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R B Edwards

Publications and source records attributed to R B Edwards.

At least 37 records · Page 2Linked to original sources
PubMed1995

Scintigraphy for diagnosis of avulsions of the origin of the suspensory ligament in horses: 51 cases (1980-1993).

The medical records of 34 horses with a diagnosis of avulsion of the origin of the suspensory ligament that had been admitted to the veterinary medical teaching hospital between 1980 and 1993 were identified. In addition to clinical examination, 21 of 34 horses had scintigraphy and radiography performed during their examination. The usefulness of scintigraphy and radiography were assessed by comparing the initial findings reported in the medical record to those obtained in a retrospective review of the images. Thirty other horses with scintigraphic lesions of the proximal aspect of the third metacarpal/metatarsal bone but with a confirmed diagnosis other than avulsion of the suspensory ligament served as controls for lesion specificity. Scintigraphy (bone phase, n = 21) revealed increased uptake in all horses in both reviews. Only 14 of 21 (67%) horses radiographed, however, had at least 1 lesion during the initial radiographic evaluation that was reported to be suggestive of avulsion. When the radiographs were reviewed retrospectively, the radiologist identified 18 of 21 (86%) horses with lesions consistent with avulsion. The interpretation of scintigraphy appeared to be a more repeatable and sensitive diagnostic method than radiography. However, though scintigraphy was sensitive in identifying inflammation of the proximal aspect of the metacarpal/metatarsal region, no specific diagnosis of avulsion could be made without coincident radiography; the specificity of scintigraphy in diagnosing avulsion of the suspensory ligament was only 41% (21/51).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Evidence of a functional VIP receptor in cultured human retinal pigment epithelium.

The effect of VIP on the intracellular cyclic AMP of human retinal pigment epithelium cultures has been studied. Functional VIP receptor has been demonstrated in cultures from eyes given by five normal donors (age 16-64) (N-HRPE). But it has been found to be absent from high passage number cultures obtained from a retinitis pigmentosa eye of an 84-year-old patient (RP-HRPE). After 3 min of reaction with 1 x 10(-6) M VIP, the intracellular cyclic AMP level has increased to 5-15-fold over the basal level. The maximal effect of VIP (20-fold over the basal level) has been observed at 1 x 10(-7) M VIP. The half maximal activity of VIP is 3-5 x 10(-8) M. The present study also demonstrates the inducibility of the VIP responsiveness in RP-HRPE cultures after they have been treated with butyrate. Curr. Eye Res. 14: 1009-1014, 1995.

Adolescent↗
PubMed1994

Exchange of retinol between IRBP and CRBP.

During a bleach, all-trans-retinol passes from the photoreceptor outer segments to the retinal pigment epithelium (RPE), where retinol is found associated with cellular retinol-binding protein (CRBP). Interphotoreceptor retinoid-binding protein (IRBP) is thought to facilitate this exchange, but the transfer of retinol between IRBP and CRBP has not been explored. In this study we used a mixture of purified IRBP and CRBP as a model system to measure the amount and rate of retinol transfer between the two proteins. When retinol is transferred from IRBP to CRBP, its absorbance maximum shifts from 330 to 350 nm. By monitoring the increase in absorbance at 350 nm after mixing CRBP with IRBP-bound retinol, we measured the amount and time course of retinol transfer from IRBP to CRBP. To complement the absorbance measurements, the IRBP and CRBP in these mixtures were subsequently separated by size-exclusion HPLC and individually analysed for retinol content by scanning the effluent with a multiple-diode-array detector. As determined by measuring the change in absorbance at 350 nm, the mean percentage of IRBP-bound retinol transferred to CRBP was 103 +/- 11% (n = 9). The mean half-time of the transfer was 4.2 +/- 1.3 sec; time to reach equilibrium was 30-60 sec. IRBP that was separated from the mixture by HPLC contained little or no retinol, while the isolated CRBP was nearly saturated with retinol. No detectable transfer from CRBP to IRBP was observed. The distribution of retinol between these two proteins was consistent with the nearly 100-fold higher affinity of CRBP for retinol compared with IRBP. Both the degree and time-course of transfer support the idea that this difference in affinity contributes to the flow of retinol to the RPE during a bleach in vivo and, therefore, may play a role in the physiological regeneration of rhodopsin.

Animals↗
PubMed1993

Adult rabbit brain synthesizes retinoic acid.

Tissues of adult rabbit brain were shown to enzymatically oxidize retinol and retinaldehyde to retinoic acid, a potent stimulator of gene expression. Rates of retinoic acid synthesis by the cerebrum, cerebellum, and meninges were comparable to, or exceeded, rates measured with rat liver, an organ known to have a relatively high capacity to synthesize retinoic acid. These results, taken together with previous observations that the adult brain contains retinoic acid-activated transcription factors and cellular retinoid-binding proteins, suggest that retinoids may play an important role in the adult central nervous system.

Animals↗
PubMed1992

Synthesis of retinoic acid from retinol by cultured rabbit Müller cells.

Previous observations have shown that Müller glial cells of the vertebrate retina contain cellular retinoid-binding proteins, that the retina contains retinoic acid, and that cellular retinoic acid-binding protein is present in amacrine neurons (and, in some species, Müller cells) within the retina. These findings led to the suggestion that Müller cells may synthesize retinoic acid and release it for use by other retinal cells. To test this possibility, we cultured Müller cells from adult rabbit retinas, incubated the cultures with radioactive retinol, and identified and quantified the resultant radioactive retinoids by HPLC. Retinaldehyde was rapidly synthesized from retinol, reaching a plateau of 1-2 pmol mg-1 cell protein by 30 min. Retinoic acid initially accumulated more slowly, but by 30 min constituted most of the synthesized retinoid. While the retinaldehyde remained within the cells, retinoic acid was rapidly released into the medium; extracellular retinoic acid exceeded the intracellular amount after 30 min of incubation. Smaller amounts of retinyl esters were also synthesized and retained by the cells. These results are consistent with the suggestion that Müller glia are a source of retinoic acid in the retina. The synthesis of retinoic acid by these cells, and the presence of retinal neurons that contain cellular retinoic acid-binding protein, raise the possibility that retinoic acid plays a role in the retina, although this role is not presently known. Furthermore, these results may have implications for other parts of the adult nervous system. Adult brain contains retinol- and retinoic acid-binding proteins, and, therefore, may also be a site of retinoic acid metabolism. Because of the relatively simple cellular organization of the retina and its demonstrated capacity to synthesize retinoic acid, the retina may be a system of choice for further studies of the synthesis and function of retinoic acid in adult neural tissue.

Animals↗
PubMed1991

Stimulation of rod outer segment phagocytosis by serum occurs only at the RPE apical surface.

The phagocytosis of isolated rod outer segments by cultured rat retinal pigment epithelium (RPE) previously has been shown to be stimulated by serum in the culture medium. In vivo, serum is normally in contact with the basolateral surface of the RPE. Components of serum have also been detected in the interphotoreceptor matrix, raising the possibility that these components may be in contact with the apical RPE surface. However, with conventional culture techniques it is not clear whether the stimulation of phagocytosis by serum occurs at the basolateral or apical surface. To resolve this uncertainty, phagocytosis was studied using RPE cultured on microporous filters, permitting control of which RPE surfaces are in contact with serum. Serum was found to have no influence on phagocytosis when present at the RPE basolateral surface, regardless of the serum concentration (2 or 20%). In contrast, phagocytosis was elevated three- to fivefold when 2% serum was present at the apical RPE surface, irrespective of the presence of serum at the basolateral surface. It is concluded that serum stimulates the phagocytosis of ROS only when the serum is present at the RPE apical surface.

Animals↗
PubMed1991

Requirement of insulin or IGF-1 for the maintenance of retinyl ester synthetase activity by cultured retinal pigment epithelial cells.

Previous work from these laboratories showed that the retention of retinyl ester synthetase activity by cultured human retinal pigment epithelium is up to tenfold greater with PM medium (Medium 199 plus insulin, other added defined components, 1% serum and 1% retina extract) than with conventional culture media. The present work shows that insulin is the component of PM medium required for maintenance of ester synthetase activity and that insulin-like growth factor type 1 (IGF-1) also is effective at maintaining ester synthesis. In addition, insulin can maintain ester synthetase activity in cultured rat RPE. Preliminary dose-response measurements provide additional support for these findings and strongly suggest that both insulin and IGF-1 are maximally effective at physiological concentrations (1-10 ng ml-1).

Acyltransferases↗
PubMed1991

Glycosaminoglycan degradation by cultured retinal pigment epithelium from patients with retinitis pigmentosa.

Patients with certain systemic deficiencies in the degradation of glycosaminoglycans (GAGs) often suffer from a retinal degeneration similar to that seen in retinitis pigmentosa. This applies to mucopolysaccharidosis (MPS) types I, II, and III, but not to type VI. The retinal pigment epithelium (RPE) is thought to contribute significantly to the synthesis and degradation of proteoglycans in the interphotoreceptor matrix. This raises the possibility that a defect in the synthesis or degradation of GAGs by the RPE may be related to some forms of retinal degeneration. In the present work, RPE from normal and RP donors was investigated for the capacity to correct deficiencies in GAG degradation by cultured skin fibroblasts from patients with different forms of MPS. A cross-correction technique was used in which abnormal increases in the incorporation of 35S-sulfate into GAGs by MPS fibroblasts was measured in the absence or presence of RPE cultures. RPE from normal donors corrected the defects in GAG degradation of fibroblasts from patients with MPS I, II, and III, but not MPS VI. The RPE from four donors with retinitis pigmentosa (one autosomal dominant, one sex-linked, and two isolated cases) and one donor with an unclassified isolated retinal degeneration demonstrated the same capacities to correct the MPS deficiencies as did normal RPE. Therefore, although retinitis pigmentosa is a heterogeneous disorder with several possible etiologies, no evidence was found in these five patients for a defect in GAG degradation that resembles the deficiencies of MPS patients.

Adult↗
PubMed1989

Use of B-mode, linear array ultrasonography for evaluating the technique of bovine artificial insemination.

B-Mode, linear array ultrasonography was used to evaluate the site of semen deposition in live cows. The insemination sheath was modified to hold a brass bead that was deposited at the simulated site of semen deposition. The position of the bead was identified by ultrasonography and the bead was recovered by pulling a nylon line that was attached to the bead. An ultrasound technician identified placement of the bead in the site designated for semen deposition by a skilled inseminator in 24 of 25 cases. This procedure improves methods for inseminator training by providing a method of evaluating insemination technique using live animals rather than excised reproductive tracts. The ultrasound equipment used for inseminator evaluation is affordable, portable, and does not pose a human health risk.

Animals↗
PubMed1988

Identification of proteins in retinas and IPM from eyes with retinitis pigmentosa.

Opsin, the alpha-subunit of transducin, S-antigen, interphotoreceptor retinoid-binding protein (IRBP) and cathepsin D were assessed in autopsy eyes from patients with retinitis pigmentosa (RP) and normal autopsy eyes. Immunochemical methods were used to determine the presence of these proteins on Western blots of retinal homogenates from five RP donors and on blots of interphotoreceptor matrix (IPM) preparations from six other RP eyes. The amounts of immunoreactive opsin, S-antigen, alpha-transducin, and IRBP appeared below normal in retinas from RP eyes. All six IPM samples from patients with advanced RP had reduced amounts of S-antigen and no detectable IRBP or transducin. Cathepsin D (an RPE protein) was present in IPM or RP eyes in amounts comparable to that in IPMs from normal eyes. Small amounts of cathepsin D were also detected in retinas from both normal and RP eyes. These studies show that proteins specific to the photoreceptor-pigment epithelium complex in normal eyes can be detected in autopsy eyes from patients with RP and suggest that the observed reductions in photoreceptor-specific proteins occur as a consequence of photoreceptor loss.

Adult↗
PubMed1987

Cyclic nucleotide phosphodiesterases in cultured normal and RCS rat pigment epithelium: kinetics of cyclic AMP and cyclic GMP hydrolysis.

Kinetically distinct classes of cyclic AMP (cAMP) and cyclic GMP (cGMP) phosphodiesterase activities (PDEs) were detected in homogenates of cultured pigment epithelium (PE) from both normal and Royal College of Surgeons (RCS) rats. PDE activities with apparent low Michaelis constants (Low Km cAMP- and cGMP-PDEs) were associated with the supernatant, while PDE activities with apparent high Michaelis constants (high Km cAMP- and cGMP-PDEs) were slightly higher in the pellet than in the supernatant after ultracentrifugation (100,000 g). Activity of the low Km PDEs was significantly reduced while that of high Km PDEs was not affected by known inhibitors of PDE. In both normal and RCS rat PE low Km PDEs required calcium and magnesium ions for optimal activity while the high Km PDEs required neither. In homogenates of cultured RCS rat pigment epithelium (PE), the kinetic parameters for cAMP- and cGMP-PDEs were comparable to normal, with the exception of the Km value of the low Km cGMP-PDE. This Km value was two-fold higher in the RCS compared with the normal (indicative of a reduced affinity for cGMP). It remains to be determined if the reduced affinity for cGMP in the RCS PE is related to the genetic defect which is expressed as a deficiency in the phagocytosis of outer segments by these cells.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1987

Characterization of retinal pigment epithelial cells cultured on microporous filters.

Retinal pigment epithelium (RPE) cultured on microporous filter supports was compared to RPE cultured on plastic and evaluated for features characteristic of RPE in vivo. RPE cells grown on filters were cuboidal, formed junctional complex structures between cells, and had elaborate microvilli and basal infoldings similar to RPE in vivo, while RPE grown on plastic also formed intercellular junctions but appeared squamous and had few microvilli and basal infoldings. RPE grown on filters or plastic secreted an extracellular matrix at the basal surface and ingested isolated rat rod outer segments at the apical surface. RPE grown on filters coated with laminin or fibronectin became confluent more rapidly than RPE grown on uncoated filters, while RPE grown at the same density on filters coated with collagen type I did not become confluent. The laminin and fibronectin coatings did not alter the RPE cell morphology; however, cells seeded on collagen-coated filters grew in large disorganized clusters. RPE grown on laminin-coated filters formed functional tight junctions as evidenced by the capacity of RPE monolayers to prevent the bulk flow of medium and the passage of trypan blue across the filter. Radiolabeled sucrose and inulin were used to measure the paracellular flux through the tight junctions between cells. The passage of these tracers was linear over time, with the lower molecular weight tracer, sucrose, passing through the monolayer more readily than inulin. Values for the flux of radiolabeled bovine serum albumin across RPE monolayers fell between values for sucrose and inulin. The results from these studies show that RPE monolayers cultured on laminin-coated filters maintain a morphology similar to that of RPE in vivo, are capable of ingesting rod outer segments, and form a selectively permeable barrier to various tracers. This culture system should be useful for studies of transepithelial transport, secretion, endocytosis and exocytosis that require independent control of the extracellular environment at the apical and basolateral cell surfaces.

Animals↗
PubMed1987

A 31,000-dalton protein released by cultured human retinal pigment epithelium.

Confluent primary cultures of human retinal pigment epithelium (RPE) were incubated for 3-14 hr with 35S-methionine, 3H-leucine, or 2-3H-mannose, and the released proteins were analyzed by SDS-polyacrylamide gel electrophoresis. A 31,000-dalton protein constituted 10-70% of the released radioactive proteins. The peak was degraded by pronase and its synthesis was inhibited by cycloheximide. The incorporation of 2-3H-mannose into this protein, and its inhibition by tunicamycin, showed that the protein is glycosylated. Monensin (10(-5) M) also inhibited the release of the 31,000-dalton glycoprotein. The released 31,000-dalton glycoprotein from human RPE comigrated on gels with a protein present in extracts of human interphotoreceptor matrix, raising the possibility that the released protein corresponds to a component of the matrix.

Adolescent↗
PubMed1986

Increased phagocytosis of outer segments in the presence of serum by cultured normal, but not dystrophic, rat retinal pigment epithelium.

Cultured normal rat retinal pigment epithelium (PE) ingested six times more rod outer segments in the presence of 20% fetal bovine serum than in serum-free medium. PE cultured from Royal College of Surgeons (RCS) rats with hereditary retinal dystrophy, known to have a defect in vivo in the phagocytosis of shed outer segment tips, ingested amounts of outer segments comparable to normal PE in serum-free medium but did not show an increase in the presence of serum. In both strains of rat PE phagocytosis of latex spheres was similar in the absence of serum and was six-fold higher in the presence of serum, showing that the RCS phagocytic deficiency for outer segments in vitro is not due to a general defect in the phagocytic capacity of the cell. Increased phagocytosis of outer segments by normal PE was observed in the presence of the high molecular weight fraction of ultrafiltered serum but was not seen with serum that was heated at 93 degrees C or precipitated with 5% trichloroacetic acid. Bovine serum albumin had no effect on phagocytosis. These results are consistent with the idea that the phagocytosis of outer segments by cultured normal rat PE, but not by cultured RCS rat PE, is increased in the presence of a specific protein or other macromolecular component of fetal bovine serum.

Animals↗