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Biomedical subjects

R Armstrong

Publications and source records attributed to R Armstrong.

At least 73 records · Page 4Linked to original sources
PubMed1992

In vivo measurements of lead in bone at four anatomical sites: long term occupational and consequent endogenous exposure.

Measurements of bone lead concentrations in the tibia, wrist, sternum, and calcaneus were performed in vivo by x ray fluorescence on active and retired lead workers from two acid battery factories, office personnel in the two factories under study, and control subjects. Altogether 171 persons were included. Lead concentrations in the tibia and ulna (representative of cortical bone) appeared to behave similarly with respect to time but the ulnar measurement was much less precise. In an analogous fashion, lead in the calcaneus and sternum (representative of trabecular bone) behaved in the same way, but sternal measurement was less precise. Groups occupationally exposed to lead were well separated from the office workers and the controls on the basis of calculated skeletal lead burdens, whereas the differences in blood lead concentrations were not as great, suggesting that the use of concentrations of lead in blood might seriously underestimate lead body burden. The exposures encountered in the study were modest, however. The mean blood lead value among active lead workers was 1.45 mumol l-1 and the mean tibial lead concentration 21.1 micrograms (g bone mineral)-1. The kinetics of lead in the tibia appeared to be noticeably different from that in the calcaneus. Tibial lead concentration increased consistently both as a function of intensity of exposure and of duration of exposure. Calcaneal lead concentration, by contrast, was strongly dependent on the intensity rather than duration of exposure. This indicated that the biological half life of lead in calcaneus was less than the seven to eight year periods into which the duration of exposure was split. Findings for retired workers clearly showed that endogenous exposure to lead arising from skeletal burdens accumulated over a working lifetime can easily produce the dominant contribution to systemic lead concentrations once occupational exposure has ceased.

Adult↗
PubMed1991

Acitretin plus UVB therapy for psoriasis. Comparisons with placebo plus UVB and acitretin alone.

UVB radiation is beneficial for the treatment of psoriasis vulgaris. Patients with recalcitrant disease, however, are slow to respond to UVB phototherapy with and without the use of coal tars or emollients. Etretinate and, more recently, acitretin have proved useful, but clinical improvement is slow when they are used as monotherapy in plaque psoriasis. Each drug also produces side effects, some of which are dose related. This study was designed to compare results of treatment with UVB combined with either acitretin (50 mg/day) or placebo to determine if psoriasis would respond faster and to less cumulative exposure to UVB and acitretin. The psoriatic disease cleared to a greater degree in patients treated with acitretin-UVB with fewer treatments and smaller amounts of UVB radiation than in patients treated with either placebo-UVB or acitretin alone.

Acitretin↗
PubMed1991

Transforming growth factor-beta 2 enhances the osteoinductive activity of a bovine bone-derived fraction containing bone morphogenetic protein-2 and 3.

We previously identified a novel glycoprotein in an osteoinductive fraction from bovine bone (Bentz et al.: Amino acid sequence of bovine osteoinductive factor. J. Biol. Chem. 265: 5024-5029, 1990). We now find that this fraction also contained small amounts of bone morphogenetic protein-2 and 3 (BMP-2 + 3) previously identified by others (see Wozney, J.M.: Bone morphogenetic proteins. Prog. Growth Factor Res. 1: 267-280, 1990). Separation of BMP-2 + 3 from the glycoprotein was achieved with a modified reversed phase-high pressure liquid chromatographic procedure. When assayed in the rat subcutis using a collagen-ceramic carrier, the osteoinductive activity was found in the subfraction containing BMP-2 + 3. This activity was potentiated and the ratio of cartilage to bone was increased by transforming growth factor-beta 2. The glycoprotein, originally called osteoinductive factor, has been renamed osteoglycin. In its precursor form, osteoglycin is a member of the leucine-rich family of proteins showing the characteristic 24-residue internal homology. Its biological function is unknown.

Amino Acid Sequence↗
PubMed1991

Comparison of a topical mixture of lidocaine and prilocaine (EMLA) versus 1% lidocaine infiltration on wound healing.

We compared a eutectic mixture of lidocaine and prilocaine (EMLA, Astra Pharmaceuticals, Inc) with 1% lidocaine infiltration to determine the effect on wound healing in a prospective single blind study using the rat model. Thirty-six wounds were assessed. No clinical or histologic evidence of infection or necrosis was present in any wound. Five wounds (two in the lidocaine and three in the EMLA group, P = 1.0) demonstrated a widened scar owing to healing by secondary intention following suture disruption. There was no significant difference between groups in the degree of inflammation (P = 0.08). We conclude that EMLA does not affect wound healing adversely and is comparable to 1% lidocaine infiltration in the animal model. Further study to determine its anesthetic effect in laceration repair is presently being undertaken.

Administration, Topical↗
PubMed1990

The cellular and molecular events of central nervous system remyelination.

Central nervous system (CNS)* regeneration is a subject of great interest, particularly in diseases causing a dramatic loss of neurons. However, some CNS diseases do not affect neurons but damage other cells, such as the myelin-forming cells--called oligodendrocytes--which are also crucial to the harmonious function of the nervous system. Diseases in which oligodendrocytes and myelin are attacked can cause devastating neurological dysfunction which is sometimes followed by recovery and myelin repair or remyelination. The question of the regeneration potential of oligodendrocytes in experimental and human demyelinating diseases such as multiple sclerosis has been debated for a long time. Present evidence suggests that oligodendrocyte precursor cells persist in the adult CNS and that oligodendrocyte regeneration can occur but may be limited by ongoing disease processes. Here we will briefly review recent advances which have broadened our understanding of the cellular and molecular events of CNS remyelination.

Age Factors↗
PubMed1990

In vitro analysis of the oligodendrocyte lineage in mice during demyelination and remyelination.

A demyelinating disease induced in C57B1/6N mice by intracranial injection of a coronavirus (murine hepatitis virus strain A59) is followed by functional recovery and efficient CNS myelin repair. To study the biological properties of the cells involved in this repair process, glial cells were isolated and cultured from spinal cords of these young adult mice during demyelination and remyelination. Using three-color immunofluorescence combined with [3H]thymidine autoradiography, we have analyzed the antigenic phenotype and mitotic potential of individual glial cells. We identified oligodendrocytes with an antibody to galactocerebroside, astrocytes with an antibody to glial fibrillary acidic protein, and oligodendrocyte-type 2 astrocyte (O-2A) progenitor cells with the O4 antibody. Cultures from demyelinated tissue differed in several ways from those of age-matched controls: first, the total number of O-2A lineage cells was strikingly increased; second, the O-2A population consisted of a higher proportion of O4-positive astrocytes and cells of mixed oligodendrocyte-astrocyte phenotype; and third, all the cell types within the O-2A lineage showed enhanced proliferation. This proliferation was not further enhanced by adding PDGF, basic fibroblast growth factor (bFGF), or insulin-like growth factor I (IGF-I) to the defined medium. However, bFGF and IGF-I seemed to influence the fate of O-2A lineage cells in cultures of demyelinated tissue. Basic FGF decreased the percentage of cells expressing galactocerebroside. In contrast, IGF-I increased the relative proportion of oligodendrocytes. Thus, O-2A lineage cells from adult mice display greater phenotypic plasticity and enhanced mitotic potential in response to an episode of demyelination. These properties may be linked to the efficient remyelination achieved in this demyelinating disease.

Animals↗
PubMed1990

An improved in vivo neutron activation system for measuring kidney cadmium.

An in vivo neutron activation system for measuring kidney cadmium has been redesigned, firstly to reduce ambient dose levels and, secondly, to improve the cadmium signal to neutron dose ratio by modifying the neutron spectrum from 238Pu/Be, by interposing a beryllium premoderator. The ambient dose was reduced by a factor of seven. The overall system performance (lower limit of detection for a given dose) was improved by 40-50%. This 238Pu/Be based system now performs as well as or better than analogous 252Cf systems, without the drawback of the relatively short half life of 252Cf.

Cadmium↗
PubMed1989

High performance liquid chromatographic measurement of lignocaine in tissue samples following transabdominal placental biopsy.

A method is described for the measurement of lignocaine in small samples of fetal and placental tissue. Tissue samples (ca 100 mg) are digested using a preteolytic enzyme. Lignocaine and an internal standard are extracted into methyl tert-butyl ether and analysed by high-performance liquid chromatography with electrochemical detection (+1.0 V vs Ag/AgCl). The limit of accurate measurement is better than 0.1 mg/kg wet weight for a 100 mg sample. This method has been used to assess fetal exposure to the drug when used as a local anaesthetic during transabdominal placental biopsy (chorionic villus sampling). The range of lignocaine concentrations found in the tissue samples was large (from less than 0.04 mg/kg wet weight to 15.4 mg/kg wet weight) although most samples contained less than 1.0 mg lignocaine/kg wet weight.

Animals↗
PubMed1989

Use of lead aspartate block staining in quantitative EM autoradiography of phospholipids: application to myelinating peripheral nerve.

For quantitation of electron microscope (EM) autoradiographs, micrographs must contain clear images which are relatively free of heavy metal precipitates. Satisfactory contrast is usually obtained by staining individual ultra-thin sections with lead citrate. It was recently reported that sequential block staining of tissue with ferrocyanide-reduced osmium tetroxide and lead aspartate produced excellent contrast for EM autoradiography, with sections relatively free of lead precipitate. This protocol avoids the manipulation involved in staining individual ultra-thin sections. We have adapted this method to quantitative EM autoradiographic studies, primarily of phospholipid metabolism in peripheral nerve. We show that block staining with lead aspartate provides: (a) ultrastructural contrast of routinely high quality for myelinated peripheral nerve; (b) high (greater than 98%) retention of glycero-labeled lipid during dehydration and embedment; and (c) a distribution of de novo tritiated glycerol-labeled lipid in ultra-thin sections that is quantitatively identical to the distribution recorded for samples stained by the more laborious post-embedment method. During a 2-hr labeling period in vivo, tritiated glycerol is incorporated into phosphatidylcholine (44%), phosphatidylethanolamine (22%), other phospholipids (16%), and neutral lipids (15%). The analysis of grain distribution in developing sciatic nerve labeled for 2 hr with tritiated glycerol demonstrates that myelinating Schwann cells play the major role in synthesis of endoneurial lipids. Lipid synthesis in myelinated fibers is localized in perinuclear regions of Schwann cell cytoplasm. These regions lie external to compact myelin. Unmyelinated fibers and other endoneurial cells independently incorporate glycerol into lipids.

Animals↗
PubMed1989

Ambulatory care teams: the dehassling of Air Force medicine.

Lack of complete outpatient medical records is a chronic problem. Most facilities are only able to find 60% to 70% of records for appointments. Many records have incomplete laboratory and x-ray information. A program utilizing Ambulatory Care Teams (ACTS) was tested at the Air Force hospital at Carswell AFB. Records were pulled 48 hours prior to appointments, and the day prior to the appointment clinics endeavored to locate 100% of the records and reports. During a 1-year test period the staff at Carswell was able to produce or account for 98.2% of all medical records for more than 102,000 scheduled appointments.

Aerospace Medicine↗
PubMed1988

Deposition and transfer of axonally transported phospholipids in rat sciatic nerve.

Radioactive glycerol, ethanolamine, or choline injected into the vicinity of the cell bodies of rat sciatic nerve sensory fibers is incorporated into phospholipid. Some newly synthesized ethanolamine and choline phosphoglycerides are subsequently committed to transport down the sciatic nerve axons at a rate of several hundred millimeters per day. Most labeled choline phosphoglycerides move uniformly down the axons; in contrast, the crest of moving ethanolamine phosphoglycerides is continually attenuated. These data, as well as differences in the clearance of these phospholipids distal to a nerve ligature, suggest that various classes of labeled phospholipids are differentially unloaded from the transport vector (possibly by exchange with unlabeled lipid in stationary axonal structures) during movement down the axons. The extent of unloading appears to be defined by the base moiety; both diacyl and plasmalogen species of ethanolamine phosphoglycerides exchange extensively with stationary axonal lipids, while most choline phosphoglycerides continue down the axons. Autoradiographic studies with 3H-choline and 3H-ethanolamine demonstrated that most unloaded phospholipid is initially deposited in axonal structures; some of this unloaded lipid is subsequently transferred to the axon/myelin interface (axolemma?) and then to myelin. Although transported ethanolamine phosphoglycerides exchange more extensively with lipids in stationary axonal structures than do choline phosphoglycerides, at early times more label from 3H-choline is found in myelin. A model to resolve this seeming discrepancy is proposed, wherein a differential topographic localization of phospholipid classes in the membrane of the transport vector allows for a preferential extensive exchange of transported ethanolamine phosphoglycerides with lipids in stationary axonal structures, while choline phosphoglycerides become available for rapid transfer to myelin by a process involving vesicle fusion with axolemma.

Animals↗
PubMed1987

Axonal transport through nodes of Ranvier.

Axonally transported glycoproteins are shown to accumulate at nodes of Ranvier. We hypothesize that the increased labeling in nodal regions results from the rheological effects of axonal constriction as well as from selective deposition of some transported labeled molecules.

Animals↗