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Biomedical subjects

A Duncan

Publications and source records attributed to A Duncan.

At least 55 records · Page 3Linked to original sources
PubMed1997

Effect of diets varying in nitrogen or phosphorus content on indicators of bone growth in lambs.

Growing lambs were fed diets low in nitrogen and phosphorus (LNLP), low in nitrogen and high in phosphorus (LNHP), high in nitrogen and low in phosphorus (HNLP) or high in nitrogen and phosphorus (HNHP) and the effects on bone growth and on blood and urinary bone marker levels or excretion rates were monitored. Plasma calcium concentrations were higher, and phosphorus concentrations lower, in lambs fed the low phosphorus diets but there were no differences in plasma 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) concentrations. Lambs fed both low phosphorus diets (LNLP and HNLP) had lower plasma osteocalcin and higher bone-specific alkaline phosphatase concentrations than those fed the high phosphorus diets. Urinary pyridinoline and deoxypyridinoline excretion were also affected by treatment, with their rates of excretion being highest in lambs fed the diet low in both nitrogen and phosphorus (LNLP). Lambs fed the low phosphorus diets were lighter in weight at slaughter and had lighter bones that were less well mineralized than those fed the high phosphorus diets. Reducing the nitrogen content of the diet appeared to have little effect on bone composition. These results suggest that bone markers that have proved useful in the diagnosis and treatment of bone disease are sensitive to variation in nutrient supply and may prove useful in early detection of nutrient deficiencies that affect bone growth.

Animals↗
PubMed1996

Distribution and quantification of pyridinium cross-links of collagen within the different maturational zones of the chick growth plate.

In order to assess alterations in the collagen network during endochondral ossification the pyridinium cross-links of collagen were quantified in sequential transverse sections through the chick growth plate. This was accomplished using both morphological (alkaline phosphatase (ALP) histochemistry and collagen type X immunostaining) and analytical (HPLC) analyses. In articular cartilage, pyridinoline concentrations were maximal in the deep mature zones. In contrast, the proliferating chondrocyte zone of the growth plate had approximately a 10-fold greater pyridinoline cross-link concentration than the mature hypertrophic zone. Deoxypyridinoline was first found in the prehypertrophic zone of the growth plate cartilage that reacted positively for ALP activity but before collagen type X was detected. However, deoxypyridinoline concentrations were highest in the most differentiated regions of the growth plate where it was the principal pyridinium cross-link. In tibial dyschondroplasia, where chondrocyte differentiation is arrested in the prehypertrophic zone, higher concentrations of both cross-links were found with increasing distance down the lesion. We conclude that the decrease in pyridinoline cross-link concentration down the growth plate may be an essential adaptation (via increased collagenase activity and collagen turnover) of the matrix for vascular invasion and osteoclastic resorption to occur.

Animals↗
PubMed1996

Effect on lipoprotein profile of replacing butter with margarine in a low fat diet: randomised crossover study with hypercholesterolaemic subjects.

OBJECTIVE: To examine the effect on lipid and lipoprotein concentrations when butter or an unsaturated margarine is used for cooking or spreading in a reduced fat diet. DESIGN: Randomised crossover study with two intervention periods of six weeks' duration separated by a five week washout. SETTING: Community setting in New Zealand. SUBJECTS: 49 volunteers with polygenic hypercholesterolaemia and baseline total cholesterol concentration in the range 5.5-7.9 mmol/l. MAIN OUTCOME MEASURES: Concentrations of total and low density lipoprotein, Lp(a) lipoprotein, high density lipoprotein, apolipoprotein B 100, and apolipoprotein A I. RESULTS: Concentrations of low density lipoprotein cholesterol and apolipoprotein B were about 10% lower with margarine than with butter. Lp(a) lipoprotein and high density lipoprotein cholesterol concentrations were similar with the two diets. CONCLUSION: Despite concerns about adverse effects on lipoproteins of trans fatty acids in margarines, the use of unsaturated margarine rather than butter by hypercholesterolaemic people is associated with a lipoprotein profile that would be expected to reduce cardiovascular risk.

Apolipoprotein A-I↗
PubMed1996

Transfer of horseradish peroxidase from oligodendrocyte to axon in the myelinating neonatal rat optic nerve: artefact or transcellular exchange?

In this paper we make the surprising observation that intracellular injection of horseradish peroxidase (HRP) into a single myelinating oligodendrocyte also resulted in localised HRP labelling at the nodes of Ranvier of some axons of the unit. It appeared that HRP had been transferred to the nodal axoplasm from the paranodal loops of the HRP-filled oligodendrocyte. Three HRP-filled oligodendrocytes from isolated optic nerves of 14-day-old rats were analysed by serial section electron microscopy, and HRP was observed in the axonal cytoplasm at three of the nodes of Ranvier delineated by one of the cells. At labelled nodes, HRP was of a uniform intensity throughout the nodal axoplasm. Axonal labelling gradually diminished along the paranodal regions and was not evident in the contiguous internodal axoplasm beyond 20 microns from the node. The myelin sheaths, paranodal loops, and axons appeared normal at labelled nodes, and the paranodal loops and astrocyte perinodal processes adjacent to those of the HRP-filled oligodendrocyte unit did not contain HRP. There was no evidence of extracellular HRP or tissue damage in the surrounding neuropil, and axons neighbouring those enwrapped by the HRP-filled oligodendrocyte did not contain HRP. The possibility that axonal labelling was an artefact of either iontophoretic injection or tissue preparation is discussed. This provocative finding is not definite proof of exchange, but the balance of evidence supports the possibility that there was transcellular exchange of HRP at paranodes between the labelled oligodendrocyte and some of the axons in the unit. The rarity of HRP transfer to axons suggests that it may be a transient or labile event. It is not clear whether oligodendrocyte to axon macromolecular exchange has real physiological and/or pathological significance.

Animals↗
PubMed1996

Limiting time-unlimited group psychotherapy.

For a number of reasons, we decided to bring three long-term, open-ended psychodynamic therapy groups to termination. We examine the process that began with the announcement of the change to a time-limited format, and concluded with the termination of the group. The transition had a powerful impact on the members and the group-as-a-whole. The therapists used supervision to deal with the intensity of the group process and the countertransference demands posed by the transition. Groups facing a similar change due to economic pressures may benefit from these observations.

Adult↗
PubMed1996

Measurement of cranial optical path length as a function of age using phase resolved near infrared spectroscopy.

Near infrared spectroscopy (NIRS) has been used to measure concentration changes of cerebral hemoglobin and cytochrome in neonates, children, and adults, to study cerebral oxygenation and hemodynamics. To derive quantitative concentration changes from measurements of light attenuation, the optical path length must be known. This is obtained by multiplying the source/ detector separation by a laboratory measured differential path length factor (DPF) which accounts for the increased distance traveled by light due to scattering. DPF has been measured by time of flight techniques on small populations of adults and postmortem infants. The values for adults are greater than those for newborns, and it is not clear how to interpolate the present data for studies on children. Recent developments in instrumentation using phase resolved spectroscopy techniques have produced a bedside unit which can measure optical path length on any subject. We have developed an intensity modulated optical spectrometer which measures path length at four wavelengths. Two hundred and eighty three subjects from 1 d of age to 50 y were studied. Measurements were made at a fixed frequency of 200 MHz and a source detector separation of 4.5 cm. Results suggest a slowly varying age dependence of DPF, following the relation DPF690 = 5.38 + 0.049A0.877, DPF744 = 5.11 + 0.106A0.723, DPF807 = 4.99 + 0.067A0.814, and DPF832 = 4.67 + 0.062A0.819, where DPF690 is the DPF measured at 690 nm and A is age is expressed in years from full term. There was a wide scatter of values, however, implying that ideally DPF should be measured at the time of each study.

Adolescent↗
PubMed1996

Technetium-99m-HMPAO labelled leucocytes in the detection and monitoring of inflammatory bowel disease in children.

This study was a retrospective evaluation of the use of technetium-99m hexamethylpropyleneamineoxime (HMPAO) labelled leucocytes in the investigation of suspected inflammatory bowel disease in children. The images were analysed in 35 children and the findings were compared with the results of endoscopy/biopsy, barium studies and antinuclear cytoplasm antibody (ANCA) serology. The sensitivity of the white cell scan was 83% and the specificity 81%. This compares well with other studies in adults and is superior to barium investigations. The technique is recommended as a first line investigation to detect inflammatory bowel disease with a resultant reduction in the use of endoscopy and barium imaging.

Adolescent↗
PubMed1996

Measurement of sugar probes in serum: an alternative to urine measurement in intestinal permeability testing.

The percentage dose of lactulose and mannitol excreted in urine after oral ingestion is used as a noninvasive method of assessing small intestinal permeability. The collection of incomplete or inaccurately timed urine samples can lead to errors in estimation of sugar probe molecules. We describe an HPLC method for the simultaneous determination of lactulose and mannitol in serum after oral ingestion of test sugars. We applied the test to healthy volunteers and to subjects undergoing jejunal biopsy for suspected gluten-sensitive enteropathy. The ratio of concentrations of lactulose and mannitol in serum discriminated well between subjects with a normal biopsy and those with villous atrophy, discrimination being best at 90 min postdose. The results agree well with lactulose:mannitol ratios determined in urine (r= 0.88), and the two methods can be used interchangeably. The determination of mannitol and lactulose in serum provides an acceptable alternative to urine collection and may be particularly useful in young children. It also reduces the time spent on the investigation from 5 h to 90 min.

Biopsy↗
PubMed1996

Clastogenic effects of defined numbers of 3.2 MeV alpha particles on individual CHO-K1 cells.

Research to determine the effects of defined numbers of alpha particles on individual mammalian cells is helpful in understanding risks associated with exposure to radon. This paper reports the first biological data generated using the single-particle/single-cell irradiation system developed at Pacific Northwest Laboratory. Using this apparatus, CHO-K1 cells were exposed to controlled numbers of 3.2 MeV alpha particles, and biological responses of individual cells to these irradiations were quantified. Chromosomal damage, measured by the induction of micronuclei, was evaluated after no, one, two, three or five particle traversals. Exposures of up to five alpha particles had no influence on the total numbers of cells recovered for scoring. With increased numbers of alpha particles there was a decrease in the ratio of binucleated to mononucleated cells of 3.5%/hit, suggesting that alpha particles induced dose-dependent mitotic delay. A linear hit-response relationship was observed for micronucleus induction: Micronuclei/binucleated cell = 0.013 +/- 0.036 + (0.08 +/- 0.013) x D, where D is the number of particles. When the estimated dose per alpha-particle traversal was related to the frequency of induced micronuclei, the amount of chromosomal damage per unit dose was found to be similar to that resulting from exposures to alpha particles from other types of sources. Approximately 72% of the cells exposed to five alpha particles yield no micronuclei, suggesting the potential for differential sensitivity in the cell population. Additional studies are needed to control biological variables such as stage of the cell cycle and physical parameters to ensure that each cell scored received the same number of nuclear traversals.

Alpha Particles↗
PubMed1996

Enzyme-linked immunosorbent assay for thrombin-antithrombin III complexes in horses.

OBJECTIVES: To adapt and characterize a human ELISA kit to quantify thrombin-antithrombin III (TAT) complexes in horses, and to evaluate TAT as a marker for hypercoagulation in horses. ANIMALS: 29 clinically normal horses used as controls, and 4 ill horses used to evaluate assay for known causes of hypercoagulation. PROCEDURE: A commercially available human sandwich-type ELISA kit with 2 antibodies against human thrombin and antithrombin III that bind selectively to their corresponding TAT antigenic sites was used. Equine TAT standards were made from purified equine thrombin and antithrombin III. Proteins diluted in a phosphate-buffered saline solution containing 0.1% Tween and 1 U of heparin/ ml were used to establish standard curves. Reference intervals for TAT concentration in citrated equine plasma, and intra- and interassay coefficients of variation were determined. RESULTS: Mean +/- SD values were 3.95 +/- 1.93 micrograms/L, with median of 3.18 micrograms/L and range of 1.95 to 9.03 micrograms/ L. One horse with cecal perforation had TAT concentration of 174.30 micrograms/L, and a horse infused IV with endotoxin had TAT concentration of 62.98 micrograms/L 12 hours after infusion. CONCLUSIONS: The data suggest that human TAT ELISA kits can be used to measure TAT concentration in citrated equine plasma, and that TAT is a marker for hypercoagulation in horses. CLINICAL RELEVANCE: Assays for equine TAT many help to further characterize the hypercoagulable state in horses.

Animals↗
PubMed1996

Standardization of pyridinium crosslinks, pyridinoline and deoxypyridinoline, for use as biochemical markers of collagen degradation.

The collagen crosslinks, pyridinoline and deoxypyridinoline, have been developed as urinary markers of bone resorption but, despite wide clinical application of the technique, comparatively little attention has been paid to the standardization of these compounds. In this study, pyridinoline and deoxypyridinoline have been purified from bone and converted completely to monochloride trihydrochloride salts. In addition to mass spectrometry and NMR spectroscopy, the purity of the isolated materials was assessed by microelemental analysis including the chloride counterions. These purified compounds were used to establish individual molar absorptivity values as primary standardization criteria for the two crosslinks. For pyridinoline in 0.1 mol/L HCl, epsilon at 295 nm was 5490 L mol(-1) cm(-1); in 50 mmol/L sodium phosphate, pH 7.5, epsilon at 325 nm was 5785. The corresponding values for deoxypyridinoline at acid and neutral pH were 5160 and 5290 L mol(-1) cm(-1). The availability of standardization criteria for the crosslinks will allow more meaningful comparisons of clinical data between different laboratories.

Amino Acids↗
PubMed1995

Predicted complementarity determining regions of the T cell antigen receptor determine antigen specificity.

The antigen receptor on T cells (TCR) has been predicted to have a structure similar to a membrane-anchored form of an immunoglobulin F(ab) fragment. Virtually all of the conserved amino acids that are important for inter- and intramolecular interactions in the VH-VL pair are also conserved in the TCR V alpha and V beta chains. A molecular model of the TCR has been constructed by homology and we have used the information from this, as well as the earlier structural predictions of others, to study the basis for specificity. Specifically, regions of a TCR cloned from an antigen-specific T cell were stitched into the corresponding framework of a second TCR. Results indicate that the substitution of amino acid sequences corresponding to the complementarity determining regions (CDRs) of immunoglobulin can convey the specificity for antigen and major histocompatibility complex molecules. These data are consistent with a role, but not an exclusive role, for CDR3 in antigen peptide recognition.

Amino Acid Sequence↗
PubMed1995

Axon-glial relationships in the anterior medullary velum of the adult rat.

The anterior medullary velum is a thin sheet of CNS tissue which roofs the rostral part of the IVth ventricle and contains fascicles of myelinated fibres which, in part, arise from the nucleus of the IVth cranial nerve. This study used histochemical, immunohistochemical, and intracellular dye-injection techniques to describe cellular interrelationships in the velum in whole-mounts and in sections. Rip antibody-stained whole mounts provided a unique description of both oligodendrocyte units (defined as an oligodendrocyte and the complement of myelinated internodal segments it forms), and consecutive myelin sheaths along the same axon. A broad range of unit morphologies was categorised into four arbitrary groups, according to classical criteria, which comprised small cells supporting the short, thin myelin sheaths of 15-30 small diameter axons (Type I), through intermediate types (II & III), to the largest cells forming the long, thick myelin sheaths of 1-3 large diameter axons. Rip antibody and ferric ion-ferrocyanide staining, together with intracellular dye injection, revealed oligodendrocyte process branching patterns and their mode of engagement of myelin sheaths, nodes of Ranvier, and the spatial disposition of the outer cytoplasmic rims of myelin sheaths. The latter formed a conspicuous spiral ridge on the exterior surface of myelin sheaths which connected with the paranodal loops at each heminode. Large bundles of axons decussated through the velum, the bulk of which were IVth nerve fibres which constituted the IVth nerve rootlet. The PNS/CNS transitional zone of the IVth nerve was located 0.25-0.50 mm along the root, where astrocytic end-feet defined an abrupt margin, convex towards the periphery, where the heminodes of central and peripheral myelin were apposed, and where the basal lamina tubes of the Schwann cell units were discontinued. The basal processes of ependymal cells lining the ventricular wall of the velum, passed between axon bundles before abutting on the basal lamina of the pia. Many of these processes branched and ran along the axonal bundles. A monolayer of microglia occupied a subependymal stratum in which the non-overlapping dendritic territories of each cell formed a regular mosaic throughout the velum without any obvious interaction with either axons or other glial cells. Astrocytes were also uniformly distributed; their fine processes made up a dense lattice amongst axons, often running parallel and within the fibre bundles; stouter ones had terminal end-feet which undercoated the basal lamina of both the glia limitans externa and the blood vessels in the velum.

Animals↗
PubMed1995

Optical pathlength measurements on adult head, calf and forearm and the head of the newborn infant using phase resolved optical spectroscopy.

We have used an intensity modulated optical spectrometer, which measures the phase shift across tissue experienced by intensity modulated near-infrared light, to determine the absolute optical pathlength through tissue. The instrument is portable and takes only 5 s to record pathlength at four wavelengths (690 nm, 744 nm, 807 nm and 832 nm). The absolute pathlength divided by the known spacing between the light source and detector on the skin is the differential pathlength factor (DPF) which previous studies have shown is approximately constant for spacings greater than 2.5 cm. DPF results are presented for measurements on 100 adults and 35 newborn infants to determine the statistical variation on the DPF. All measurements were made at a frequency of 200 MHz with source-detector spacings of > 4 cm. Results at 807 nm show a DPF of 4.16(+/- 18.8%) for adult arm, 5.51(+/- 18%) for adult leg, 6.26(+/- 14.1%) for adult head and 4.99(+/- 9%) for the head of a newborn infant. A wavelength dependence was obtained for DPF on all tissues and a difference in DPF between male and female was observed for both the adult arm and leg. The results can be used to improve the quantitation of chromophore concentration changes in adults and newborn infants.

Adult↗