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Biomedical subjects

R B Martin

Publications and source records attributed to R B Martin.

174 records · Page 10Linked to original sources
PubMed1965

Exchange of carbon-bound hydrogen atoms ortho to the hydroxyl group in tyrosine.

The carbon-bound hydrogen atoms of tyrosine that exchange with solvent protons in strongly acid solutions at about 100 degrees C are not the methylene hydrogen atoms but a pair on the aromatic ring. Of the two pairs of protons on the aromatic ring, observed in the proton magnetic resonance spectra, the pair at higher field undergoes exchange in 2.4N DCI at 100 degrees C. Other hydrogen atoms, attached either to aliphatic or aromatic carbon atoms, exhibit no noticeable exchange under the same conditions. From a chemicalshift analysis the exchanging protons are assigned as those ortho to the hydroxyl group on the aromatic ring.

Catalysis↗
PubMedDate not supplied

Calculating the probability that microcracks initiate resorption spaces.

This paper explores the assumptions and limitations of the probability calculation that led to the conclusion by Burr et al. (1985) that microcracks initiate new remodeling events. It also corrects several minor errors in the calculation in the original manuscript. The results show that the probability that cracks and resorption spaces are associated depends heavily on a factor, F, that accounts for the possibility that some osteons that contain both a crack and a resorption space share a cement line with an adjacent osteon to which the crack more properly 'belongs.' F in turn depends on (1) the measurement criteria for cracks and resorption spaces, (2) the osteon population density in the bone, and (3) the mechanism by which cracks initiate remodeling. The theoretical maximum number of osteons that can contain both a crack and a resorption space (nmax) increases as the number of resorption spaces (r), the number of cracks (c), and F increase, but decreases as the osteon population density (d) increases. A larger nmax makes a direct association between cracks and resorption spaces more difficult to demonstrate experimentally.

Animals↗
PubMedDate not supplied

Citrate binding of Al3+ and Fe3+.

Citrate occurs at about 0.1 mM in blood plasma and is the most likely small molecule plasma binder of both Al3+ and Fe3+. This paper assesses published stability constants for citrate binding to each metal ion. From pH 2 to 5 Al3+ forms a neutral complex with citrate that may be absorbed into the body in the upper regions of the gastrointestinal tract. It is especially dangerous to ingest aluminum-containing antacids with citrus fruit or juices. Ignoring the likely occurrence of a competing 2:1 citrate-Fe3+ complex necessitates adjustments in reported stability constants for Fe3+ binding to transferrin. In the blood, plasma transferrin steals both Fe3+ and Al3+ from citrate.

Aluminum↗
PubMedDate not supplied

On the histologic measurement of osteonal BMU activation frequency.

When cortical bone is remodeled by osteonal basic multicellular units (BMUs), activation frequency is defined as the number of new BMUs created per unit volume of cortex per unit time. When osteonal remodeling is histomorphometrically analyzed, a different definition of activation frequency is usually used; it is equivalent to the number of previously activated BMUs reaching the plane of the section per unit area per unit time. Using simple geometric analysis, it is shown that the latter histologic measurement is equal to the former definition multiplied by the mean distance that a BMU tunnels before it ceases its activity.

Animals↗
PubMedDate not supplied

New insights into the propagation of fatigue damage in cortical bone using confocal microscopy and chelating fluorochromes.

Fatigue damage in bone occurs in the form of microcracks and plays an important role in the initiation of bone remodelling and in the occurrence of stress and fragility fractures. The process by which fatigue microcracks in bone initiate and grow remains poorly understood. The aim of this study was to investigate the microscopic tissue changes associated with microcracks during crack propagation in cortical bone and the influence of bone microstructure on this process. Cracks were mechanically initiated and extended longitudinally in a two-stage process, in six bovine tibial compact tension specimens. The sequential application of chelating fluorochromes, xylenol orange followed by calcein, allowed the nature of microcrack damage at different stages of propagation to be monitored by laser scanning confocal microscopy. Specimens were imaged at a focal plane 20 microm below the samples' surface, or as a series of z-plane images collected to a maximal depth of 200 microm and 35 microm for x 4 and x 40 objectives, respectively. Z-series image stacks were then reconstructed using Amira 3.0 software. Confocal images showed that xylenol orange localised to the crack surface and did not migrate into the crack's extension following further mechanical propagation. Similarly, calcein stained the extended crack's surface and displayed minimal incorporation within the original crack. High resolution confocal images provided a detailed visual description of the crack's 'process zone', and 'process zone wake'. Additionally, an 'interface region' was revealed, displaying a clear distinction between the end of the first crack and the commencement of its extension. Confocal images of the interface region demonstrated that the extended crack forms a continuum with the pre-existing crack and propagates through the former process zone. Upon viewing the three-dimensional reconstructed images, we found evidence suggesting a submicroscopic tissue involvement in fatigue damage, in addition to the potential influence of vascular canals and osteocyte lacunae on its propagation through the bone matrix. This study has provided new insights into the process of fatigue damage growth in bone and factors influencing its progression through the bone matrix. Confocal microscopy in combination with sequential chelating fluorochrome labelling is a valuable technique for monitoring microcrack growth in bone.

Animals↗
PubMedDate not supplied

Effects of different commercial diets on several orthopedic experiments.

In experiments involving disuse osteoporosis induced by plaster cast immobilization, 2 commonly used commercial feeds (Wayne Lab Blox and Purina Laboratory Chow) gave different results. Preliminary evidence suggests that this dichotomy of results is due to an interaction between metabolic changes caused by physiologic stress and different levels of manganese in the 2 commercial diets. By feeding the 2 diets to groups of rats under various conditions, and examining the strength, cortical area, and length of their femurs, and by immobilization of a fracture in a cast, and associated physiologic stresses, dietary differences are manifested in the growth and developmental changes in the femur. Under normal, stress-free conditions, however, no such differences occur. Investigators should be wary of such dietary variables when comparing various experimental results. The implications of such effects insofar as human medicine is concerned should be further investigated.

Animal Nutritional Physiological Phenomena↗