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Biomedical subjects

B Singh

Publications and source records attributed to B Singh.

At least 793 records · Page 44Linked to original sources
PubMed1983

Separation of different cell populations of rat liver by density gradient centrifugation in a vertical rotor with self-generated Percoll gradients.

A procedure is described which, with good resolution, separates viable rat liver parenchymal cells from other cell populations present in crude suspensions of liver cells. Fractionation is carried out by vertical rotor centrifugation in a self-generated Percoll gradient. Kupffer cells can be separated from other sinusoidal cells, resulting in a separate peak of peroxidase negative non-parenchymal cells, composed mainly of endothelial cells.

Animals↗
PubMed1983

Monoclonal antibodies against colonization factor antigen I pili from enterotoxigenic Escherichia coli.

Hybridomas secreting monoclonal antibodies directed against intact colonization factor antigen I pili have been produced by the fusion of spleen cells from immunized BALB/c mice with NS1/SP2 myeloma cells. The four monoclones with the highest antibody titer, as detected by enzyme-linked immunosorbant assay (ELISA), were chosen for antibody amplification by production of mouse ascitic fluid. These four were examined for antibody specificity by ELISA and immunoblot assays, using six different pilus types. Three of the four monoclonal isolates were specific for only colonization factor antigen I pili in both assays, whereas the remaining isolate showed a distinct cross-reactivity with K99 pili in the ELISA assay but not in immunoblot analysis. These results indicate that this monoclone may be recognizing a common structural element between the two adhesive pilus types.

Animals↗
PubMed1983

Post-hysterectomy adaptation: a review and report of two follow-up studies.

Hysterectomy, its indications and its consequences for later health, have been prominent topics in recent psychiatric, gynaecological and lay literature. This study describes the results of two recent surveys, one of 216 women less than 45 years old who had a hysterectomy for non-malignant conditions at a major Sydney hospital. These women were interviewed on the seventh to tenth postoperative day. One hundred and ninety-four were then followed up by questionnaire 13 months later. In a later study carried out at a hospital on the outskirts of Sydney, 100 out of 146 women responded to a follow-up questionnaire approximately one year after their operations. These studies and their relevance to recent similar studies are discussed in terms of post-hysterectomy adaptation and prognostic factors associated with poor psychiatric outcome.

Adaptation, Psychological↗
PubMed1983

Ambient air concentration of asbestos fibres, dust content and mortality: the case of Asbestos, Quebec.

Ambient air concentrations of asbestos fibres were measured during the period 20 June to 12 August, 1980 at three locations; Danville, Asbestos and Wottenville in the eastern townships of Quebec. Measurements were made with low-volume samplers and measurement periods ranged from 3 to 13 days. Fibre counts were made by means of electron microscopy. Our results indicate that overall fibre concentrations are related to atmospheric stability and to the direction of the prevailing wind with respect to the source of emission. Fibre concentrations are then related to total dust content of the ambient air for the town of Asbestos. Spatial variations of mortality are in turn related to the variations in the concentration of ambient air dust particles.

Air Movements↗
PubMed1983

Mutagenic responses of thirteen anticancer drugs on mutation induction at multiple genetic loci and on sister chromatid exchanges in Chinese hamster ovary cells.

The mutagenic responses of 13 antineoplastic drugs, namely, chlorambucil, busulfan, lomustine, dacarbazine, Adriamycin, daunomycin, bleomycin, VM-26, VP16-213, ellipticine, actinomycin D, mitomycin C, and cis-diamminedichloroplatinum(II) have been determined in two different assay systems in Chinese hamster ovary cells which measure mutation induction at multiple genetic loci and the frequencies of sister chromatid exchanges. The five genetic loci whose responses have been measured include those conferring resistance to 6-thioguanine (Thgr or TGr), ouabain, emetine, methylglyoxal bis(guanylhydrazone), and 5,6-dichlororibofuranosylbenzimidazole; of these, only the Thgr marker affects a function (hypoxanthine-guanine phosphoribosyltransferase, hgprt locus) which is not essential for cellular growth. All of these drugs showed a dose-dependent increase in mutation frequency at the hgprt locus, but their responses at other genetic loci differed greatly and showed marked specificity for different chemical classes of the drugs. The observed locus-specific differences in response to these drugs suggest that they may differ in terms of their accessibility or affinity to different chromosomal regions. All of these drugs also led to a significant increase in the frequency of sister chromatid exchanges, and a very good correlation was observed between the activity of these drugs in the sister chromatid exchange assay and the mutagenic response of the hgprt locus. Of the drugs which were examined, VM-26, VP16-213, chlorambucil, mitomycin C, and cis-diamminedichloroplatinum(II) showed a particularly strong response in both of these assay systems. In terms of the minimum concentration which gave a mutagenic response, the drugs differed from each other by a factor of about 100,000, with actinomycin D, VM-26, and daunomycin being mutagenic in the range of 3 x 10(-8) to 1 x 10(-7) M, whereas dacarbazine produced a weak mutagenic response only at about 2 x 10(-3) M.

Animals↗
PubMed1982

Primary and secondary structure in a precursor of 5 S rRNA.

In order to shed some light on the mechanism of action of RNAase E, we studied primary and secondary structure in 9 S (a precursor of 5 S rRNA), p5 and 5 S rRNAs. These molecules were digested with RNAases A and T1 in the presence of a high salt concentration; conditions under which single-stranded RNA is differentially digested. The double-stranded RNA fragments were isolated and analyzed. The analyses suggested that p5 and 5 S rRNA contain a stem of ten basepairs which consists of sequences from the 5' and 3' regions of the molecule, while 9 S contains a similar stem which is three basepairs longer and includes also a bulge of three unpaired bases. The stem in the 9 S RNA contains four sites where RNA processing cleavages occur. One of the cleavage sites which leads to the formation of p5 is in a junction between single-stranded and double-stranded RNA. The 9 S RNA molecule contains another large stem of at least 15 basepairs which is derived from the 3' end of the 9 S precursor molecular; it is apparently the transcription termination stem.

Base Sequence↗
PubMed1982

Mutagenic response to ultraviolet light and X-rays at five independent genetic loci in Chinese hamster ovary cells.

The mutagenic response to ultraviolet light and X-irradiation at a number of well characterized independent genetic loci, viz those conferring resistance to 6-thioguanine, ouabain, emetine, methylglyoxal (bis) guanylhydrazone (MGBG), and 5, 6-dichlororibofuranosyl benzimidazole (DRB), has been determined. Upon exposure of cells to UV light in the range of 70 to 180 ergs/mm2, the frequency of mutants at all of the above genetic loci increased in a linear dose-dependent manner. However, some genetic-locus-specific differences in response to UV light were observed in these studies. In contrast to UV light, exposure of cells to X-rays caused a linear dose-dependent increase in the frequency of mutants at only the thioguanine-resistant (Thgr) locus, which affects the purine salvage pathway enzyme hypoxanthine-guanine phosphoribosyltransferase, that is not essential for growth under these conditions. The other genetic loci that affect essential cellular functions (and hence should detect only specific base substitution types of mutations), however, showed no increase in the frequencies of mutants upon X-irradiation of cells. These results are in accordance with the nature of the genetic lesions which are caused by these agents and the properties of these genetic markers.

Animals↗
PubMed1982

Mutagenic responses of five independent genetic loci in CHO cells to a variety of mutagens. Development and characteristics of a mutagen screening system based on selection for multiple drug-resistant markers.

With the aim of developing a sensitive mutagen screening system, the responses of 15 different chemical mutagens at 5 independent genetic loci in Chinese hamster ovary (CHO) cells have been determined. The genetic markers which have been employed include resistance to thioguanine (Thgr), ouabain (OuaR), the protein synthesis inhibitor emetine (Emtr), the polyamine synthesis inhibitor methylglyoxal bisguanylhydrazone (Mbgr) and the nucleoside analog 5,6-dichlororibofuranosyl benzimidazole (DrbR). The optimal selection conditions for all of these genetic markers in CHO cells have been described. The chemicals whose response was investigated in these studies include direct-acting alkylating agents (ethyl methane-sulfonate, methyl methanesulfonate, beta-propiolactone, ethyleneimine, N-nitrosomethylurea and 4-nitroquinoline-N-oxide), DNA intercalating and cross-linking agents (ICR-170, acridine orange, ethidium bromide, mitomycin C and actinomycin D), polycyclic hydrocarbons (benzo[a]pyrene (B(a)P) and 7,12-dimethylbenz[a]anthracene (DMBA)) and aromatic amines (benzidine and beta-naphthylamine). Simultaneous examination of the response of the set of genetic markers to these chemicals revealed that although all of these chemicals caused a dose-dependent increase in the frequency of mutations at many of the above genetic loci, the magnitude of the mutagenic response at different genetic loci varied greatly depending upon the chemical. Of the genetic loci examined, no one single locus showed higher response to all of the above chemicals, instead, depending upon the chemical, specific loci were found to be more responsive than others. The polycyclic hydrocarbons and aromatic amines were weakly mutagenic in this system at several genetic loci even without any exogenous microsomal activation, although in the presence of a rat liver S9 fraction similar toxic and mutagenic effects of B(a)P and DMBA were observed at 5-20-fold lower concentrations. These results indicate that CHO cells may possess significant capacity for the metabolic activation of many procarcinogens, and also underscore the merits of measuring the mutagenic response at multiple genetic loci in mutagen screening studies.

Animals↗
PubMed1982

Novel orally active inhibitors of passive cutaneous anaphylaxis in rats: N-[2-(4-pyridinyl)-4-pyrimidinyl]ureas and dialkyl [[[2-(4-pyridinyl)-4-pyrimidinyl]amino]methylene]malonates.

4-Chloro-2-(4-pyridinyl)pyrimidines were treated with alkylamines to afford the corresponding N-substituted amino derivatives. 4-Amino-2-(4-pyridinyl)pyrimidines and their N-substituted analogues were converted to amides, carbamates, aminomethylenemalonates, and ureas. Many of these compounds were found to have potential antiallergic activity as indicated by the rat passive cutaneous anaphylaxis screen. The most compounds were found in the last two series.

Administration, Oral↗
PubMed1982

Characterization and cross-reactivity of human and mouse oncofetal antigens. Use of a new solid phase assay for detection of cell surface antigens.

Oncofetal (OF) antigens have been isolated from mouse F9 teratocarcinoma cells, mouse testicular cells, and human molar tissue by detergent extraction followed by dialysis. The soluble antigens have been used in solid phase radioimmunoassay (SPRIA) and enzyme-linked immunosorbent (ELISA) assay. Specific antibodies have been raised to these antigens in mice. By using these antisera, extensive cross-reactivity was found between mouse and human OF antigens. A human trophoblastic tumor cell line BEWO absorbed out mouse anti-F9 reactivity. Patients with tumors of germinal origin were found to have antibodies which cross-react with mouse and human OF antigens. This new assay is a rapid and sensitive method for the screening of monoclonal antibodies against these antigens as well as for detecting antibodies to tumors bearing these antigens in patients.

Absorption↗
PubMed1982

Ribonuclease E is involved in the processing of 5-S rRNA from a number of rRNA transcription units.

Strains of Escherichia coli having a thermosensitive RNase E produce a number of 5-S ribosomal RNA precursors at a non-permissive temperature. One of these precursors, 9-S RNA, was reported earlier [Ghora, B.K. and Apirion, D. (1978) Cell, 15, 1055-1066]. Here we show the existence of additional precursors to 5-S rRNA, originating from a number of rRNA genes. All the precursors are very similar in the first 200 nucleotides and the last part of this sequence contains the mature 5-S rRNA. Precursors that contain only these nucleotides (8-S RNA) accumulate. They probably originate from the rrn genes C, D and F which contain trailer tRNAs. The 9-S RNA precursors contain in addition a termination stem and loop structure and are derived from genes which do not contain trailer tRNA (Singh and Apirion, unpublished results). In addition, a 10-S precursor was identified. It contains distal to the 5-S rRNA a trailer tRNA, tRNAAsp, and a transcription termination signal. It is derived from the rrnF gene. The accumulation of an RNA precursor containing an RNase P site in an rne mutant suggests that the efficiency of one RNA processing enzyme depends on the activity of other RNA processing enzymes.

Base Composition↗