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Biomedical subjects

A K Chakravarty

Publications and source records attributed to A K Chakravarty.

At least 19 recordsLinked to original sources
PubMed2000

Bacopasaponins E and F: two jujubogenin bisdesmosides from Bacopa monniera.

Two new dammarane-type jujubogenin bisdesmosides, bacopasaponins E and F of biological interest have been isolated from the reputed Indian medicinal plant Bacopa monniera and defined as 3-O-[beta-D-glucopyranosyl(1 --> 3)[alpha-L-arabinofuranosyl(1 --> 2)]alpha-L-arabinopyranosyl]-20-O-(alpha-L-arabinopyranosyl) jujubogenin and 3-O-[beta-D-glucopyranosyl(1 --> 3)[alpha-L-arabinofuranosyl(1 --> 2)]beta-D-glucopyranosyl]-20-O-alpha-L-arabinopyranosyl) jujubogenin respectively by spectroscopic methods and some chemical transformations.

Diterpenes↗
PubMed1997

Characterization of primed lymphocytes on the basic of sensitivity of chromatin to DNase I.

Certain qualitative criteria for primed lymphocytes in the expression of cytotoxic function have been studied. Unlike normal lymphocytes, primed lymphocytes expressed cytotoxicity even when DNA synthesis and new gene expression were inhibited by hydroxyurea (HU) and bromodeoxyuridine (BU) respectively. Such differential cytotoxic expression in presence of HU and BU by primed lymphocytes might have their basis in conformational change within the chromatin. Chromatin from primed lymphocytes was more susceptible to DNase I digestion than virgin lymphocytes indicating exposition of more DNase I sensitive sites in primed state. The result suggest the presence of more ready to act sites for the polymerases in the genomic material of primed lymphocytes even at quiescent state.

Animals↗
PubMed1996

Amarogentin, a naturally occurring secoiridoid glycoside and a newly recognized inhibitor of topoisomerase I from Leishmania donovani.

A MeOH extract of Swertia chirata found to inhibit the catalytic activity of topoisomerase I of Leishmania donovani was subjected to fractionation to yield three secoiridoid glycosides: amarogentin (1), amaroswerin (2), and sweroside (3). Amarogentin is a potent inhibitor of type I DNA topoisomerase from Leishmania and exerts its effect by interaction with the enzyme, preventing binary complex formation.

Animals↗
PubMed1995

Iodoacetylated ouabagenins: their syntheses, spectroscopic characterizations, and stability studies.

Ouabain shows high binding ability to myocardial Na+,K(+)-ATPase and, therefore, a suitably radiolabeled derivative of this compound may find use in myocardial imaging. In this pilot experiment we report the preparation of several chloroacetylated and iodoacetylated ouabagenins. These intermediates may possess the potential for conversion to 99mTc-labeled tracer by a reported procedure with which the imaging of myocardial Na+,K(+)-ATPase may be possible. Appropriate analytical and spectroscopic data for these intermediates are reported for the first time. To determine the stability of the iodoacetylated ouabagenins, corresponding 131I derivatives were synthesized which showed sufficient stability for incorporating a suitable radiometal-binding chelating moiety to these steroid molecules.

Acetylation↗
PubMed1994

Immunofluorescence analysis of immunoglobulin bearing lymphocytes in the Indian fruit bat: Pteropus giganteus.

The immunologic cell types of the Indian fruit bat, P. giganteus, were characterized on the basis of cell surface Ig markers. Rabbit anti-rat IgM and IgG demonstrated IgM or IgG bearing cells in the nylon wool adherent lymphocyte population, thereby suggesting their equivalence to the B cells of recently evolved mammals including man. Relative proportion of these Ig+ surface bearing cells was about one-half of the bone marrow lymphocytes, one-third of mesenteric lymph node lymphocytes, and two-thirds of the splenic and peripheral blood lymphocytes. Considering the early origin of Megachiropters (fruit bats) in mammalian evolution, it is suggested that surface characteristics of typical mammalian lymphocytes like Ig markers as such or as genomic messages existed at the time of evolution of Class Mammalia. The high percentage of surface Ig+ cells in the peripheral circulation of bats suggests a "natural immunodeficiency state", which may be equivalent to immunodeficiency state in humans.

Animals↗
PubMed1992

Central histaminergic involvement during stress in rats.

Effects of some drugs modulating central histaminergic (HA) transmission were evaluated on restraint stress (RS)-induced gastric ulcerogenesis, plasma corticosterone and immune responses in rats. RS for (i) 6 hr or (ii) 24 hr at room temperature, and (iii) 3 hr at 4 degrees C (CRS) all induced gastric mucosal erosions and elevated plasma corticosterone levels, the effects with the latter two RS procedures being most consistent. Pretreatment of rats with neuronal HA depletor, alpha-FMH (100 mg/kg, ip) attenuated both ulcer severity and corticosterone response, during both 24 hr RS and CRS. Similar effects were also seen with the mast cell degranulator, C-48/80 (10 micrograms/kg, i.c.v.) treatment. Further, the H1-blocker, pheniramine (25 mg/kg, ip) but not the centrally acting H2-blocker, zolantidine (5 mg/kg, ip) produced clearcut attenuations in both stress markers, during the experimental stressors. In rats immunized in SRBC, 24 hr RS (and not CRS) significantly prevented the humoral immune responses to the antigen. alpha-FMH, C 48/80 and pheniramine but not zolantidine, reversed this response during 24 hr RS. The results indicate a central HA ergic involvement in the visceral, endocrinal and immune responses during RS and suggest the probable role of both neuronal as well as extraneuronal (mast cell) HA and activation of H1-receptors in the mediation of these effects.

Animals↗
PubMed1991

Role of histaminergic mechanisms in the regulation of some stress responses in rats.

The involvement of histaminergic mechanisms in the regulation of some stress responses was studied in rats. The brain neuronal histamine (HA) depletor, alpha-fluoromethyl histidine (alpha-FMH), at doses (50 or 100 mg/kg) which markedly lower brain HA, significantly attenuated the gastric ulcer formation and the elevation in plasma corticosterone in response to cold restraint stress (CRS). alpha-FMH also appreciably reduced gastric mucosal HA content. The H1-antagonist, pheniramine (25 mg/kg), attenuated both the gastric mucosal and endocrine response to CRS, while the effects of the H2-antagonist, cimetidine (200 mg/kg), were on the plasma corticosterone levels. These results are discussed in light of complex HA-ergic mechanisms in the maintenance of physiological homeostasis during stress.

Animals↗
PubMed1991

Analysis of immunocompetent cells in the bat, Pteropus giganteus: isolation and scanning electron microscopic characterization.

Immunocompetent cells of the Indian fruit bat (P. giganteus) were characterized by differential surface adhesiveness and surface topography. We observed three cell types: (1) plastic adherent with pseudopodia; (2) nylon wool adherent with small microvilli and pits; and (3) a nylon wool nonadherent with comparatively smooth surfaces. These cell types resemble, respectively, macrophages, B cells and T cells of other mammals, including mice and humans. The disposition of microvilli on the B-type cell surface changes significantly after immunization, which suggests modulation of the molecular organization of the cell membrane and its fluidity. The proportions of these three cell types are not much different from those found in mice. Follicular dendritic cells, capable of retaining antigen for long periods in mice, have also been detected in bats. Further characterization of immunocompetent cells wil help in understanding the mechanism of immune responses in bats.

Animals↗
PubMed1991

Effects of some imidazoles on cellular immune responses--an experimental study.

Effects of some imidazole compounds were studied on two animal models of cellular immune responses. Metronidazole in doses of 100 and 200 mg/kg and cimetidine 200mg/kg (ip), significantly suppressed the delayed type of hypersensitivity reaction, as evidenced by the footpad thickness method in mice. No significant alteration in the response could be observed however, in tinidazole treated groups. All the three drugs inhibited the migration of leucocytes in the presence of antigen in rats considerably. However, they did not produce any involution of spleen or reduction of adrenal weight indicating that their actions are not corticosteroid mediated. All the three drugs studied are histamine-like imidazole derivatives. H2 receptors are present on the surface of T-lymphocytes. They appear to modulate the cellular immune response by altering the function of the regulatory lymphocytes.

Animals↗
PubMed1990

Incapacitation of fibrosarcoma cell by polyclonally activated murine T cell.

A piece of lymph node containing polyclonally-activated lymphocytes when transplanted in the anterior eye chamber of mouse along with solid piece of fibrosarcoma from syngeneic Swiss mice, dramatically inhibited the tumour-induced-vasodilatation and neo-vascularization. If the tumour explants were incubated in vitro with activated lymphocytes prior to transplantation, such angiogenic reactions was significantly reduced. These explants were incapable of incorporating radioactive thymidine in vitro. Furthermore, the cytotoxic ability of activated lymphocytes towards 51Cr labelled tumour target cells was of significant level indicating the possible mechanism of immunological reactiveness of Con A-stimulated lymphocytes to 3'-methylcholanthrene-induced tumour cells of syngeneic origin.

Animals↗
PubMed1987

Analysis of suppressor factor in delayed immune responses of a bat, Pteropus giganteus.

Bat spleen and mesenteric lymph node cell cultures treated with varying doses of LPS showed significant blastogenic and DNA synthetic responses between 72-96h. Peak responses were not different when the cell culture medium was supplemented either with autologous serum or heterologous serum indicating the absence of any significant suppressor factor in autologous bat serum. In contrast, blastogenesis and DNA synthesis peaks appeared early, at 48h, in lymphocytes depleted of suppressor T cells by pretreatment with cyclophosphamide. Direct antibody producing cells against SRBC were studied in normal spleen and mesenteric lymph node cell cultures. The peak PFC response was lacking even at 120h while CY pretreated bat lymphocytes, showed peak PFC responses at 96h. Thus the delayed immune response in bats seems to be a function of suppressor T cells but serum suppressor factor(s) possibly exerts no significant effect. The function of suppressor cells in bats in relation to their role as carriers of several dreaded bacteria and viruses is discussed.

Animals↗
PubMed1986

In vitro analysis of delayed immune response in a bat, Pteropus giganteus: process of con-A mediated activation.

In vitro activation of lymphocytes from the bat, Pteropus giganteus with Con A has been analysed in terms of blastogenesis, DNA synthesis and the effector function, the cytotoxic response. We have observed that lymphocytes of P. giganteus are capable of responding to Con A stimulus and the peak of blastogenesis, DNA synthesis and cytotoxic response have been found at 120 hours with the optimal dose of 10 micrograms X ml-1 Con A; it seems the process of activation in the bat's lymphocytes is delayed compared to this in mice. Significance of this delay in the process of activation of immune response in the bat has been discussed.

Animals↗
PubMed1986

Activation of murine thymocytes in vivo. Part II: Study of blastogenesis, the synthesis of macromolecules and the cytotoxic response after stimulation with phytohemagglutinin.

To determine whether the polyclonal immunomodulator, Phytohemagglutinin (PHA), stimulates murine lymphocytes in vivo and causes cytotoxic differentiation, we studied blastogenesis and the concomitant synthesis of macromolecules (DNA, RNA and protein) by lymphocytes at different hours after injection of PHA in mice. 51Cr release assay was also performed by using allogeneic cells as target to determine whether lymphocytes after stimulation in vivo by this activator undergo cytotoxic differentiation. Out of the five doses of Phytohemagglutinin (2.5 micrograms, 5 micrograms, 10 micrograms, 20 micrograms and 50 micrograms per mouse) a marginally higher peak of blastogenesis was observed with 20 micrograms dose at 48 hr. No significant peak was observed in synthesis of macromolecules or with cytotoxicity.

Animals↗