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Biomedical subjects

S Majumdar

Publications and source records attributed to S Majumdar.

At least 307 records · Page 17Linked to original sources
PubMed1987

Effect of vasectomy on humoral and cell-mediated immunity in monkeys with experimentally induced atherosclerosis.

The development of humoral and cell-mediated immune responses and circulating immune complexes following vasectomy were studied in rhesus monkeys fed a high cholesterol (atherogenic) diet. Four groups of monkeys were studied: (i) sham-vasectomized males fed a normal stock diet, (ii) sham-vasectomized males fed an atherogenic diet, (iii) vasectomized males fed a normal stock diet, and (iv) vasectomized males fed an atherogenic diet. Monkeys were observed for a period of 1.5 years. Sperm agglutinins and immobilizins in serum were detected in 100 and 60%, respectively, of vasectomized monkeys fed stock diet. In contrast, 60% of vasectomized monkeys fed an atherogenic diet showed agglutinins in their sera and only 20% exhibited immobilizins. The sensitization of lymphocytes by seminal plasma antigens was of a lower order in vasectomized monkeys fed an atherogenic diet as compared to those maintained on a stock diet. Circulating immune complexes (CIC) were present in both the groups of vasectomized monkeys but the level was higher in animals fed an atherogenic diet. The aortic atherosclerosis score was increased significantly in vasectomized monkeys fed an atherogenic diet, whereas the coronary atherosclerosis score was increased both in vasectomized males and in animals fed an atherogenic diet.

Animals↗
PubMed1987

Mutual and self-sensitivity among antibiotically active mutant derivatives from the inactive degenerate Aspergillus versicolor N5.

Antibiotically active producer mutants derived from the spontaneous degenerate parent Aspergillus versicolor N5 possessed not only mutual but also self-sensitive activity. The producer mutants, like the inactive parent, were only 3.5-fold less sensitive than the most sensitive unrelated organism, Trichophyton rubrum. The germination of spores is generally more sensitive than growth of vegetative cells. The antifungal spectrum of these mutual and self-sensitive mutants was fairly wide, unlike the host range specificity of bacteriocinogenic strains acting on organisms closely related to the producers. The self and mutual growth inhibitory principle was finally identified as the antibiotics mycoversilin and versilin in the case of producer mutants (N5)17 and N5T10(7), respectively, or Vx, an antibiotic of unknown molecular species, in the case of another producer mutant N5T10(8). Thus self-sensitivity, instead of self-resistance, of these antibiotically active mutant derivatives is a unique property among filamentous fungi in having simultaneously expressed two loci of contradictory functions, one for synthesis of, and the other for sensitivity towards, the same or related antibiotics.

Antifungal Agents↗
PubMed1987

Physico-chemical interaction of mycobacillin with Aspergillus niger protoplast membrane, the site of its action.

Mycobacillin partially quenched the strong fluorescence when 1-anilino naphthalene 8-sulfonate (ANS) was added to protoplast or plasma membrane but is without any effect on weak fluorescence when added to cell-free extract. There are two classes of ANS binding sites on protoplast or plasma membrane of which one class is sensitive to mycobacillin, being competitively abolished by it. Mycobacillin also non-competitively inhibits the binding of pyrene, a lipid specific probe. Thus it follows from the inhibition by mycobacillin of ANS or pyrene binding to protoplast or plasma membrane that the site of action of the antibiotic is located in the plasma membrane. Interaction between mycobacillin and the plasma membrane is physico-chemical in nature.

Anilino Naphthalenesulfonates↗
PubMed1987

Phospholipid dependence of rat brain microsomal glucose-6-phosphate phosphohydrolase.

Partial lipid removal of rat brain microsomes by acetone-butanol extraction resulted in 32% loss of activity of glucose-6-phosphate phosphohydrolase (G-6-Pase) and an increase in Km and energy of activation (Ea) of the enzyme while the Vmax was lowered. The activity was restored by supplementation of microsomal total phospholipid (PL) and phosphatidylcholine (PC) in sonicated dispersions but not with neutral lipids, phosphatidyl ethanolamine, sphingomyelin, phosphatidylglycerol and cholesterol. In both intact and delipidated membranes, the activity was decreased by sodium deoxycholate and enhanced by dimethylsulfoxide. Egg yolk PC and asolectin influenced the activity to the extent of that produced by microsomal PC. PC increased the Km of the enzymatic reaction in intact microsomes but decreased the same in disrupted membrane while the Vmax was not affected in both the membranes. Addition of PC into the assay system lowered Ea of the reaction in both the membrane systems. However, there was no break observed in the Arrhenius plot. Ability of liver nonspecific lipid transfer proteins to introduce alien PL into brain microsomes was used to study lipid dependence of G-6-Pase and investigation of membrane-enzyme interrelationship. Protein catalyzed transfer of egg PC from a donor PC-cholesterol unilamellar liposomes resulted in substantial increase in microsomal membrane PC and total PL and a net reduction in the enzyme activity was observed in intact and delipidated membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Isolation of monkey aortic lysosomes using Percoll density gradient.

A novel technique involving the Percoll density gradient and 0.01M phosphate buffer has been employed for the first time on aortic tissue for isolation of lysosomes. The purity of the lysosomes has been established by marker-enzymes, acid phosphatase and N-acetyl-beta-D-glucosaminidase and latent activities of lysosomal hydrolases. The heavier fraction (density 1.08) obtained after Percoll density gradient centrifugation showed high specific activities of lysosomal hydrolases and these enzymes were markedly latent. Moreover this heavier (lysosome rich) fraction has been noted to be free of other sub-cellular contaminants.

Acetylglucosaminidase↗
PubMed1986

Selective action of mycobacillin on the uptake of releasable cell materials by Aspergillus niger.

The uptake of normally releasable (i.e. releasable in the absence of the antibiotic) cell constituents (namely lysine, proline, ATP, Pi, Na+, K+ and Ca2+) by sensitive cells of Aspergillus niger that occurs in the absence of mycobacillin is gradually enhanced with increase in concentration of the antibiotic until the uptake attains the maximum. With still higher concentrations the uptake decreases until it becomes the same as in the control without mycobacillin. Uptake follows saturation kinetics both in the absence and in the presence of the antibiotic. Mycobacillin significantly increases Vmax. for uptake with any effect on Km, Mycobacillin has no action on the uptake of non-releasable materials.

Adenosine Triphosphate↗
PubMed1986

Errors in the measurements of T2 using multiple-echo MRI techniques. I. Effects of radiofrequency pulse imperfections.

In principle, multiple-echo magnetic resonance imaging (MRI) can be used to estimate the spin-spin relaxation time, T2, which can then be used for quantitative tissue characterization. Although multiple echoes can be used to enhance the signal-to-noise ratio in an image, by echo addition, rf pulse imperfections modify the echo amplitudes resulting in significant errors in the estimate of T2. Imperfect 180 degree pulses do not completely invert the transverse magnetization so that the magnitude of the transverse component is reduced and a longitudinal component is generated. Successive application of such imperfect pulses generates many components that interact in a complex manner. The amplitudes of successive echoes are affected whenever the transverse components refocus, whereas the longitudinal components may be rotated into the transverse plane by subsequent pulses and may often add to the image signal or give rise to an image artifact. These effects have been analyzed theoretically and have been demonstrated for a wide range of rf pulse imperfections using both simple and composite pulses, through computer simulations based on the numerical solution of the Bloch equations. The theoretical and simulation results have been substantiated through experiments performed on a mineral oil phantom using a resistive prototype MR scanner operating at 6.35 MHz. In this paper we report the effects of improper pulse amplitude or duration for nonselective rf pulses on resonance. We separately describe the other types of imperfections caused by off-resonance effects and the use of selective pulses.

Humans↗
PubMed1986

Errors in the measurements of T2 using multiple-echo MRI techniques. II. Effects of static field inhomogeneity.

The accurate estimation of the spin-spin relaxation time T2 is an important goal in magnetic resonance imaging particularly because it can be used for quantitative tissue characterization. The spin-spin relaxation time T2 may be estimated using multiecho pulse sequences, but the accuracy of the estimate is dependent on the fidelity of the spin-echo amplitudes, which may be severely compromised by rf pulse and static field imperfections. In this paper, the effects of static field inhomogeneities are investigated. The propagation of the errors introduced by off-resonance effects are analyzed through computer simulations and analytical solutions of the Bloch equations. A series of experiments performed on a simple tissue phantom using a whole-body imaging system operating at 6.35 MHz corroborates the simulation and analytical results. For accurate measurements of T2 using a whole-body imaging system it is necessary to correct for these inhomogeneities. A correction scheme which would enable a more accurate estimate of T2 is currently under investigation.

Biometry↗
PubMed1986

Relationship between sporulation and synthesis of mycobacillin and dipicolinic acid under condition of catabolite repression in Bacillus subtilis.

Sporulation was repressed in the parent strain by various carbon sources whereas glucose-resistant mutants were resistant to them but not to glycerol 2-phosphate. Both mycobacillin and dipicolinic acid synthesis were repressed in the parent by some of the compounds tested, viz. glucose, pyruvate and glycerol 2-phosphate. However, these syntheses in the glucose-resistant mutants were not repressed by glucose and pyruvate but were repressed by glycerol 2-phosphate. The possible interrelationship between sporulation, dipicolinic acid and mycobacillin synthesis is discussed in light of these findings.

Antifungal Agents↗
PubMed1986

Pathological changes in fallopian tubes following three different kinds of occlusive techniques in primates.

A comparative evaluation of three different techniques (Madlener's, Wood's and Filshie Clip Mark IV) for female sterilization was carried out in adult female rhesus monkeys with the aim of finding out the efficacy and the extent of tissue damage in the fallopian tube. The severity of pathological changes would indicate the chances of future successful reversal. The experiment was carried out in two phases. In Phase-I, no post-operative antibiotics were given whereas in Phase-II in addition to post-operative antibiotics, two sham-operated controls were also kept. This study revealed that the Filshie's clip is associated with significantly (p less than 0.01-0.001) greater tissue damage of the fallopian tubes with formation of dense adhesions as compared to the Madlener's or Wood's technique. Further, Filshie's clip had slipped off from 4 tubes out of 14 tubes where it was applied.

Animals↗
PubMed1986

Long term effects of vasectomy on experimental atherosclerosis in rhesus monkeys.

Five groups of male rhesus monkeys, Gp. I--sham-vasectomized stock diet-fed (SVS), Gp. II--vasectomized stock diet-fed (VS), Gp. III--sham-vasectomized atherogenic diet-fed (SVA), Gp. IV--vasectomized atherogenic diet-fed (VA) and Gp. V--atherogenic diet-fed vasectomized monkeys (AV) were observed for a period of 1 1/2 years. Vasectomy per se had no effect on the level of serum or tissue lipids either alone or in combination with atherogenic diet feeding. Following vasectomy the involvement of aorta by fatty lesions was significantly increased and this occurred in animals of all four experimental groups when compared with the control animals. The maximum increase was noted in group IV. Again, there was a significant increase in the frequency of aortic plaques in groups II, III and IV while it was increased in coronary arteries of all the experimental animals (Gps. II, III, IV and V). Group IV monkeys showed higher frequency of plaques as compared to group V animals. Although the plaque height was increased in all the vessels of the experimental animals, significant differences were observed only in the coronary arteries of group II monkeys and in intra-cranial cerebral vessels of group III animals. This study shows that vasectomy per se tends to increase atherosclerosis in rhesus monkeys.

Animals↗
PubMed1986

Role of selective pressure by screening organisms in the development of producer mutant isolates of different antibiotic markers.

The phenotypes of producer mutant isolates when obtained after mutagenesis of the spontaneous degenerate Aspergillus versicolor N5 by screening on Trichophyton rubrum and those on A. niger G3Br were found to be markedly different. In respect of phenotypic character anti-T. rubrum producer mutant isolates resembled the parental type more closely (which is specifically active against T. rubrum and generally against dermatophytes) than anti-A. niger mutant isolates. This clearly indicates not only the role of selective pressure of the screening organism in the development of a given producer mutant isolate but also shows the possibility of recovery of a producer type of the lost antibiotic marker.

Anti-Bacterial Agents↗