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Biomedical subjects

T Ma

Publications and source records attributed to T Ma.

At least 163 records · Page 9Linked to original sources
PubMed1990

Regulation of polyethylene glycol 400 intestinal permeability by endogenous and exogenous prostanoids. Influence of non-steroidal anti-inflammatory drugs.

Polyethylene glycol 400 (PEG 400) is a clinically useful intestinal permeability probe whose rate of intestinal permeation is influenced in part by solvent drag. As mucosal prostanoids are increased in inflammatory bowel disease and affect water transport we examined the possible relationship between prostaglandin E2 (PGE2) and the inhibitors of endogenous prostaglandins--the non-steroidal anti-inflammatory drugs (NSAIDS)--on PEG 400 absorption in vivo using segmental perfusion of rat small intestine. We found that the addition of exogenous PGE2 in concentrations of 0.5, 1.0, and 1.5 micrograms/ml significantly (p less than 0.01) decreased PEG 400 and water absorption. Addition of 5 mmol/l of the cyclooxygenase inhibitors acetylsalicylic acid (ASA) or indomethacin in concentrations 2.5 or 5.0 mmol/l to the perfusate significantly (p less than 0.01) increased PEG 400 and water absorption. The simultaneous addition of 1.0 micrograms/ml of exogenous PGE2 to the perfusate with 5 mmol/l of ASA or with 2.5 mmol/l of indomethacin reversed the increase of PEG 400 and water transport (p less than 0.01). There were no differences in PEG 400 and water absorption when PGE2 was given alone or in combination with ASA or indomethacin. This study suggests that endogenous or exogenous prostanoids play an important role in the regulation of PEG 400 permeation. PGE2 and NSAIDS modify PEG 400 permeation in parallel with changes in water transport indicating that their effect on permeability is through changes in solvent drag. These findings provide a mechanism which might explain the increase in PEG 400 intestinal permeability in Crohn's disease patients and the increase in intestinal permeability found in patients receiving NSAIDS.

16,16-Dimethylprostaglandin E2↗
PubMed1989

Polyethylene glycol 900 permeability of rat intestinal and colonic segments in vivo and brush border membrane vesicles in vitro.

Increased intestinal absorption of medium-sized aqueous probes has been found in patients with a variety of disorders. We studied the physiologic control mechanisms, intestinal regions, and effects of lumenal factors on the intestinal absorption of polyethylene glycol (PEG) 900 in the rat in vivo and in rabbit brush border membrane vesicles (BBMVs). The kinetics of PEG 900 intestinal absorption were compatible with simple passive diffusion. Because transport across BBMVs was minimal, we concluded that transport of PEG 900 is mostly through the paracellular tight junctions. Absorption was highest in the midcolon (104.3 +/- 9.5 mumol/100 mg protein per hour vs 9.1 +/- 1.2 mumol/100 mg protein per hour in the jejunum). Absorption was decreased by higher lumenal osmolarity (greater than 400 mOsm/L) after the additions of 2.5 to 5.0 mmol/L chenodeoxycholate or 2.5 mmol/L lysolecithin, or at higher lumenal flow rates (greater than 1 ml/minute), higher lumenal pressure (7.5 cm H2O),or higher lumenal pH (8.0). Lipid solubility of PEG 900 was less than 0.00079%. Under all experimental conditions, PEG net absorption followed changes in water transport. When water transport changed from absorption to secretion, PEG absorption decreased. When water absorption increased, PEG 900 absorption increased in parallel. We conclude that PEG 900 is absorbed by passive diffusion that is modulated by solvent drag and is maximal in the midcolon. Transport directly across cell membranes is mimimal, but overall PEG 900 permeability is closely linked to water absorption by solvent drag and takes place primarily through the paracellular junctions. We propose that these features and mechanisms of PEG 900 transport make PEG 900 a suitable probe molecule for studying intestinal permeability changes.

Animals↗
PubMed1988

The effects of high iodine on the brain development of mice.

C57 mice were divided into two groups: (A): experiment group (H group). Each female mouse was injected with 20 microliter iodized oil; (B): control group (N group). Both groups were mated 8 days after iodized oil injection. Urine iodine contents/24 h of H group was 20 times higher than that in N group 7 days after injection and 18 times higher two months later. Serum T4 values were determined. Brain protein, DNA, body weight, motility and learning ability were measured in the progeny. The results indicate that there was no statistically significant difference between the groups in any of the parameters mentioned above. This strongly suggests that a high iodine dose, given as iodized oil, does not have obvious damaging effects on brain development, at least in mice.

Animals↗
PubMed1988

Chairside color verification for facial prostheses.

The coloring technique may be used for facial prosthetic materials that can be processed in gypsum molds. With different surface textures and varying thicknesses built into the technique, it is a reliable method for color verification of facial prosthesis before final processing.

Color↗
PubMed1988

Kinetics of gamma interferon binding and induction of major histocompatibility complex class II mRNA in Leishmania-infected macrophages.

Cells of the monocyte-macrophage series must carry out discrete accessory-cell functions during the process of antigen-specific T-cell activation. One of these functions is the cell-surface expression of major histocompatibility complex (MHC) class II gene products, which are involved in the presentation of foreign antigen to T cells. Previously, we reported that murine peritoneal macrophages infected with the obligate intracellular protozoan Leishmania donovani had suppressed responses to gamma interferon (IFN-gamma) for the induction of MHC class II antigen expression. To determine the molecular basis for this suppression, we examined in the present series of experiments the interaction of this organism with cells of the murine macrophage tumor cell line P388D1. When infected with Leishmania, these cells were also markedly unresponsive to IFN-gamma for the induction of MHC class II antigen expression. This finding was not the result of a defect at the level of the IFN-gamma receptor. Thus, when 125I-labeled IFN-gamma was used, infected macrophages were found to express normal numbers of high-affinity IFN-gamma receptors, and ligand-receptor binding resulted in rapid internalization of labeled IFN-gamma. Despite normal ligand-receptor interactions, the induction in infected cells of mRNA encoding MHC (H-2) class II I-A alpha and beta chains in response to IFN-gamma was markedly suppressed. However, infected cells had normal levels of mRNA encoding the cytoskeletal protein actin. These findings indicate that Leishmania interferes with IFN-gamma induction of macrophage MHC class II antigen expression by down-regulating lymphokine induction of MHC class II mRNA. Suppression of class II expression by this intracellular parasite may prevent subsequent T-cell recognition of infected macrophages and thus favor parasite survival.

Animals↗
PubMed1987

The color accuracy of the Kubelka-Munk theory for various colorants in maxillofacial prosthetic material.

The reflectance model developed by Kubelka and Munk was evaluated for agreement in color prediction of thick pigmented samples and for linearity of optical absorption and scattering coefficients with concentration of colorant in maxillofacial elastomer. The colorants tested were generic opacifiers, dry mineral earth pigments, and fibrous colorants. Significant linear relationships were commonly found between the optical coefficients and the concentration of the colorants. These relationships indicated occasional optical interaction between the colorants and the elastomer. Color differences between theoretical and observed colors of the thick samples averaged 2.96, 3.47, and 1.60 for the opacifiers, mineral earth pigments, and fibrous colorants, respectively, when measured using the CIELAB uniform-color space. The agreement between theoretical and observed colors was significantly closer for the fibrous colorants than for the dry mineral earth pigments of the same labeled color.

Color↗
PubMed1983

Nonenzymatic separation of myocardial cell nuclei from whole heart tissue.

A simple and rapid nonenzymatic method has been developed to isolate myocardial cell nuclei from whole heart tissue. This method consists of a controlled disruption of cells followed by isopycnic gradient centrifugation. We have reviewed and compared our method to others more lengthy and laborious. By using a number of criteria, such as morphometric measurements, chemical composition, functional studies, specific nuclear protein markers, and mathematical analysis, we show that the nonenzymatic digestion method provides a most useful technique for the study of the biochemistry of the myocardial cell nucleus.

Aging↗
PubMed1980

A comparison of cognitive impairment due to benzodiazepines and to narcotics.

In an attempt to determine the source of cognitive impairment in 106 consecutively admitted patients at the Johns Hopkins Chronic Pain Treatment Center, EEG, the Wechsler Adult Intelligence Scale, Memory Quotient, and Bender Gestalt tests were administered. Patients receiving benzodiazepines alone demonstrated alterations in cognitive functioning and EEG evidence of a sedative effect. Patients receiving narcotics alone and a group of patients not receiving medication did not show signs of cognitive impairment. The effects of benzodiazepines on sleep and perception of chronic pain, in combination with the cortical changes that they produce, imply that these drugs should not be used in most patients with chronic pain.

Adult↗
PubMedDate not supplied

Effects of filtration seeding on cell density, spatial distribution, and proliferation in nonwoven fibrous matrices.

The cell seeding density and spatial distribution in a 3-D scaffold are critical to the morphogenetic development of an engineered tissue. A dynamic depth-filtration seeding method was developed to improve the initial cell seeding density and spatial distribution in 3-D nonwoven fibrous matrices commonly used as tissue scaffolds. In this work, trophoblast-like ED27 cells were seeded in poly(ethylene terephthalate) (PET) matrices with various porosities (0.85-0.93). The effects of the initial concentration of cells in the suspension used to seed the PET matrix and the pore size of the matrix on the resulting seeding density and subsequent cell proliferation and tissue development were studied. Compared to the conventional static seeding method, the dynamic depth-filtration seeding method gave a significantly higher initial seeding density (2-4 x 10(7) vs 4 x 10(6) cells/cm3), more uniform cell distribution, and a higher final cell density in the tissue scaffold. The more uniform initial cell spatial distribution from the filtration seeding method also led to more cells in S phase and a prolonged proliferation period. However, both uniform spatial cell distribution and the pore size of the matrices are important to cell proliferation and morphological development in the seeded tissue scaffold. Large-pore matrices led to the formation of cell aggregates and thus might reduce cell proliferation. The dynamic depth-filtration seeding method is better in providing a higher initial seeding density and more uniform cell distribution and is easier to apply to large tissue scaffolds. A depth-filtration model was also developed and can be used to simulate the seeding process and to predict the maximum initial seeding densities in matrices with different porosities.

Biocompatible Materials↗
PubMedDate not supplied

Tissue engineering human placenta trophoblast cells in 3-D fibrous matrix: spatial effects on cell proliferation and function.

Nonwoven polyethylene teraphathalate (PET) fabrics with different porosities and knitted fabric were used as support matrixes to grow human trophoblast cells to study the spatial effects of fibrous matrix on cell adhesion, spatial organization, proliferation, and metabolic functions. In general, cells grown on 2-D surface and knitted fabric had faster metabolic rates and also showed higher proliferation activities as detected by cyclin B assay. For nonwoven PET fibers, matrix porosity had profound effects on cell morphology, spatial organization, and proliferation. Cells grown in a low-porosity fibrous matrix formed small aggregates ( approximately 100 cells per aggregate), whereas cells grown in high-porosity matrix formed big aggregates ( approximately 1000 cells per aggregate). This was attributed to the difference in pore volume or averaged fiber distance, which dictated a cell's ability to cross over and form a bridge between adjacent fibers. The high-porosity matrix had a relatively poor surface accessibility for cells to attach and spread, which are essential for cell proliferation. Dual staining with PI and BrdU showed that 60% of cells in the small aggregates found in the low-porosity matrix were proliferating, while only 18% of cells in the large aggregates found in the high-porosity matrix were proliferating. These results suggest that spatial characteristics of fibrous matrix are important to cell proliferation and function and should be considered in tissue-engineering human cells.

Biocompatible Materials↗