Biomedical subjects

B M Bowman

Publications and source records attributed to B M Bowman.

8 recordsLinked to original sources

PubMed1992

Differences in cortical bone in overloaded and underloaded femurs from ovariectomized rats: comparison of bone morphometry with torsional testing.

Osteopenia and mechanical incompetence are the defining features of osteoporosis, yet the effects of changes in bone structure on mechanical properties are not completely understood. The primary objective of this study was to determine if in a rodent model, changes in cortical bone structure, as measured by static morphometry, would correlate with functional properties, as measured by torsional testing. For this, cortical bone structure and stiffness were determined in overloaded and underloaded limbs in rats rendered ovarian hormone-deficient by ovariectomy (OVX). Rats were OVX and six weeks later a hind limb was immobilized by casting for an additional six weeks. In all cases the femur from the underloaded, casted limb was compared with that from the contralateral, overloaded limb. The success of this experimental protocol was confirmed by differences in femoral cancellous bone volume by microradiography and single photon absorptiometry, with the overloaded limb having a greater bone volume and bone mineral density than the contralateral, immobilized controls. Morphometric differences in the femoral diaphyseal cortical bone included greater endocortical perimeter and endocortical osteoclast surface, less cortical area, less minimum cortical width, and less minimum cortical width at fracture planes when the bones were tested for stiffness in the underloaded, compared with the contralateral, overloaded limbs. Using a torsional test, the ultimate torque to failure and stiffness were less in the underloaded femurs compared with the contralateral, overloaded femurs. These results emphasize the importance of mechanical loading on bones from a gonad-deficient animal.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Calcium absorption and osseous organ-, tissue-, and envelope-specific changes following ovariectomy in rats.

Because cancellous bone loss occurs following ovariectomy (OVX) in rats, this has become a popular model to explore therapeutic modalities for postmenopausal bone loss in humans. The purpose of this study was to determine intestinal calcium absorption in situ and organ-, tissue-, envelope-, and site-specific changes in osseous tissues at six weeks after OVX in rats using chemical, biochemical, absorptiometric, microradiographic, and morphometric methods. There were no changes in intestinal absorption of calcium, but duodenal weight per length was significantly increased in the OVX animals compared with age-matched, sham-operated controls. There was an increase in wet bone weight, but decreases in ash/dry bone weight, total bone Ca, and Ca per ash weight in the OVX animals. There were significant decreases in the OVX animals in metaphyseal bone mineral content, as determined by photon absorptiometry and metaphyseal cancellous bone volume. The perimeter to area ratio of the metaphyseal cancellous bone in the OVX animals was increased compared with controls. Endochondral growth rates were increased in the OVX animals, attributable to an increased growth plate hypertrophic cell size and rate of chondrocyte proliferation. In the OVX animals there was an increase in modeling in the formation mode of the periosteal surface at the tibio-fibular junction. Increased periosteal modeling in the formation mode was also observed in the body of the mandible, suggesting that the changes in periosteal bone formation are not strictly coupled with changes in endochondral growth. There was an increase in modeling in the resorption mode of the endocortical surface at the tibio-fibular junction in the OVX animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗

PubMed1989

Ultrastructural features of osteoclasts in situ.

The morphology of in situ osteoclasts on endocortical surfaces of the femoral midshaft was examined by scanning electron microscopy. Mice were perfusion fixed and bone marrow plugs were flushed out of femoral diaphyseal cylinders. The bones were split longitudinally and the endocortical surfaces examined. This method left on the bone surface most of the endosteal cells in their natural, in situ shape and position. Most of the bone surface was lined by contiguous bone lining cells covering resting bone surfaces, making a clear physical barrier between the bone and marrow compartments. On resorption surfaces, which were characterized by excavation cavities, osteoclasts were very polymorphic and spread on the bone surface, extending large pseudopods. The in vivo morphology of individual osteoclasts appears somewhat similar to that described by other investigators on calvaria surfaces and for isolated osteoclasts adherent to artificial substrates. In the resorption domains, osteoclasts appeared to be connected with adjacent osteoclasts, suggesting that the cells form a functional syncytium in resorption areas.

Animals↗

PubMed1989

Bone lining cells: structure and function.

Bone lining cells (BLC's) cover inactive (nonremodeling) bone surfaces, particularly evident in the adult skeleton. BLC's are thinly extended over bone surfaces, have flat or slightly ovoid nuclei, connect to other BLC's via gap junctions, and send cell processes into surface canaliculi. BLC's can be induced to proliferate and differentiate into osteogenic cells and may represent a source of "determined" osteogenic precursors. BLC's and other cells of the endosteal tissues may be an integral part of the marrow stromal system and have important functions in hematopoiesis, perhaps by controlling the inductive microenvironment. Because activation of bone remodeling occurs on inactive bone surfaces, BLC's may be involved in the propagation of the activation signal that initiates bone resorption and bone remodeling. Evidence also suggests that BLC's are important in the maintenance of the bone fluids and the fluxes of ions between the bone fluid and interstitial fluid compartments for mineral homeostasis.

Animals↗

PubMed1988

Chromosome 18 allele loss at the D18S6 locus in human colorectal carcinomas.

This is the first report of chromosome 18 allele loss in colorectal carcinomas from FAP patients and concurrent allele losses on chromosomes 5 and 18 in sporadic colorectal cancer. This is based on our investigation of twenty-two colorectal carcinomas from sporadic cases and FAP patients which revealed tumor-specific allele loss of at least 44% at the D18S6 locus on chromosome 18 in informative cases. These results coupled with the tentative assignment of an HNPCC gene to chromosome 18 suggests that a gene on chromosome 18 may be involved in the etiology of some colon cancers. Possible mechanisms involving genetic changes on chromosome 18 in colon cancer are discussed in relation to tumor- or growth-suppressor genes.

Alleles↗

PubMed1986

The proliferation and differentiation of the bone-lining cell in estrogen-induced osteogenesis.

The purpose of this study was to determine the capacity of the bone-lining cell, which covers most nonremodeling bone surfaces in the adult skeleton, to proliferate and contribute to the rapid endosteal osteogenic response following estrogen treatment in male Japanese quail. In control, untreated birds bone-lining cells cover most of the femoral endosteal surface. Bone-lining cells are thinly extended along bone surfaces, have flat nuclei, and account for about 77% of the cells adjacent to the bone surface. The lineal density of bone surface cells in the controls was about 21 cells/mm of bone surface. By 16-20 h after estrogen administration cells with larger, round nuclei were seen on the bone surface and some of these cells contained a 3H-thymidine (3H-TdR) label. Within the first 24 h after estrogen administration the lineal bone surface cell density had increased to about 38 cells/mm. At 20-30 h after estrogen administration, most of the cells adjacent to the bone surface were round. The peak 3H-TdR labeling of cells immediately adjacent to the bone surface occurred about 36 h after estrogen administration. By 48 h the bone surface was covered with osteogenic cells and developing medullary bone. These results suggest that the bone-lining cell in the adult appears to retain some proliferative capability and osteogenic potential. However, because a rapid increase in cell density began prior to the rapid increases in 3H-TdR labeling, as well as the appearance of mitotic figures on the bone surface, another source of cells may have also contributed to the osteogenic response induced by estrogen.

Animals↗

PubMed1985

Distributions of cell populations within alpha-particle range of plutonium deposits in the rat and beagle testis.

Plutonium is not uniformly distributed in testicular tissues; thus some cell populations may receive larger or smaller radiation exposures than would be expected if the nuclide were uniformly distributed. The distributions of cell populations within alpha-particle range of Pu deposits in rat and beagle testes were determined. The data were collected from autoradiographs of testicular tissues containing 241Pu. A cell distribution factor (CDF) was determined for each cell population and is defined as the average number of each cell type within alpha-particle range of each observed Pu deposit relative to the number of each cell type that would be expected within alpha-particle range of each Pu deposit, if the deposits were distributed uniformly. In addition, the percentage of the spermatogonial stem cell population within alpha-particle range of Pu deposits was determined. In rats, the CDF for the spermatogonial stem cells is about 2.2. This value is similar to other enhancement and inhomogeneity factors reported for rodents in the literature. In beagles the CDFs to all cells in the seminiferous epithelium were less than the rats. In addition, the percentage of spermatogonial cells within alpha-particle range of Pu concentrations in the interstitial tissues was a factor of about 3 less in the dog than in the rat. The largest CDFs seen in both species were in the interstitial tissues, particularly for Leydig cells. Because the organization of testicular tissues in the beagle is quite different from rodents but more similar to human, the results from this study suggest that extrapolations from rodents to humans may tend to overestimate the potential for radiation exposure to spermatogonial stem cells as well as the fraction of the spermatogonial stem cell population at risk to exposure from internally deposited 239Pu.

Alpha Particles↗

PubMed1978

Prediction of head/neck dynamic response of selected military subjects to -Gx acceleration.

Eighteen young male subjects with NAMRL sled test experience to 15 G in --Gx acceleration were measured for physical characteristics of the head and neck and general body anthropometry. Measurements taken include head/neck range of motion, neck muscle stretch reflex time, neck muscle isometric strength capabilities, and seated and standard anthropometry. Data from these tests were tabulated and five subjects whose physical characteristics were most similar were selected for use in simulations. Experimental data from NAMRL sled tests were obtained for the five subjects in 6- and 15-G test runs. Measurements data from the five subjects were used to establish a data set for the MVMA-2D Crash Victim Simulator and acceleration profiles for 6- and 15-G sled runs were used as input to the model. Simulation results for head angular acceleration, head angular velocity, head angular position, head resultant acceleration, and T1 resultant acceleration were compared with the averaged experimental curves for the five subjects. In general, excellent agreement between simulation and experimental results was obtained although some consistent differences were noted. Effects of varying levels of muscle activation were investigated. Variations in muscle tension level were found to have significant effects on simulation results at both 6 and 15, G, especially on head angular position. The effects were noticeably greater at lower acceleration's, however. The model was also used to investigate some of the biomechanical mechanisms behind observed response characteristics.

Acceleration↗