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Biomedical subjects

D W Dempster

Publications and source records attributed to D W Dempster.

At least 73 records · Page 4Linked to original sources
PubMed1989

Bone resorption by isolated human osteoclasts in vitro: effects of calcitonin.

Human osteoclasts were isolated from 12- to 17-week-old fetal tissue and from transiliac crest bone biopsies for an in vitro study of their biology. A hypodermic needle was used to flush either the fetal long bones or the trabeculae of the iliac crest bone biopsy with tissue culture medium and the resulting cell suspension sedimented briefly either onto the surface of plastic tissue culture dishes, for time-lapse microcinematography, or onto slices of devitalized bovine cortical bone for quantitative assay of bone resorption. The osteoclasts were motile, tartrate-resistant acid phosphatase positive and capable of excavating pits in slices of devitalized bovine cortical bone. Human calcitonin, at doses of 1 ng/ml and 1 microgram/ml, caused a 70% inhibition of bone resorption by human fetal osteoclasts over a 24 h period but had no apparent effect on the morphology or motility of either fetal or adult osteoclasts.

Aging↗
PubMed1989

Skeletal disease in primary hyperparathyroidism.

Most patients with primary hyperparathyroidism in the 1980s do not have evidence of bone disease when they are evaluated by conventional radiography. We sought to determine whether skeletal involvement can be appreciated when more sensitive techniques, such as bone densitometry and bone biopsy, are utilized. We investigated 52 patients with primary hyperparathyroidism. They had mild hypercalcemia, 2.8 +/- 0.03 mmol/liter (11.1 +/- 0.1 mg/dl), low normal phosphorus, 0.9 +/- 0.03 mmol/liter (2.8 +/- 0.1 mg/dl), and no symptoms or specific radiological signs of skeletal involvement. The greatest reduction in bone mineral density was found at the site of predominantly cortical bone, the radius (0.54 +/- 0.1 g/cm; 79 +/- 2% of expected), whereas the site of predominantly cancellous bone, the lumbar spine (1.07 +/- 0.03 g/cm2), was normal (95 +/- 3% of expected). The site of mixed composition, the femoral neck (0.78 +/- 0.14 g/cm2), gave an intermediate value (89 +/- 2% of expected). Preferential involvement of cortical bone with apparent preservation of cancellous bone in primary hyperparathyroidism was confirmed by percutaneous bone biopsy. Over 80% of patients had a mean cortical width below the expected mean, whereas cancellous bone volume in over 80% of patients was above the expected mean. The results indicate that the majority of patients with asymptomatic primary hyperparathyroidism have evidence by bone densitometry and bone biopsy for cortical bone disease. The results also indicate that the mild hyperparathyroid state may be protective of cancellous bone. The therapeutic implications of these observations await further longitudinal experience with this study population.

Biopsy↗
PubMed1988

Interaction of calcium nutrition and physical activity on bone mass in young women.

We have examined the relationships among calcium intake, mechanical stress (activity) and axial (lumbar) and peripheral (midradius) bone mass in a population of 60 young normal, healthy eumenorrheic women (age 25-34 years), selected on the basis of weight for height (within 20% of expected). In this population, vertebral bone mineral density was significantly related (r = 0.41, p less than 0.005) to activity pattern but not to calcium intake. Elimination of the effects of activity, however, disclosed a significant correlation between total calcium intake and vertebral bone mass (r = 0.36, p less than 0.02). Closer examination of this relationship suggested that vertebral bone mineral density did not appear to increase with calcium intakes above 800-1000 mg/day, implying a threshold effect and vertebral density was better expressed as a function of the logarithm of calcium intake (r = p less than 0.01). Radial mineral content was not related to activity (which was mostly walking and running), but it was significantly affected by calcium intake. These data suggest that skeletal status in the vertebrae in young women may be influenced by modulation of mechanical stress. However, bone mineral density is probably also dependent on nutritional status such that the optimum calcium intake for this effect is 800-1000 mg/day. If such effects, observed here cross-sectionally, can be substantiated in longitudinal studies and persist into the aging postmenopausal population, then the average age of onset of osteoporotic fractures would be expected to be delayed approximately 10 years, by relatively simple modifications of diet and activity.

Adult↗
PubMed1988

Trabecular architecture in iliac crest bone biopsies: infra-individual variability in structural parameters and changes with age.

A histomorphometric study was conducted on bilateral iliac crest samples obtained at autopsy from 27 subjects who had died suddenly. Six parameters related to cancellous bone structure were measured: bone volume (BV/TV), surface density (BS/TV), surface/volume ratio (BS/BV), trabecular thickness (Tb.Th.), trabecular number (Tb.N), and trabecular separation (Tb.Sp). There were no significant differences between right and left sides in the mean values for each parameter. However, when subjects were considered individually, there was a substantial difference in the majority of cases for all parameters. The intra-individual variation (IIV) was calculated for each subject as the percentage deviation from the mean for the two sides. There was a wide range in IIV (0.05-30.27%) with a mean value of approximately 11.5% for each parameter. In males the mean IIV ranged from 9 to 11% and from 14 to 16% in females. The IIV in BV/TV was positively correlated with age. Data generated on a subsample of 15 males were used to predict patient group sizes required to detect minimum significant differences in studies involving repeat biopsies. Sample sizes of 32, 16, and 8 patients would be required for relative increments in BV/TV of 29, 36, and 46%, respectively, to be statistically significant. Tb.Sp increased significantly with age but there was no significant change in Tb.Th. This supports the view that bone loss with aging occurs primarily through a mechanism involving complete disappearance of individual trabecular plates.

Adult↗
PubMed1988

Immunocytochemical localization of the 1,25-dihydroxyvitamin D3 receptor in target cells.

We have used a monoclonal antibody (9A7) against the purified avian 1,25-dihydroxyvitamin D3 receptor to develop an immunocytochemical technique for visualization of the protein in fixed tissues and cultured cells. In Bouin's-fixed, chick intestine, 1,25-dihydroxyvitamin D3 receptor-like immunoreactivity was localized mainly in nuclei of epithelial cells and was more abundant in the crypt than in the villar cells. Receptor staining was low or undetectable in liver hepatocytes but was present in nuclei of cells lining the hepatic sinusoids. In rat brain, receptor-like immunoreactivity was abundant and widely distributed, but did not always coincide with the presence of vitamin D-dependent calcium-binding protein; 1,25-dihydroxyvitamin D3 receptor was absent from cerebellar Purkinje cells that contained abundant calcium-binding protein. In disaggregated rat bone cells, receptor immunoreactivity was present in mononuclear cells including osteoblasts and fibroblasts but was absent from osteoclasts. Two separate clones of osteoblast-like, rat osteosarcoma cells, shown in previous studies to be either receptor positive (17/2.8) or negative (24.1), demonstrated nuclear immunoreactivity in exact concordance with receptor levels as determined by ligand binding. The phenomenon of hormone-induced up-regulation of receptor was visualized in receptor-positive 3T6 fibroblasts by demonstration of markedly enhanced nuclear reactivity in cells treated with 10(-7) M 1,25-dihydroxyvitamin D3 for 48 h. Our studies demonstrate the feasibility of the immunocytochemical approach to visualize the 1,25-dihydroxyvitamin D3 receptor in target tissues and show that it is predominantly a nuclear protein in the relatively unoccupied and fully activated states. Moreover, the vitamin D-dependent calcium binding is not a universal marker for 1,25-dihydroxyvitamin D3 action. Rather, our observations suggest that the expression of the 1,25-dihydroxyvitamin D3 receptor may be connected with the state of cellular differentiation.

Animals↗
PubMed1987

Biological activity of chicken calcitonin: effects on neonatal rat and embryonic chick osteoclasts.

Chicken calcitonin (cCT) has recently been synthesized according to nucleotide sequence data. We have investigated the in vitro effects of this hormone on the activity of disaggregated, neonatal rat and embryonic chick osteoclasts. While synthetic cCT inhibited bone resorption by neonatal rat osteoclasts at concentrations as low as 0.1 pg/ml, it failed to produce a significant reduction in bone resorption by embryonic chick osteoclasts, even at concentrations as high as 1 microgram/ml. Similarly, cCT at 1 pg/ml reproducibly produced the rapid and dramatic inhibition of rat osteoclast motility characteristic of other calcitonins, as judged by time-lapse video recording, but did not impair the motile behavior of chick osteoclasts at concentrations up to a million-fold higher. Previous studies showing that embryonic chick osteoclasts were unresponsive to synthetic salmon calcitonin left open the possibility that the native hormone was required to produce an inhibitory effect. We conclude that the osteoclast is not a target cell for calcitonin in the embryonic chick; further studies will be required to define a role, if any, for this potent but enigmatic hormone in birds.

Animals↗
PubMed1987

Tumor-induced osteomalacia. Kinetics of calcium, phosphorus, and vitamin D metabolism and characteristics of bone histomorphometry.

A patient with a mesenchymal tumor and hypophosphatemic osteomalacia was studied before and after tumor excision. Initial laboratory values included normal serum calcium, decreased serum phosphorus and tubular reabsorption of phosphate, undetectable 1,25-dihydroxyvitamin D, and normal parathyroid hormone. Histomorphometry of a bone biopsy specimen showed evidence of increased osteoclastic bone resorption. By 16 hours after tumor removal, 1,25-dihydroxyvitamin D level had normalized, but serum phosphorus level was unchanged; at 28 hours, both serum phosphorus value and tubular reabsorption of phosphate were within normal limits. It is concluded that tumor removal is associated with rapid correction both of 1,25-dihydroxyvitamin D production and of renal phosphate wasting. Increased bone resorption suggests the production of an osteoclast activator by the tumor and may explain the typically normal serum calcium value in this disorder.

Adult↗
PubMed1987

A comparative study of disaggregated chick and rat osteoclasts in vitro: effects of calcitonin and prostaglandins.

Disaggregated chick osteoclasts sedimented onto bovine cortical bone slices excavate deep and sharply defined resorption lacunae that stain intensely with toluidine blue. We have used this observation to develop a simple light microscopic method for quantifying the bone resorptive activity of chick osteoclasts in vitro. Using this technique, we have found that disaggregated chick osteoclasts are strikingly less sensitive than rat osteoclasts to salmon calcitonin (sCT). Bone resorption by rat osteoclasts was completely abolished by synthetic sCT at a concentration of 10 pg/ml. In contrast, sCT at concentrations up to 100 micrograms/ml did not significantly inhibit bone resorption by chick osteoclasts. Bone resorption by chick osteoclasts could, however, be inhibited by prostaglandin E2 at concentrations of 10(-6) M or more. In time-lapse video experiments, the motility of rat osteoclasts was rapidly inhibited by sCT (5-50 pg/ml), prostaglandins I2 and E2 (less than or equal to 10(-4) M), and Bu2cAMP (2.5 X 10(-4) M), whereas chick osteoclasts failed to show such a response. These findings suggest that CT does not play an important role in the regulation of osteoclastic activity in the chick and may explain why injection of the hormone has generally not been found to evoke an acute hypocalcemic response in birds. This fundamental difference in response to CT may limit the utility of chick osteoclast systems as models of mammalian bone resorption.

Animals↗
PubMed1986

On the role of seizure activity in the hippocampal damage produced by trimethyltin.

Trimethyltin (TMT) causes a pattern of hippocampal damage in rats that is similar to that caused by convulsant chemicals or seen in the brains of some human epileptics. Therefore, we investigated the possible role that TMT-induced seizure activity might play in the hippocampal damage produced by this organotin. The morphologic effects of systemically administered TMT were compared to those of kainic acid given by the same route. Unlike kainate, TMT produced seizures in only a subset of treated animals and with a latency of days rather than minutes. Evaluation of morphology during the acute seizure period revealed that TMT-induced seizures were associated with a variable pattern of granule and pyramidal cell necrosis and acute dendritic swelling in the two associational/commissural hippocampal pathways, one from CA3 to CA1-CA3 and the other from the hilus to the proximal dendrites of dentate granule cells. The TMT-induced damage contrasted sharply with the acute pattern of kainate-induced damage that consisted of acute dendritic swellings in the distal granule cell dendrites, hilus and mossy fiber region. TMT-treated rats that did not exhibit seizures in the one week after injection exhibited minimal pathology during this period. These results suggest that at least part of the damage to granule and pyramidal cells produced by TMT is mediated by the seizure activity produced by this compound. Although the resulting lesions to the CA1-CA3 pyramidal cells may appear similar in both TMT- and kainate-treated rats long after injection, evaluation of acute pathology during the active seizure phase indicates that these compounds induce seizure activity in different hippocampal pathways and cause different patterns of irreversible neuronal damage as a result.

Animals↗
PubMed1986

A simple method for correlative light and scanning electron microscopy of human iliac crest bone biopsies: qualitative observations in normal and osteoporotic subjects.

Despite the fact that the scanning electron microscope (SEM) offers a number of unique advantages for the investigation of bone structure, this instrument has seldom been applied in studies of the iliac crest bone biopsy. Here we describe a very simple method of preparing iliac crest biopsies for examination in the SEM after the routine histomorphometric analysis has been performed. With observations on biopsies from normal subjects and patients with osteoporosis, the paper illustrates the potential of the method for performing correlative light and scanning electron microscopical studies and for gaining new information on the three-dimensional architecture of trabecular bone.

Biopsy↗
PubMed1986

The effect of oral phosphate administration on major indices of skeletal metabolism in normal subjects.

The effect of brief periods of phosphate administration on indices of human skeletal metabolism was investigated. Thirteen subjects (8 women, 5 men; 19-36 years old) received 2 g of oral phosphate daily for 5 days. Serum phosphorus rose 26% (3.8 +/- 0.1 mg/dl to 4.8 +/- 0.1 mg/dl; p less than .01) while total calcium fell (9.3 +/- 0.1 mg/dl to 8.9 +/- 0.1 mg/dl; p less than .01). Parathyroid hormone levels increased by 50% (14.1 +/- 2.0 pg/ml to 21.5 +/- 1.7 pg/ml; p less than .05) although values remained within the normal range. A persistent phosphaturia (0.64 +/- 0.10 g/g Cr to 1.8 +/- 0.4 g/g Cr; p less than .05) and a 69% fall in urinary calcium (80.8 +/- 10.0 mg/g Cr to 24.6 +/- 6.0 mg/g Cr; p less than .001) were observed. 1,25-dihydroxyvitamin D3 and urinary hydroxyproline concentrations did not change significantly but the bone gamma-carboxyglutamic acid protein (BGP) concentration rose 41% by day 2 (9.6 +/- 1.3 mg/ml to 13.5 +/- 2.2 mg/ml; p less than .005) and remained elevated throughout the study period. These results support the possibility that brief periods of phosphate administration may be useful in the therapy of disorders associated with low bone turnover, such as osteoporosis.

Administration, Oral↗
PubMed1986

Bone vitamin D-dependent calcium-binding protein is localized in chondrocytes of growth-plate cartilage.

The cellular distribution of vitamin D-dependent calcium-binding protein (CaBP) was examined in rat and chicken bone by immunocytochemical methods using an antiserum raised against purified chicken intestinal CaBP. In EDTA-decalcified, Vibratome sections of growing rat long bones, specific CaBP immunostaining was observed in cytoplasm of chondrocytes of the growth plate, particularly in regions of calcification. In undecalcified, frozen sections from neonatal rat, positive staining was seen in chondrocytes of tibial growth plate and also in chondrocytes of the long bones of the skull. No specific immunostaining was observed in osteoblasts, osteocytes or osteoclasts in mineralized bone. In frozen sections of tibias from 19-day-old chick embryos specific immunostaining was again confined to dividing chondrocytes of the growth plate and was much less intense in "resting" cartilage. The finding of CaBP in chondrocytes, cells known to possess specific receptors for 1,25-dihydroxyvitamin D3 and to respond to the hormone, suggests a possible functional role for CaBP in chondrocyte maturation, differentiation and/or cartilage calcification.

Animals↗
PubMed1986

Effect of pH on bone resorption by rat osteoclasts in vitro.

Acidosis has been implicated in the pathogenesis of various metabolic bone diseases. Experimental acid ingestion is known to stimulate the release of bone mineral in humans and increase osteoclastic resorption surfaces in animals, but the mechanism has remained unclear. We have investigated the effect of medium pH on osteoclastic activity in vitro using a new method that allows direct measurement of bone resorption. Osteoclasts were disaggregated from neonatal rat long bones and allowed to settle onto thin slices of bovine cortical bone. After 24-h incubation in medium 199, adjusted to the required pH, bone slices were fixed, and the number and surface area of resorption pits per slice were determined. Reduction in medium pH from 7.4 to 6.8 resulted in a 14-fold increase in the mean area resorbed per bone slice (P less than 0.01). Five- and 9-fold increases were seen at pH 7.2 and 7.0, respectively. Incubation of bone cells with human PTH-(1-34) (100 ng/ml) did not significantly enhance resorption at either pH 7.4 or 6.4, whereas human calcitonin (50 pg/ml) produced near-total inhibition. Mean osteoclast and mononuclear cell numbers were unaltered by all treatments. This is the first direct demonstration that low pH stimulates cell-mediated bone resorption, an observation that may have considerable physiological and pathophysiological significance.

Acidosis↗
PubMed1985

"Epileptic" brain damage is replicated qualitatively in the rat hippocampus by central injection of glutamate or aspartate but not by GABA or acetylcholine.

Repeated intraventricular injection of the excitatory amino acids glutamate and aspartate for one hour produced morphologic changes in the hippocampus that were qualitatively identical to the acute and chronic changes seen in the brains of human epileptics and in experimental animals in which hippocampal seizure activity was induced by kainic acid or electrical stimulation of the perforant path. Light and electron microscopy revealed acute effects of glutamate and aspartate consisting of glial and dendritic swelling and neuronal soma necrosis ("dark cell degeneration"). Electron microscopy showed the focal dendritic swelling induced by glutamate or aspartate to be of the axon-sparing type with presynaptic terminals relatively unaffected. Four weeks after injection, irreversible neuron loss and reactive gliosis had occurred. The inhibitory amino acid gamma-aminobutyric acid caused acute glial swelling similar to that caused by glutamate and aspartate but did not produce neurotoxic effects, indicating that glial swelling may not be causally related to neuronal death but may be the result of amino acid uptake. The excitatory non-amino acid acetylcholine produced no direct, periventricular hippocampal damage or glial swelling but did produce dendritic swelling in the CA3 region innervated by the perforant path, presumably as a result of acetylcholine-induced seizure activity in this pathway. Glutamate and aspartate also caused glial and neuronal changes in other periventricular structures, e.g., septum, hypothalamus, caudate and habenula, as well as in the most dorsal portion of the cerebellum. Dendritic swelling induced by glutamate and aspartate in the cerebellar molecular layer was accompanied by acute necrosis of Purkinje cell somata. These results suggest that seizure-associated brain damage is initiated by excessive endogenous excitatory amino acid receptor activation.

Acetylcholine↗
PubMed1984

Cellular and mitochondrial changes induced in the structure of murine skeletal muscle by crotoxin, a neurotoxic phospholipase A2 complex.

Following a single i.m. injection of a sublethal dose of crotoxin into the hindlimb of mice, degenerative changes were observed in the soleus muscle in the ensuing 72 hr using light and electron microscopy. A similar degree of myonecrosis resulted from the injection of the phospholipase A2 subunit alone, whereas crotoxin reconstituted from a chemically modified phospholipase A2 subunit with low catalytic activity showed weak myonecrosis and the non-enzymic subunit, crotapotin, was inactive. Visible defects of the sarcolemma were associated with underlying necrotic areas and attraction of macrophages. Internally, hypercontraction bands were often present and mitochondria in the rounded, orthodox configurational state contained linear dark bodies as part of their crystal organization. In fibre segments with slow onset of degeneration, many mitochondria additionally contained clusters of electron opaque deposit and in mitochondria, heavily laden with such deposits, energy-dispersive microprobe analysis showed the presence of high concentration of calcium. It was concluded that the primary site of action of crotoxin was hydrolysis of the sarcolemmal membrane and that mitochondrial changes were associated with calcium accumulation in response to an altered internal environment. Regeneration of fibres was rapid.

Animals↗
PubMed1983

Mean wall thickness and formation periods of trabecular bone packets in corticosteroid-induced osteoporosis.

We have compared the mean wall thickness (MWT) and active formation periods (sigma f(A] of trabecular bone packets in iliac crest biopsies from 20 patients (7 male, 13 female) with corticosteroid-induced osteoporosis (CS-OP) and 20 age- and sex-matched controls. The trabecular bone volume (TBV) of the CS-OP patients (9.6% +/- 2.2% [SD]) was significantly reduced compared to controls (19.3% +/- 5.1%). The MWT of CS-OP patients (32.7 +/- 4.3 micron) was also significantly lower than the control value (48.0 +/- 6.2 micron). There was a positive correlation between MWT and TBV in both groups. The mineralization rate (M) of the CS-OP patients (0.54 +/- 0.25 micron/day) was within the normal range, and since there was no increase in osteoid seam thickness, so therefore was the osteoblastic appositional rate (OAR). The active formation period of trabecular bone packets (sigma f(A) = MWT/M) was significantly lower in the CS-OP patients (55.9 +/- 14.4 days) than in the control group (68.1 +/- 9.4 days). MWT and sigma f(A) both decreased with age in the control group, whereas in the CS-OP group they were independent of age. We conclude that corticosteroid therapy results in a reduction of the MWT of trabecular bone packets and, consequently, of TBV. In these patients, where the OAR was normal, the reduction in MWT was apparently caused by a shortening of the life-span of the active osteoblastic population at the basic multicellular unit (BMU) level.

Adrenal Cortex Hormones↗