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Biomedical subjects

T Ramakrishnan

Publications and source records attributed to T Ramakrishnan.

At least 19 recordsLinked to original sources
PubMed1996

Antral atrophy, Helicobacter pylori colonization, and gastric pH.

The association between the topographic distribution of Helicobacter pylori colonization, inflammation and atrophy of the gastric mucosa, and fasting gastric pH was studied in a population with high prevalence of multifocal atrophic gastritis. Increasing atrophy of the antrum was associated with decreasing H pylori colonization of the antrum itself, but increasing colonization of the corpus. Advanced atrophy was associated with high fasting gastric pH. However, after therapeutic eradication of H pylori, inflammation subsided and gastric pH decreased indicating improved acid secretion despite persistent atrophy. The authors propose that antral atrophy fosters the colonization of oxyntic mucosa by H pylori, thus impairing acid secretion and causing hypochlorhydria that may further promote colonization of the oxyntic mucosa. Eradication of H pylori significantly improves hypochlorhydria. It may restore acid secretion in most patients, regardless of the presence of atrophy, which is an effect that may be of great benefit in halting the process of gastric carcinogenesis.

Adult↗
PubMed1994

Ascorbic acid, Helicobacter pylori and Lewis phenotype among blacks and whites in New Orleans.

Gastric juice ascorbic acid concentrations were examined in black and white patients. Significantly lower concentrations were found in blacks, in the absence of a significant difference in the plasma concentration of vitamin C between races. Blacks had higher prevalence of Helicobacter pylori infection, higher gastric pH, more severe acute and chronic inflammation of the gastric mucosa and higher frequency of Lewis (a-b-) phenotype. Although most of these factors have been related to low ascorbic acid levels in gastric juice, none of them could account entirely for the difference between races either individually or after joint consideration. These observations may help to explain the high incidence of gastric carcinoma among the black population in southern Louisiana.

Ascorbic Acid↗
PubMed1993

The rheumatoid factor cross-reactive idiotype in juvenile rheumatoid arthritis: role of the CD5-positive B cell.

The major rheumatoid factor cross-reactive idiotype (RCRI), which was defined by prototypic monoclonal IgM rheumatoid factors (RF) from Waldenstrom's macroglobulinemia patient Wa, is present on 60% of all monoclonal IgM RF paraproteins. The RCRI is expressed in high frequency by pokeweed mitogen-derived plasma cells (PWM-PCs) and in high concentration in the sera from adults with rheumatoid arthritis (RA) who express RF in their sera. Unlike adults with RA, most children with juvenile rheumatoid arthritis (JRA) are seronegative for RF as detected by classic IgG binding assays. In the experiments summarized herein, we demonstrated that approximately 2/3 of JRA patients who are seronegative for RF, express the RCRI in high concentration in their sera and in high frequency among their PWM-PCs. Expression of this idiotype could not be attributed to expression of hidden IgM RF, or IgA RF, and may be expressed on a parallel set of immunoglobulin molecules, related to RFs, but lacking the ability to bind to IgG. There is an increased number of circulating CD5+ B cells in patients with JRA but there was no significant relationship between CD5+ B cell numbers and serum RCRI concentration, suggesting that in this disease, RCRI bearing immunoglobulins may also be produced by non-CD5+ B cells or by a small subset of CD5+ B cells.

Adolescent↗
PubMed1991

Hidden rheumatoid factor and Wa idiotype expression in juvenile rheumatoid arthritis.

The major rheumatoid factor cross-reactive idiotype, which was defined by prototypic monoclonal IgM rheumatoid factors from Waldenstrom's macroglobulinaemia patient Wa, is present on 60% of all monoclonal IgM RF paraproteins. One-third of patients with juvenile rheumatoid arthritis (JRA), who are seronegative for classic IgM rheumatoid factor (RF), express the Wa idiotype in high titre in their sera. To determine if the Wa idiotype is present on hidden rheumatoid factors in JRA patient sera, we studied hidden RF expression by both ELISA and haemolytic assay techniques. The majority of JRA sera with increased concentrations of the Wa idiotype did not have increased RF activity nor hidden RF activity. In some JRA patients, the Wa idiotype may be expressed on a parallel set of immunoglobulin molecules, related to RFs, but lacking the ability to bind to IgG.

Adolescent↗
PubMed1988

Detection of the major rheumatoid factor cross-reactive idiotype precedes human IgG binding activity in a patient with polyarticular juvenile rheumatoid arthritis.

A patient with polyarthritis and subcutaneous nodules was studied for expression of rheumatoid factors (RF) by numerous techniques for 5 months after presentation. Assays for RF binding human or rabbit IgG in whole sera, assays for hidden RF binding human or rabbit IgG, and assays for expression of the major RF cross-reactive idiotype (RCRI) in whole sera or by pokeweed mitogen induced plasma cells were performed (PWM-PC). In this patient, increased expression of RCRI in sera and among PWM-PC preceded detectable RF binding human IgG, and paralleled hidden RF and RF binding rabbit IgG expression.

Adolescent↗
PubMed1986

Deoxyribonucleic acid replication time in Mycobacterium tuberculosis H37 Rv.

The DNA increment method, designed for measuring the increment in the amount of DNA after inhibition of initiation of fresh rounds of replication initiation was employed to measure the rate of deoxyribonucleic acid (DNA) chain growth in Mycobacterium tuberculosis H37Rv growing in Youman and Karlson's medium at 37 degrees C with a generation time of 24 h and also in relatively fast growing species like Mycobacterium smegmatis and Escherichia coli. From the results obtained, the time required for a DNA replication fork to traverse the chromosome from origin to terminus (C period) was calculated. The chain elongation rates of DNA of the three organisms was determined from the C period and the known genome sizes assuming that all these genomes have a single replication origin and bidirectional replication fork. The rate for M. tuberculosis was 3,200 nucleotides per min about 11 times slower than that of M. smegmatis and about 13-18 times slower than that of E. coli.

Chloramphenicol↗
PubMed1984

Nucleotide sequence of initiator tRNA from Mycobacterium smegmatis.

The nucleotide sequence of initiator tRNA from Mycobacterium smegmatis was determined to be pCGCGGGGUGGAGCAGCUCGGDAGCUCGCUGGGCUCAUAACCCAGAGm7GUCG CAGGU psi CGm1AAUCCUGUCCCCGCUACCAOH . The nucleotide sequence of Mycobacterium initiator tRNA was found to be the same as that of Streptomyces initiator tRNA, except that G46 and A57 were replaced by m7G46 and G57 , respectively. The striking feature of Mycobacterium initiator tRNA is the absence of ribothymidine at residue 54, and the presence of 1-methyladenosine at residue 58 which makes the sequence of this tRNA similar to that of eukaryotic initiator tRNA.

Adenosine↗
PubMed1981

Purification and properties of DNA polymerase from Mycobacterium tuberculosis H37Rv.

DNA polymerase has been purified approximately 2000-fold from Mycobacterium tuberculosis H37Rv. The purified preparation was homogeneous by electrophoretic criteria and has a molecular weight of 135 000. The purified enzyme resembles Escherichia coli polymerase I in its properties, being insensitive to sulfhydryl drugs and possessing 5',3'-exonuclease activity in addition to polymerase and 3',5'-exonuclease activities. However, it differs from the latter in its sensitivity to higher salt concentration and DNA intercalating agents such as 8-aminoquinoline. The polymerase exhibited maximal activity between 37--42 degrees C and pH 8.8--9.5. The polymerase was stable for several months below 0 degree C. However, the 5',3'-exonuclease activity was more labile. The effects of different metal ions, polyamines and drugs on the polymerase activity are presented.

DNA-Directed DNA Polymerase↗
PubMed1981

Deoxyribonucleic acid methylation in mycobacteria.

Deoxyribonucleic acid modification in six strains of mycobacteria was investigated. The presence of 5-methylcytosine in the virulent strain Mycobacterium tuberculosis H37Rv and its absence in the avirulent strain M. tuberculosis H37Ra and other saprophytic, fast-growing mycobacteria appear to be the salient features. However, deoxyribonucleic acid from M. smegmatis SN2 lysogenized with the temperature phage I3 showed the presence of 5-methylcytosine. All of the strains had N6-methyladenine.

5-Methylcytosine↗
PubMed1979

Adynamic ileus complicating colonoscopy.

A case of adynamic ileus of the colon and small bowel complicating colonoscopy is reported. The patient recovered with conservative management. Possible pathogenesis of this rare complication is discussed.

Colon↗
PubMed1979

Occurrence of 1-methyladenosine and absence of ribothymidine in transfer ribonucleic acid of Mycobacterium smegmatis.

The minor base composition of Mycobacterium smegmatis tRNA has been studied. Thin-layer chromatographic patterns of a ribonuclease T2 digest of mycobacterial tRNA indicated the presence of appreciable amounts of 1-methyladenosine (which is commonly present only in eucaryotic tRNA), dihydrouridine, and 7-methylguanosine. Ribothymidine was absent. The S-adenosylmethionine-dependent tRNA methylases of M. smegmatis catalyzed the formation of 1-methyladenosine when Escherichia coli tRNA was used as acceptor. Similarly, E. coli extracts methylated the tRNA of M. smegmatis, forming ribothymidine.

Adenosine↗