Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “microenvironment”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,207 records · Page 67Linked to original sources
PubMed1989

Blood-nerve transfer of albumin and its implications for the endoneurial microenvironment.

Blood-nerve transfer of plasma albumin was studied by measuring the permeability coefficient-surface area (PS) product of the blood-nerve barrier (BNB) to 125I-albumin in rat sciatic nerve using the i.v. bolus injection method. The calculated PS was 6.3 +/- 0.5 (S.E.M.) x 10(-7) ml.g-1.s-1. This value is smaller by more than an order of magnitude of that measured for sucrose and confirms the relative impermeance of the BNB to blood-borne solutes. From a review of the available evidence, it is concluded that normal blood-nerve exchange occurs predominantly across the endoneurial microvasculature, and the PS of the BNB reflects the permeability of capillaries to a greater extent than that of the perineurium. The only capillaries found to be less permeable than these are the cerebral capillaries. Proximo-distal differences (sciatic vs tibial) of the PS could not be detected. Blood-nerve albumin transfer was calculated at 1.2 mg.g-1.day-1, and the daily turnover of endoneurial albumin to be about 30%. It is postulated that small increases in PS of BNB to albumin lead to an elevation of endoneurial albumin concentration and, through the operation of Starling forces, subsequently produce endoneurial oedema. A major question posed by the results of this study is the identity of pathways for clearance of albumin and other macromolecules from the endoneurium.

Animals↗
PubMed1990

Endoneurial microenvironment and acute nerve crush injury in the rat sciatic nerve.

In severe peripheral nerve ischemia in the rat, serial nerve blood flow (NBF) measurements have identified evidence of 'no reflow', a mechanism of continued fiber damage during reperfusion. It has been postulated that 'no reflow' also occurs in nerve compression due to direct mechanical or ischemic (if compression is prolonged) injury of microvessels, resulting in continuing nerve fiber damage. To address this question, we measured endoneurial blood flow (NBF), oxygen tension and pH at the site of an acute nerve crush injury. In further sets of experiments, NBF and endoneurial oxygen tension were examined before and after prolonged epochs of crush. NBF and MR (microvascular resistance) were not appreciably different than values obtained in control animals without intervening brief nerve crush. NBF was slightly higher and MR slightly lower 2 h after injury, but the difference was not statistically significant. No evidence of significant endoneurial hypoxia or acidosis was observed. Similarly, after more prolonged crush there was no significant oligemia or hypoxia. The studies provide no evidence that 'no reflow' occurs in crush injury even if the injury is maintained for a period of time known to induce 'no reflow' with severe ischemia. We suggest that nerve damage in crush, and possibly compression, more likely arises from direct mechanical injury of fibers.

Animals↗
PubMed1983

Phytohemagglutinin-induced acquisition of T-cell surface markers by rat bone marrow precursor cells in the absence of the thymic microenvironment.

Two monoclonal antibodies specific for different rat T-cell subpopulations, the anti-helper-T-cell antibody, W3/25, and the OX8 suppressor cell antibody were used to investigate lectin-stimulated T-lymphocyte differentiation of F-344 rat bone marrow cells in culture. Cytofluorometric analysis of freshly isolated lymphocytes from thymus and spleen revealed that these tissues contained both W3/25- and OX8-positive populations but differed with respect to the number of cells and receptor density distribution. By contrast, bone marrow-derived lymphocytes exhibited negligible W3/25- or OX8-associated fluorescence. However, several days after stimulation of bone marrow lymphocytes with phytohemagglutinin (PHA), cells appeared bearing these markers. Two-parameter histogram analysis of light scatter measurements with cell surface immunofluorescence indicated that this phenomenon represented the appearance of a new population of cells, presumably mature T cells, bearing an increased density of marker. These findings suggest an induction of differentiation of bone marrow T precursor cells by nonthymic factors (PHA) since lymphocytes lacking mature T-cell marker expression developed this characteristic after several days in culture.

Animals↗
PubMed1987

A chemotactic factor for rat thymocytes may regulate T-lymphocyte migration toward the thymic microenvironment.

Using a modified Boyden chamber assay, extracts or culture supernatants of rat thymic stromal cells, or thymocytes were examined by chemotactic activity to rat leukocytes. Rat thymocytes responded chemotactically to the aqueous extract as well as to culture supernatants of thymic stromal cells. However, neither the extract and culture medium from concanavalin A-stimulated thymocytes nor any component of rat serum has shown such an activity. The thymic extract was fractionated into three molecular species with chemotactic activity for thymocytes. The thymocyte chemotactic factor(s) (TCFs) in the extract was distinct from known lymphocytic chemotactic factors, such as interleukin-1 (IL-1), IL-2, C5a, and the culture supernatant of stimulated thymocytes. In vitro, TCFs could attract, in addition to thymocytes, bone marrow cells, fetal liver cells, and nylon-wool nonadherent lymphocytes from peripheral blood and spleen. Lymph node cells, neutrophils, macrophages, and B cells from peripheral blood could not respond to TCFs. Thymocytes also responded to the extract of splenic stromal cells. Unlike the thymic extract, however, the splenic extract was chemotactically active for lymphocytes from lymph nodes but not for bone marrow cells. These results indicate that thymic stromal cells secrete a chemotactic factor(s) for a relatively immature type of T-lineage cells, which may by a thymus-homing progenitor T cell, while spleen may contain an attractant for a relatively mature type of T-lineage cells.

Animals↗
PubMed1991

Extracellular matrix components of the mouse thymic microenvironment. II. In vitro modulation of basement membrane proteins by interferon-gamma: relationship with thymic epithelial cell proliferation.

We studied the effects of recombinant interferon-gamma (IFN-gamma) on some aspects of the physiology of two murine thymic epithelial cell (TEC) lines. Besides the expected induction of MHC class II antigens, this lymphokine was able to modulate the extracellular matrix (ECM) expression by growing TEC, as well as modulate their adhesion and proliferation patterns. As regards the influence of rIFN-gamma on ECM expression, we observed that when applied in very low doses, it promoted an increase in the amounts of basement membrane proteins, mainly fibronectin. In contrast, relatively high doses of this lymphokine (10(1) to 10(2) IU/ml) induced the opposite effect. Interestingly, both the stimulatory and the blocking effects of IFN-gamma on ECM expression were paralleled by equivalent modulation of cell proliferation, in both mouse and rat TEC lines. It should be pointed out that all these effects could be significantly abrogated by an anti-IFN-gamma monoclonal antibody. Searching for a putative mechanism that could be involved in the modulation of TEC proliferation by IFN-gamma, we observed a clear-cut positive correlation between cell adhesion and proliferation of TEC growing onto ECM-containing substrata produced following IFN-gamma treatment. The bulk of the data presented herein suggests that IFN-gamma may play a relevant role in TEC physiology and ontogeny, not only by inducing MHC class II antigen expression but also by regulating TEC growth via the control of extracellular matrix production by these cells.

Animals↗
PubMedDate not supplied

A model of regional ventilation-perfusion inhomogeneity in the avian lung. Implications for gas exchange and intrapulmonary chemoreceptor microenvironment.

We recorded discharge frequencies of 32 intrapulmonary chemoreceptors (IPC) during caudocranial and craniocaudal ventilation in the perfused duck lung. Blood gases, ventilatory gas flow, inspired PCO2 and PO2, and expired PCO2 measured simultaneously were used to predict regional CO2 and O2 gradients within the lung. Gas exchange was modelled in 7 log normal ventilation-perfusion compartments using mass balance differentials with an adjustable step size. CO2 and O2 interactions during exchange were modelled using the Bohr effect, P50, blood acid-base status, and the CO2 dissociation relationship. Close agreement (+/- 1.0 Torr) between simulated arterial and expired PCO2 and observed values was achieved after forcing simulated PaO2 to converge on observed PaO2 by an iterative adjustment of the perfusive shunt or the log standard deviation of the ventilation-perfusion distribution. Using the IPC static CO2 sensitivity measured in the non-perfused lung and the CO2 gradients generated by the model, we have found evidence for a distributed multi-ending receptor system in the duck lung.

Animals↗
PubMed1986

Coordinate regulation of the expression of axonal proteins by the axonal microenvironment.

The axonal functions that act in the formation of the neuronal network have been shown to occur in close interdependence with the tissue that surrounds the growing axons. However, little is known about the molecular building blocks underlying axonal functions, although more than 400 axonal proteins have been identified. In view of the existence of such a large number of axonal proteins, we have initiated a project to determine the molecules involved in the implementation of particular axonal functions by a selective approach. On the assumption that plasticity in the expression of axonal functions in response to specific features of the local axonal environment may be based on changes in the expression of particular axonal proteins, the axonal proteins of dorsal root ganglion (DRG) neurons were screened for those whose expression responds to environmental influences. DRG neurons were grown in a compartmental cell system that offers separate access to neuronal somas and to their axons and the axons were locally exposed to different populations of cells from the peripheral or central nervous system. The axonal proteins were metabolically labeled and subjected to two-dimensional gel electrophoresis. Computerized quantitation of the individual axonal proteins revealed that the cocultured cells modulate the synthesis of a few axonal proteins of DRG neurons differentially. The data on the abundance of the newly expressed proteins under varying local environmental conditions were condensed as expression profiles. Comparison of expression profiles and cluster analysis of quantitative gel analysis data revealed that the environmentally modulated proteins subdivide into clusters with common distinct expression profiles under the influence of nonneuronal cells from the peripheral nervous system, nonneuronal cells of the central nervous system, and spinal cord cells, which are composed of neurons and nonneuronal cells. By means of this new, characteristic attribute assigned to environmentally modulated axonal proteins, working hypotheses were made as to their functional role.

Animals↗
PubMed1986

The pathophysiology of the ocular microenvironment. II. Copper-induced ocular inflammation and hypotony.

The ocular effects of intravitreally injected copper sulfate solutions were studied in New Zealand white rabbits. These injections resulted in uveitis characterized by prolonged ocular hypotony, increased protein concentrations and decreased ascorbic acid concentrations in both the vitreous and aqueous humors, and an apparent decrease in the transport function of the anterior uvea. The extent and the duration of these effects were dose-dependent. The lower doses used, 3 or 6 micrograms of Cu as CuSO4 per eye, produced reversible inflammation. The highest dose, 30 micrograms of Cu per eye, also produced some signs of ocular chalcosis: hemorrhage, vitreous liquefaction, prolonged hypotony and local iridial ischemia. Six hours after the intravitreal injection of 6 micrograms of Cu as CuSO4 per eye, the Cu concentration in the vitreous humor increased to approximately 100 times that in the vitreous of control eyes, and began to decline only 3 days later, with a half-time of approximately 8 days. The Cu concentration in the anterior chamber of these eyes never exceeded 1 ppm and returned close to control values within 3 days. Based on these findings, factors that affect ocular trace-metal distribution and kinetics are discussed, as are reasons for the apparent difficulty in diagnosing the presence of Cu-containing intraocular foreign bodies on the basis of the Cu concentration of the aqueous humor.

Animals↗
PubMed1983

The microenvironment of the spinal ganglion neuron in the rat during aging.

The environment and particularly the glial sheath of the spinal ganglion neurons was systematically studied by light and electron microscopy in the young and senescent rat. Experiments using radioactive tracers tested the consequences of the functional perturbations associated with structural impairments. The results suggested the possibility that the glial sheath and the neuron aged differently. Whereas the glial sheath maintained its functional capacity relatively intact, neuronal performance was markedly and more rapidly impeded. The morphology and volume of the extracellular space were unchanged. Therefore, impairment of the glioneuronal units in the spinal ganglion during aging cannot be assigned to environmental and vascular phenomena.

Aging↗
PubMed1995

Analysis of the acidic microenvironment in murine tumours by high-performance ion chromatography.

High-performance ion chromatography (HPIC) has been utilised to probe the biochemistry associated with changes in tumour pH following total vascular occlusion. Samples from the tumour extracellular compartment were obtained by insertion of a microdialysis probe and analysed by HPIC with conductivity detection. Separations were carried out by ion-exclusion chromatography using an IonPac ICE AS1 weak-acid column. The eluent (0.5 mM octanesulphonic acid) was chemically suppressed with 5 mM tetrabutylammonium hydroxide through a micromembrane suppressor. After complete vascular occlusion induced by a clamp, lactate levels increased in the extracellular compartment.

Animals↗
PubMed1991

Abnormalities associated with the bursal microenvironment in spontaneous dysgammaglobulinemia of UCD line 140 chickens.

UCD line 140 chickens have been previously reported to develop a syndrome of spontaneous 7s immunoglobulin deficiency and the presence of autoantibodies. Earlier studies demonstrated that these inbred birds have normal peripheral blood T and B cell numbers; they also respond normally to allogeneic stimulation. Although the 7s immunodeficiency does not manifest itself until several months of age, line 140 birds have a premature degeneration of bursa. Because of the recent development of monoclonal reagents specific for bursal elements, including surface epithelium, basement membrane associated epithelium, follicle associated epithelium, and lymphoid subpopulations, we have examined line 140 and control birds for the expression of bursal epithelial cell antigens. Line 140 birds, in contrast to control chickens, have a dramatic early alteration in the expression of an epithelial cell marker in the bursa, thymus, and intestine. Moreover, to further address this issue, we transplanted bursa from 10-day embryos onto the chorioallantoic membrane, a privileged site. Bursae from control birds became abnormal when transplanted onto line 140 CAM; they remained normal when transplanted among several control chicken lines. In contrast, line 140 bursa remained abnormal independent of the transplant procedure. Due to the marked bursal abnormality observed specific to the dysgammaglobulinemia chicken line, we propose that the microenvironmental features of line 140 bursa may predispose these birds to the development of humoral immunodeficiency and autoantibodies.

Animals↗
PubMed1986

Cellular aspects of radiation leukemogenesis in C57 BL/Ka mice: alterations to thymic microenvironment and lymphopoiesis.

After a leukemogenic split dose course of irradiation, thymic nurse cells (TNCs) disappear. We have correlated this with the loss of an epithelial cell surface antigen (recognized by monoclonal antibody ER-TR3 and tentatively identified as Ia). In addition, epithelial cells have lost their capacity to interact with fetal thymocytes in vitro. Marrow grafting early after irradiation, that prevents the development of lymphomas, restores thymic nurse cells and thymocyte population. Such reconstitution and lymphoma prevention were not observed when marrow grafting was performed later (1 month after irradiation) during the preleukemic period.

Animals↗