.0 mmol/l), sodium fluoride (10(-5) to 10(-4) M), hydrocortisone (10(-7) to 10(-6) M), parathyroid extract (0.5 to 1.0 U/ml), or thyrotrophin (5 to 10 mU/ml). The Na+, K+, and Cl- concentrations of the cultured fibroblasts were 35.4, 85.7, and 22.6 mmol/l cell water, respectively. The water and protein contents of these cells were 82.1 and 9.18 g/100-g cells, respectively. The intracellular pH of fibroblasts as determined by [14C] dimethyloxazolidine-2, 4-dione, and 3H2O ranged between 6.9 and 7.1 when the pH of the culture medium was maintained at 7.4. The activities of Na+, K+-, HCO3(-)-, and Ca++, Mg++-ATPases in these cultured cells were 19.0 +/- 2.1, 13.6 +/- 2.1, and 6.6 +/- 1.2 nmol pi/mg protein per minute, respectively, and the carbonic anhydrase activity was 0.054 U/mg protein. Calculations based on the values for the membrane potential and the electrolyte concentrations observed in this study indicate that Na+, K+, Cl-, and H+ are not distributed according to their electrochemical gradients across the cell membrane. Na+, Cl-, and H+ are actively transported out of the cells and K+ into the cells.
Adenosine Triphosphatases↗
Ion-transporting ATPases and matrix mineralization in cultured osteoblastlike cells.
Cultures of osteoblastlike cells obtained from the endosteal surfaces of rabbit long bones formed and mineralized an extracellular matrix when they were supplied daily with medium containing fresh ascorbate. No matrix formed without this supplementation. The matrix mineralized whether or not beta-glycerophosphate, a substrate of alkaline phosphatase, was added to the medium. The ion-transporting ATPase activities of untreated, ascorbate-treated, and ascorbate plus beta-glycerophosphate-treated cells were measured. Ascorbate-treated and ascorbate plus beta-glycerophosphate-treated cells had similar enzyme activities. The activities of the Ca2+-ATPase; Ca2+,Mg2+-ATPase; and alkaline phosphatase in treated cells were elevated over the activities in untreated cells. Na+,K+-ATPase activity was lower in treated than in untreated cells. HCO3--ATPase activity was not changed by treatment. Alkaline phosphatase activity was 20 times higher in freshly isolated osteoblastlike cells than in cells grown to confluence in primary culture. In addition, subculturing further reduced the activity of this osteoblast-marker enzyme. The activities of the ion-transporting ATPases and alkaline phosphatase in second passage cells were similar to the activities of these enzymes in fresh, noncalcifying tissues. Nevertheless, second passage cells retain the ability to mineralize an extracellular matrix, and their ion-transporting ATPase and alkaline phosphatase activities are altered when the cells mineralize a matrix.
Adenosine Triphosphatases↗
Effects of cortisol and fluoride on ion-transporting ATPase activities in cultured osteoblastlike cells.
Na+,K+-ATPase, HCO3(-)-ATPase, Ca2+,Mg2+,-ATPase, Ca2+-ATPase, and alkaline phosphatase activities were measured in cultures of osteoblastlike cells treated with fluoride and cortisol separately and in combinations. Low concentrations of cortisol increased HCO3- -ATPase (10(-11) to 10(-18) M cortisol) and alkaline phosphatase (10(-11) to 10(-9) M cortisol) activities, but higher cortisol concentrations reduced these activities. Na+,K+-ATPase, Ca2+,Mg2+-ATPase, and Ca2+-ATPase activities tended only to be reduced by cortisol. Fluoride (10(-6) and 5 X 10(-6) M) increased HCO3(-)-ATPase and alkaline phosphatase activities, but these activities were similar to controls in the presence of 10(-5) M fluoride. Ca2+,Mg2+-ATPase activity was decreased and Na+,K+-ATPase activity was increased as the concentration of fluoride increased (10(-6) to 10(-5) M). Preliminary experiments with fluoride indicated that lower concentrations (10(-7) M) were without effect. Cortisol concentrations of 10(-9) and 10(-8) M were chosen for studies with combinations of cortisol and fluoride because the effects of these concentrations on alkaline phosphatase activity were opposite, i.e. 10(-9) M increased whereas 10(-8) M decreased activity. Fluoride concentrations of 10(-6), 5 X 10(-6), and 10(-5) M were chosen because a peak of alkaline phosphatase activity occurred at 5 X 10(-6) M fluoride. Higher (10(-4) M) and lower (10(-7) M) fluoride concentrations were without effect. The effects of combinations of cortisol and fluoride depend on the enzyme activity measured. Fluoride (10(-6) M) combined with cortisol (10(-9) M) produced a peak of Na+,K+-ATPase activity. The increased activity obtained with all concentrations of fluoride alone was preserved when fluoride was combined with 10(-8) M cortisol, although the activity tended to be reduced at 5 X 10(-6) and 10(-5) M fluoride. HCO3(-)-ATPase activity was increased by fluoride combined with 10(-8) M cortisol and decreased by fluoride combined with 10(-9) M cortisol compared to the activities obtained with fluoride alone. The decrease in Ca2+,Mg2+-ATPase activity caused by fluoride alone was prevented by 10(-9) and enhanced by 10(-8) M cortisol, although all treatments produced the same activity at 10(-5) M fluoride. Ca2+-ATPase activity tended to be increased by combinations of fluoride and cortisol, but significantly so only at 10(-5) M fluoride in combinations with 10(-8) and 10(-9) M cortisol.(ABSTRACT TRUNCATED AT 400 WORDS)
Adenosine Triphosphatases↗
Microdistribution and localized dosimetry of 241Am in bones of beagle dogs.
The microdistribution of 241Am in selected bones of seven beagle dogs was analysed using a computer controlled microscope photometer. Four of the animals receiving between 102.5 and 165 kBq/kg were killed between 7 and 20 days after injection, and three animals receiving 32.9-34.0 kBq/kg were killed between 1300 and 1569 days. Using the photometric scanning technique, the concentrations of 241Am in several anatomical regions, as well as the specific surface activities and their variations, dose rates, accumulated radiation doses, burial depths and morphometric parameters, were derived. Dose rates to the 0-10 micron marrow band adjacent to surfaces were found to be between 8.6 and 15.7 times higher than the average skeletal dose. Accumulated radiation doses from initial deposits to lining cells were estimated to be between 87 and 252 Gy. The average burial depth in the animals killed at later times was around 8 micron. Morphometric parameters showed that radiation damage occurred in these animals, resulting in abnormal trabecular architecture. A positive correlation between specific surface activity and local turnover rates was established.
Americium↗
Morphometry of bone cell nuclei and their location relative to bone surfaces.
The shapes and locations of lining cells, osteoblasts and osteoprogenitors in sections of rat bone have been quantified by means of a digitiser. The nuclei of all three types of cells can be characterised by oblate spheroids (ellipsoids of revolution). The axis dimensions, their relative variations and the correlation between these parameters have been determined by computer simulation. The nuclear volume of progenitors (288 microns) is more than twice the volume of osteblasts and lining cells (127 microns and 113 microns, respectively). The true mean perpendicular distances of nuclei are 3.1 microns, 5.7 microns and 7.7 microns for lining cells, osteoblasts and progenitors, respectively. The probability densities for true perpendicular distances have been calculated and analytical expressions are given that formally characterise these densities.
Animals↗
Effects of dietary calcium, phosphorus and magnesium on intranephronic calculosis in rats.
The effects of varying dietary levels of calcium, phosphorus and magnesium on the incidence and severity of intranephronic calculosis were studied. Renal calculi were induced by feeding female rats the AIN-76TM semipurified diet for 4 weeks. During this time period, dietary levels of 350, 450 or 550 mg calcium per 100 g diet did not influence the occurrence of urolithiasis. Increasing dietary magnesium levels from 50 to 350 mg was beneficial in preventing the occurrence of calculi if the diet contained 400 mg or less phosphorus. The protective effects of dietary magnesium were counteracted when dietary phosphorus levels were increased from 400 mg to 550 or 700 mg. If the dietary content of phosphorus and magnesium permitted the formation of renal calculi, the severity of the condition was also influenced by the dietary level of calcium. Some animal groups fed semipurified diets did not have microscopic or radiographic evidence of renal calculi but were found to have significantly elevated renal calcium values. It was suggested that these animals might be in a precalculus-forming state.
Analysis of Variance↗
Effect of diet and intranephronic calculosis on bone modeling and parathyroid volume in rats.
The effects of diet and intranephronic calculosis on bone modeling parameters and parathyroid volumes in the rat were studied. Bone chemical analyses and histomorphometric evaluation indicated that a modified AIN diet, containing minimal required levels of calcium, phosphorus and magnesium, was not nutritionally adequate. Although the mineral content of the modified AIN diet barely met the demands for normal bone modeling, both the AIN-76TM and modified AIN diet caused intranephronic calculosis. Nephrolithiasis was not observed in rats fed a natural-product diet. After 10 days, the medullary cavity size and the index of resorption were slightly greater in rats fed the calculogenic diets, but these effects were not evident at 9 weeks. A slight but highly significant difference in the bone magnesium content was observed between rats fed the semipurified and natural-product diets. At 9 weeks, the parathyroid volumes were slightly increased in rats fed the AIN-76 diet compared to rats fed the natural-product diet. It was concluded that differences in dietary content that promote or inhibit intranephronic calculosis do not alter intestinal absorption as much as they influence molecular and cellular events occurring after absorption.
Animal Nutritional Physiological Phenomena↗
The relationship of bone marrow type and microvasculature to the microdistribution and local dosimetry of plutonium in the adult skeleton.
Most plutonium-induced bone tumors in beagles arise in trabecular bone sites surrounded by hematopoietic tissue. The microvasculature and the relative incorporation of 241Pu (a low energy beta emitter) on trabecular bone surfaces from red and fatty marrow sites were studied in the adult beagle. The vascular volume, as determined by India ink perfusion, was about 16% in the red marrow and about 2% in the fatty marrow. The red marrow has large vascular sinusoids with a discontinuous endothelial lining whereas fatty marrow has a closed capillary bed. Plutonium concentrations on bone surfaces of red marrow sites are about 0.43 pCi/cm2/nCi/kg of injected dosage, a factor of eight greater than at fatty marrow sites (0.053 pCi/cm2/nCi/kg). The differences in the bone marrow microvasculature between red and fatty marrow help to explain differences in plutonium incorporation and local bone physiology in these skeletal sites. These observations may relate to the nonuniform distribution of plutonium-induced osteosarcomas observed in adult, long-lived mammals.
Animals↗
Radiation dose rates to the proximal humerus of growing beagles injected with 239Pu.
The anatomical distribution of 239Pu in the proximal humerus was studied in four beagles injected at 90 days of age and sacrificed 7, 28, 56, and 128 days after injection, respectively. Initial deposition in each humerus was 3.1% of the injected Pu; 41% of that was retained with a net halftime of 248 days; for the remaining 59% no decrease was observed with time. Sixty-one percent of the initial deposit was concentrated in the proximal epiphysis and metaphysis. Average radiation dose rates to trabecular bone of the epiphysis, to those parts of the metaphysis that were formed before and/or after injection, and to the area corresponding to the primary and secondary spongiosa were determined by fission track autoradiography. Local dose rates within the range of 10 microns of the endosteal surface, to the marrow and to osseous tissue were calculated. Because of the rapid growth and modeling rate, surface deposits declined rapidly. In the metaphysis, bone formed after injection contained less than 1/2 the Pu concentration of bone which was present at the time of injection. At 100 days of age, bone mineralization as determined by the ash weight/wet weight ratio, and the fraction of bone volume occupied by mineralized tissue was 1/2 that seen in young adult beagles. The surface/volume ratio was twice as high as in young adult beagles. The possible effects of local radiation doses were correlated with areal densities of cells and types of cells at risk. Comparisons were made with corresponding sites from the humerus of beagles injected as young adults.
Aging↗
Studies on the role of vitamin D in early skeletal development, mineralization, and growth in rats.
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Animals↗
Skeletal retention and distribution of 226Ra and 239Pu in beagles injected at ages ranging from 2 days to 5 years.
The age at exposure significantly affects the retention and distribution of 226Ra and 239Pu, both of which deposit in the skeleton although in somewhat different patterns. Beagles aged 2 days (neonates), 90 days (juveniles), 18 months (young adults), or 5 yrs (mature) received a single subacute injection of one of these nuclides and were sacrificed serially during a 2-yr interval. Nuclide concentrations in plasma, the skeleton, individual bones and bone sections were determined and retention equations were calculated. The microanatomical skeletal nuclide distribution was studied after fission track or conventional autoradiography. Elimination of 239Pu and its translocation from bone surfaces to the bone volume caused by bone growth and turnover processes were measured. Average radiation doses and dose rates as a function of age at exposure were determined. Initial uptake and retention, skeletal nuclide concentration, proliferative activity of local cell populations and residence time of the nuclide on skeletal surfaces were affected significantly by age at exposure. The effect of these parameters on tumor induction is discussed. This study has provided early retention and distribution data which together with data from a chronic toxicity study will be used to estimate the risk of Pu exposure relative to that of Ra to humans of all ages.
Aging↗
Effects of spaceflight on trabecular bone in rats.
Alterations in trabecular bone were observed in growing male Wistar rats after 18.5 days of orbital flight on the COSMOS 1129 biosatellite. Spaceflight induced a decreased mass of mineralized tissue and an increased fat content of the bone marrow in the proximal tibial and humeral metaphyses. The osteoblast population appeared to decline immediately adjacent to the growth cartilage-metaphyseal junction, but osteoclast numbers were unchanged. These results suggested that bone formation may have been inhibited during spaceflight, but resorption remained constant. With the exception of trabecular bone mass in the proximal tibia, the observed skeletal changes returned to normal during a 29-day postflight period.
Animals↗
A quantitative histologic study of bone turnover in young adult beagles.
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Age Factors↗
Role of vitamin D in maternal skeletal changes during pregnancy and lactation: a histomorphometric study.
The effect of vitamin D on bone changes during the reproductive cycle in female rats has been investigated. One group of female rats was maintained on a vitamin D-deficient diet and another group of a vitamin D-replete diet from weaning. Both groups were mated with normal males and changes in their bones were determined histomorphometrically during pregnancy, lactation, and after weaning. All vitamin D-deficient rats had bone changes typical of rickets. Pregnancy caused significant reductions in mineralized tissue of trabecular and cortical bone in the vitamin D-deficient rats. Lactation caused further significant reductions in mineralized tissues of cortical and trabecular bone in both the vitamin D-deficient and vitamin D-replete animals, with the greatest changes seen at weaning. Some restoration of mineralized tissues occurred following weaning. There was an increase in tetracycline-labeled bone surface in the vitamin D-replete animals during lactation, likely due to an increase in bone formation rates. In the vitamin D-deficient animals during lactation, there was a decrease in tetracycline-labeled bone surface, likely due to severely depressed bone mineralization. These results indicate that the mobilization of calcium from bone to maintain pregnancy and lactation occurs by a mechanism independent of vitamin D.
Animals↗
Trabecular bone structural variation in biopsy sites of the beagle ilium.
Iliac trabecular bone sites were studied in 2 male and 2 female adult beagles to determine normal structural variability among different sites, and to identify transilial biopsy sites with minimum structural variation. Only sites that provided adequate amounts of trabecular bone were studied. Trabecular bone area and perimeter were measured on microradiographs of ground sagittal sections using a Quantimet 720 image analyzer, and percent bone, perimeter to area ratio, and mean trabecular width were calculated. Over 100% variation was found in the parameters studies among sections from different sites within the same animal. However, variability was minimal among sections obtained more than 2 mm from the lateral or medial cortex within the most caudal sites evaluated. Two sites appropriate for sampling with an 8 mm trephine were identified as being centered over the following points: (a) a point 7 mm caudal to the cranial dorsal spine and 7 mm ventral to the tuber sacrale, and (b) a point 7 mm caudal to the cranial ventral spine and 7 mm dorsal to the tuber coxae. Comparison of data obtained from males and females indicated that sampling variation may also be reduced by using dogs of one sex and by preferential use of males.
Animals↗