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Biomedical subjects

C Robinson

Publications and source records attributed to C Robinson.

At least 325 records · Page 18Linked to original sources
PubMed1989

Interaction of neuropeptides with human mast cells.

Mast cells of human skin, but not lung, adenoids, tonsils, or intestine, release histamine in response to substance P, vasoactive intestinal polypeptide, and somatostatin. The substance P receptor of skin mast cells is not of the NK-1, NK-2 or NK-3 subtypes of smooth muscle. Time course and calcium dependency of release by peptides differed from anti-IgE. With anti-IgE, the molar ratios of histamine:PGD2:LTC4 generated by skin mast cells was 1,000:25:2, whereas with substance P these ratios were 1,000:1:0.1. Similar results were obtained with the other neuropeptides. The ability of peptides to stimulate skin mast cell histamine release suggests a mechanism whereby their release from dermal nerve endings is coupled to changes in microvasculature.

Histamine Release↗
PubMed1989

Retention of glucose in oral fluid at different sites in the mouth.

Using glucose as a marker, a detailed study of retention at 5 different sites in the mouth of 1 subject and a less detailed examination of 4 selected sites in the mouths of 10 other subjects revealed site-specific differential patterns of oral retention (or clearance). These patterns seemed independent of sometimes large, absolute day-to-day variations in oral retention which occur in all subjects but appeared to vary somewhat between subjects, probably reflecting slight differences in the anatomy and physiology of the individual mouth. In general, the patterns resembled those recently derived from studies of other oral phenomena such as rates of diffusion out of plaque, fluoride uptake by mineral and hydrogen ion concentrations in plaque. They will dictate the concentrations and thereby influence the activity of all extraneous substances in different regions of the oral cavity and may relate to the site-specific patterns of oral disease.

Administration, Oral↗
PubMed1989

A microbiological study of early caries of approximal surfaces in schoolchildren.

A cross-sectional epidemiological study has been undertaken to relate the bacterial composition of approximal dental plaque with the earliest stages of caries development in schoolchildren. Small samples of plaque were removed from multiple sites around the contact areas of 42 premolars extracted for orthodontic reasons from 29 schoolchildren (mean age = 13.5 yr). Caries diagnosis was based on polarized light microscopy and contact microradiography of thin sections cut through the sample sites. Fifty-seven percent of sites (37/60) showed histological evidence of demineralization. Both the isolation frequency and the mean percentage viable count of mutans streptococci and Actinomyces viscosus were higher at sites with early caries, although mutans streptococci could not be detected at 37% of sites with early caries. At these latter sites, the proportions of Veillonella were markedly reduced. Lactobacilli were rarely isolated and were never recovered from caries-free surfaces. Analysis of the data shows that the relationship between plaque bacteria and enamel is neither merely passive nor indifferent, and that particular stages of lesion formation may be associated with different combinations of bacteria.

Adolescent↗
PubMed1989

The IgE- and calcium-dependent release of eicosanoids and histamine from human purified cutaneous mast cells.

Cells dispersed from human foreskin were passively sensitized with IgE and then depleted or enriched in mast cells by density gradient centrifugation. Arachidonic acid metabolism was initially studied by radio-high-performance liquid chromatography analysis of incubation media from cells that had been prelabeled with [3H] arachidonic acid. In subsequent experiments with unlabeled cells the eicosanoids were quantified by radioimmunoassay. Prostaglandin (PG)D2 was the major cyclooxygenase product released from purified mast cells challenged with anti-IgE or A23187. In density gradient studies there was a significant correlation between PGD2 and histamine release (r = 0.52, p less than 0.01) and between PGD2 release and the numbers of mast cells (r = 0.42, p less than 0.02). There was no correlation with the total numbers of nucleated cells. Other cyclooxygenase products were also detected, the formation of 6-keto-PGF1 alpha and PGE2 being principally associated with gradient fractions containing endothelial cells. Leukotriene (LT)C4 was the major lipoxygenase product detected, reaching a maximum of 3.87 +/- 0.56 ng/10(6) mast cells upon activation with anti-IgE compared with 35.37 +/- 7.22 ng/10(6) mast cells of PGD2. When normalized to histamine release and expressed in molar terms, skin mast cells released approximately 20-fold more PGD2 than LTC4. Thus, the cutaneous mast cell is one likely source of the PGD2 and LTC4 released during cutaneous immediate hypersensitivity reactions.

Antibodies↗
PubMed1989

Control of crystal growth during enamel maturation.

Attempts to promote crystal growth in maturation stage enamel from rat incisors were carried out by incubation in saturated solutions of calcium phosphate. Resulting crystallites were visualised in the TEM and the dimensions of their profiles measured. No crystal growth was observed unless the maturation stage enamel was first pretreated with either 8M urea or sodium hypochlorite to remove residual protein matrix. The results suggest that the protein matrix plays an important role in the control of crystal growth in vivo.

Animals↗
PubMed1989

The enamelin/non-amelogenin problem. A brief review.

Non-amelogenin components can be isolated from enamel, these may be 1. True enamel components (more than one)? (a) Discrete protein(s). (b) Composite polypeptide, amelogenin/non-amelogenin, alternative splicing. (c) Stable physical complex, amelogenin/non-amelogenin aggregate. 2. Albumin/serum protein from circulation? 3. Keratin - (a) New secretory type? (b) Ameloblast cytoskeletal proteins embedded in matrix. 4. Actin - Ameloblast cytoskeleton embedded in matrix. 5. Enzymes (proteolytic, dephosphorylating).

Amelogenin↗
PubMed1988

Transport of proteins into chloroplasts. Organization, orientation, and lateral distribution of the plastocyanin processing peptidase in the thylakoid network.

Plastocyanin is synthesized in the cytoplasm as a larger precursor and transported into the thylakoid lumen of the chloroplast. Maturation of preplastocyanin involves successive cleavages by a stromal peptidase and a distinct thylakoidal peptidase. In this report we have analyzed the precise location and orientation of the thylakoidal peptidase with respect to the thylakoid membrane. Experiments involving differential centrifugation of thylakoid extracts and sonication of isolated vesicles indicate that the peptidase is tightly bound to the thylakoid membrane but not intimately associated with any of the major thylakoid protein complexes. Analysis of the lateral distribution of the peptidase has shown that the enzyme is exclusively located in the non-appressed lamellae of the thylakoid network. The active site of the peptidase is on the lumenal face of the thylakoid membrane.

Chloroplasts↗
PubMed1988

The metabolism of prostaglandin D2 after inhalation or intravenous infusion in normal men.

Tritium-labelled prostaglandin D2 (PGD2) was administered to normal volunteers by either intravenous infusion or inhalation in order to establish which metabolites of PGD2 are initially found in human plasma. Inhaled PGD2 was rapidly absorbed from the airways, as indicated by the rapid appearance of tritium in the plasma. Metabolites chromatographically similar to 9 alpha,11 beta-PGF2 and 13,14-dihydro-15-keto-9 alpha,11 beta-PGF2 were found after both routes of administration. At later time points, other unidentified compounds were present. Only after intravenous infusion was there evidence of metabolites with 9 alpha,11 alpha stereochemistry of the ring hydroxyl functions. In human lung, 9 alpha,11 beta-PGF2 was metabolized in the presence of NAD+ to compounds tentatively identified by gas chromatography/mass spectrometry (GC/MS) as 15-keto-9 alpha,11 beta-PGF2 and 13,14-dihydro-15-keto-9 alpha,11 beta-PGF2. Thus, after 11-ketoreductase-dependent metabolism of PGD2 to the biologically active compound 9 alpha,11 beta-PGF2, further metabolism probably proceeds by the combined action of 15-hydroxyprostaglandin dehydrogenase/15-ketoprostaglandin-delta 13-reductase (15-PGDH/delta 13R). Both 9 alpha,11 beta-PGF2 and its 13,14-dihydro-15-keto metabolite may be useful analytes for the measurement of PGD2 turnover, and may therefore prove to be important in understanding the pathophysiological significance of this putative mediator.

Administration, Inhalation↗
PubMed1988

Organ selective conversion of prostaglandin D2 to 9 alpha, 11 beta-prostaglandin F2 and its subsequent metabolism in rat, rabbit and guinea pig.

Cell-free 100,000 g supernatants from liver, kidney, lung and caecum of rat, rabbit and guinea-pig were compared for their ability to transform prostaglandins F2 alpha, D2, E2 and 9 alpha, 11 beta-prostaglandin F2 (11epi-PGF 2 alpha) to metabolic products. Experiments utilized multitritiated substrate PGs, with assessment of biotransformation by TLC, HPLC and GC/MS. PGF2 alpha was converted via the sulphasalazine analogue-inhibitable NAD+-dependent 15-hydroxy-prostaglandin dehydrogenase pathway (15-PGDH), with high activity (greater than 5 pmol/min/mg protein) in all 12 systems except rat and rabbit liver (e.g. guinea-pig kidney and rat caecum both 64 pmol/min/mg; rat liver 0.3 pmol/min/mg), forming 15-keto and 13,14-dihydro-15-keto metabolites as determined by TLC, HPLC and GC/MS. Prostaglandin D2 was not transformed in similar fashion in NAD+- or NADP+-supplemented incubations in any of the 12 cytosolic systems. However, PGD2 was converted to a single product identified by TLC, HPLC and GC/MS as 9 alpha, 11 beta-PGF2 in certain of the systems when supplemented with an NADPH regenerating system, with high activity in guinea-pig kidney (55.0 pmol/min/mg), guinea-pig liver (27.5 pmol/min/mg) and rabbit liver (13.7 pmol/min/mg) and less than 5 pmol/min/mg in 8 of the remaining 9 systems. This stereospecific 11-ketoreductase of rabbit and guinea-pig liver was stable to 10 min heating at 50 degrees, dialysis, storage at -20 degrees and repeated freeze/thawing but was not inhibited by sulphasalazine analogues. The 11-ketoreductase had a markedly different tissue profile from PGE2 9-ketoreductase, which was shown to convert PGE2 stereospecifically to 9 alpha, 11 alpha-prostaglandin F2 (PGF2 alpha) and was present at highest activity in rabbit liver and kidney. Evidence was obtained that 9 alpha, 11 beta-PGF2 was actively transformed by the sulphasalazine-inhitable 15-PGDH pathway at approximately one third of the rate of PGF2 alpha with high activity in several cytosolic systems (e.g. rat caecum, guinea-pig liver and kidney), suggesting that further transformation in vivo of this biologically active product of PGD2 metabolism could be initiated by this route.

Animals↗
PubMed1988

Relationship between enamel formation and eruption rate in rat mandibular incisors.

The relationship between the formation of dental enamel and tooth eruption was investigated. Rat mandibular incisor eruption rate was accelerated by maintaining incisors out of occlusion. Rate of eruption, enamel thickness, secretory zone length and matrix breakdown were measured. Eruption rate increased by 120% in experimental teeth but enamel secretion increased by only 90%. There were no obvious differences between control and experimental teeth in final enamel thickness or in the molecular weight distribution of the enamel matrix proteins.

Animals↗
PubMed1988

Site-specific differences in human dental plaque pH after sucrose rinsing.

The object was to find out whether site-specific variations of pH might correlate with those of oral clearance as indicated by past studies using fluoride, sucrose and glucose as markers. Eleven subjects with 24 h growth of dental plaque rinsed the mouth with a 10% solution of sucrose. The pH of plaque, harvested from the labial or buccal cervical and approximal regions of certain teeth or groups of teeth, was then measured. The results confirmed previous reports that plaque pH varies from site to site in the mouth; the pattern observed was similar in each of the subjects. In the anterior part of the mouth, concentrations of hydrogen ion were invariably higher in plaque from the upper than from the lower surfaces of the teeth. The reverse pattern was found in the posterior part. This site-specific pattern was similar to that of oral clearance, as indicated by comparison with known values for glucose concentrations, a finding consistent with the view that site-specific pattern of plaque pH may reflect or at least be influenced by such differential clearance patterns.

Adolescent↗
PubMed1988

Volume distribution and concentration of protein, mineral and water in developing bovine enamel.

The percentage volume of enamel occupied by mineral, matrix protein and water was determined at each of four stages. Protein decreased throughout development from 20 to 30 per cent to a minimum of 2-3 per cent in mature tissue. Mineral content remained fairly consistent during secretion (15-20%) rising to 70-80 per cent in mature enamel. Water content rose from varying levels to 60-70 per cent at the secretion/maturation boundary decreasing to about 20 per cent in mature enamel. The loss of protein and subsequent delay in the onset of mineral increment resulted in tissue porosity. The duration of this hydrated, porous stage may determine susceptibility of the tissue to, for example, fluoride ion.

Animals↗
PubMed1988

Distribution of fluoride in the enamel of rat incisors examined by an abrasive microsampling technique.

This study was undertaken to reveal detailed changes in fluoride distribution at different developmental stages of upper incisor enamel under various fluoride administration regimes. Four groups of Wistar rats received water containing 0, 25, 50 and 100 parts/10(6) fluoride respectively for 10 weeks. Five different enamel specimens were removed from the developing enamel, excluding the matrix-formation stage. Fluoride distribution in each specimen was analysed from the surface to the enamel-dentine junction using an abrasive microsampling technique. Fluoride concentration was invariably highest at the surface and decreased sharply towards the interior at every site in both control and experimental groups. The concentration throughout the tissue increased with fluoride intake at each stage of development. The fluoride-gradient curves were similar at each of the different sites of tooth development. However, the fluoride concentration of the enamel interior was significantly higher at early maturation than at the other four sites.

Animals↗