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Biomedical subjects

R H Clothier

Publications and source records attributed to R H Clothier.

At least 55 records · Page 3Linked to original sources
PubMed1984

In vitro thymus suppression of hemagglutinin production in Xenopus laevis: location, drug and temperature sensitivity.

Suppression of splenic hemagglutinin (HA) production by allothymuses in vitro was further studied in Xenopus laevis, the South African clawed toad. Since thymic capacity to suppress splenic HA secretion into the culture medium is retained in animals previously exposed to N-methyl-N-nitrosourea (NMU), which destroys the thymus cortex in this species, suppressor function must be located in the thymus medulla. Reciprocal thymus-spleen combinations showed that normal thymus can suppress immunised spleen fragments from NMU-treated animals. Since Xenopus exposed to NMU are also devoid of helper function, thymus suppression acts directly on the antibody forming system. Cyclophosphamide removed thymic suppression and enhanced spleen fragment antibody production, while Cyclosporin A enhanced thymic suppression and blocked HA production. Therefore, antigenic stimulation of thymic suppression and antibody production are inversely related in this species. Long-term storage of Xenopus in the cold increased lymphoid cellularity of the thymus medulla, but thymuses from cold-stored animals could not suppress normal spleen fragments and their spleens were not suppressed by normal thymuses. Thus, ectotherms may retain immunological capacity when subjected to prolonged cold by a loss of thymic suppression.

Animals↗
PubMed1984

TNP-Ficoll response in Xenopus laevis: substitution and reconstitution in thymectomized animals.

The capacity to respond to haptenated Ficoll, though thymus-independent in mammals, is lost in Xenopus laevis following thymectomy at any stage of development. This capacity can be restored to thymectomized Xenopus by whole allogeneic thymus implants, by thymus implants from animals treated with N-methyl-N-nitrosourea (which have an active thymus medulla but no cortex, and which lack certain thymus-dependent immunological functions), and Concanavalin A. These results are discussed in terms of the cell populations and/or factors which may be involved.

Animals↗
PubMed1982

Amphibian organ culture in experimental toxicology: the effects of paracetamol and phenacetin on cultured tissues from urodele and anuran amphibians.

Organ cultures of various tissues from urodele amphibians deacetylate paracetamol to p-aminophenol, which polymerises to form a brown precipitate. Paracetamol addition results in a loss of glycogen and lactate dehydrogenase (LDH) from urodele liver cultures and an increase in glucose release, and in LDH loss from kidney cultures. Organ cultures from anuran amphibians are unable to metabolise paracetamol and are not affected by its presence in the culture medium. The addition of unpolymerised p-aminophenol resulted in a loss of LDH from urodele and anuran organ cultures, whilst the addition of polymerised p-aminophenol had no such effects. This suggests that the toxic effects which follow the addition of paracetamol to urodele organ cultures are caused by unpolymerised p-aminophenol, a known toxicant in mammals. Cultures from both urodele and anuran amphibians are able to deacetylate phenacetin to p-phenetidine, but p-phenetidine was found to be much less toxic to amphibian tissues than p-aminophenol, causing LDH loss from kidney cultures only at very high dose levels.

Acetaminophen↗
PubMed1981

Location and release of TRH and 5-HT from amphibian skin.

The occurrence and release of thyrotrophin-releasing hormone (TRH) and 5-hydroxytryptamine (5-HT) from amphibian skin have been described by previous investigators. In the present study, the precise location and site of release of TRH and 5-HT from the skin of Rana pipiens and Xenopus laevis have been examined using a combination of procedures including immunohistochemistry, HPLC, and radioimmunoassay. The results indicate that TRH is located specifically within the dermal glands of these species, and that both TRH and 5-HT are discharged from these glands following adrenergic stimulation. The origin and functional significance of these substances in amphibian skin granular glands are discussed.

Animals↗
PubMed1981

A comparative study of the deacetylation of paracetamol by urodele and anuran amphibian organ cultures.

1. p-Aminophenol is the major metabolite produced by urodele amphibian tissues in vitro. The deacetylation enzyme system involved is located in the liver microsomal fraction of Amphiuma means. 2. Paracetamol was deacetylated to p-aminophenol by organ cultures of liver, kidney, pancreas and stomach epithelium from adult A. means, by liver, stomach epithelium, bladder and lung cultures from neotenic larval Ambystoma tigrinum, and by adult Triturus cristatus carnifex in vivo. 3. Liver cultures from all seven urodele amphibian species metabolized paracetamol and produced p-aminophenol, but no evidence was found of paracetamol metabolism by liver cultures from any of five anuran amphibian species. 4. The significance of p-aminophenol production from paracetamol and of this difference within the Amphibia are discussed.

Acetaminophen↗
PubMed1979

Effects of pH, Ca2+, temperature, and protease pretreatment on interkingdom fusion.

The incubation of carrot protoplasts and cultured Xenopus cells in a protease solution has been shown to enhance their subsequent interkingdom fusion by a high pH/high Ca2+ method. The effects of Ca2+ concentration, pH, and temperature on the frequency of heterokaryon formation have also been studied. Potentially viable heterokaryons have been repeatedly produced at high frequencies (consistently greater than 10%), far exceeding those so far achieved in PEG-mediated fusion. Cell aggregates are readily dispersed after this method of fusion, permitting the accurate estimation of fusion frequencies.

Animals↗
PubMed1978

The effects of alpha and beta adrenergic agents on spleen cell antigen binding in four amphibian species.

Adults of two urodele amphibian species (Triturus cristatus carnifex and Cynops hongkongensis) and two anuran species (Rana temporaria and Xenopus laevis laevis) were immunized with a 25% suspension of sheep or horse erythrocytes. After eight or 14 days, splenic lymphocytes were removed, and their specific red cell-binding capacities tested by immunocytoadherence. Antigen-binding cells were classified as high-dose nonsecretory (S-) or secretory (S+), according to whether they bound a single layer or several layers or erythrocytes. The stimulation of both alpha and beta adrenoreceptors reduced the numbers of S+ rosettes formed by Triturus and Cynops lymphocytes, whereas a beta agonist increased and an alpha agonist decreased S+ rosette formation by Rana and Xenopus splenic lymphocytes. These effects were blocked by alpha and beta adrenoreceptor antagonists. Low-dose immunization of Xenopus with a 0.0025% suspension of sheep erythrocytes gave a minimal number of S+ rosettes two and eight days after immunization, and beta adrenoreceptor stimulation had no effect on antigen binding. These results are discussed in terms of the distribution of alpha and beta adrenoreceptors in amphibians and possible relationships between S+ and high-dose S- antigen-binding cells, and support the view that functional lymphocyte heterogeneity exists in these lower vertebrates.

Amphibians↗
PubMed1978

The structure and ultrastructure of the renal tubule of the urodele amphibian, Amphiuma means.

The renal corpuscle and segments of the renal tubule of the urodele amphibian Amphiuma means have been described and studied by light and electron microscopy as a background for investigations on the effects of hormones, drugs, toxins and carcinogens on cell structure and function in long-term organ cultures of kidney explants. Notable features of the A. means kidney include the number and variety of cytoplasmic inclusions in the cells of the proximal segment, the comparatively thick glomerular filter, and the presence of possible renin granules in the endothelial cells lining the afferent arteriole near its point of entry to the glomerular capsule.

Animals↗
PubMedDate not supplied

Apoptosis in thymus of adult Xenopus laevis.

Thymocyte apoptosis in adult Xenopus laevis is demonstrated on agarose gels and is quantified by propidium iodide incorporation using flow cytometry. Basal apoptotic levels are increased after in vitro exposure to a glucocorticoid, dexamethasone (DEX), and to the lectin, phytohemagglutinin (PHA). To determine the role that newly introduced antigenic determinants may play in this regard, a repertoire of altered-self antigens was created by exposing thymuses in vitro to trinitrobenzene sulfonic acid (TNBS) thereby derivatizing self-cells and proteins via 2,4,6-trinitrophenyl-acetic acid conjugation. An increase in apoptosis in TNBS-treated thymuses is observed. Thus, the thymocytes of adult Xenopus laevis are susceptible to apoptosis when induced by a glucocorticoid, a lectin, and by altered self, antigen activation.

Animals↗
PubMedDate not supplied

The development of peripheral TNP-tolerance and suppressor function in Xenopus laevis, the South African clawed toad.

In adult Xenopus laevis, inducer- and effector-suppressor functions are located in the spleen. These peripheral suppressor functions must be established at this location near the end of metamorphosis, since both functions are in the thymus in premetamorphic and in developmentally-blocked metamorphosing larvae. This study examined whether TNP-conjugated self-antigens resulting from exposure to trinitrobenzene sulfonic acid (TNBS), will stimulate TNP-tolerance in premetamorphic, metamorphic, and in developmentally-blocked metamorphosing larvae. Premetamorphic and developmentally-blocked larvae produce little TNP-tolerance or peripheral suppressor function. However, when TNBS exposure includes the late stages of the metamorphic period, both TNP-tolerance and splenic anti-hapten suppressor function are demonstrable. Removal of suppressor function with cyclophosphamide prevents expression of tolerance, thus, they are functionally related. Suppressor function and tolerance both differentiate during the late metamorphic stages when new adult antigens are being expressed and incorporated into a library of self.

Animals↗
PubMedDate not supplied

An evaluation of three in vitro cytotoxicity assays.

A number of methods for determining the general toxic effects of test chemicals on cells in culture are now at the validation stage. Three such methods based on measurement of total cell protein or neutral red uptake and on the detection of morphological effects have been compared. The cell line used was 3T3-L1 (a continuous fibroblast cell line derived from mouse embryos). The results obtained in a blind trial with 30 coded chemicals indicated a close correlation between the relative cytotoxicities of chemicals tested by all three methods.

Cell Survival↗