Volume 14, Issue 1
March 1989, pages 1-67
pp 1-7 March 1989
Short term effects of ovulen-50, a combination type oral contraceptive agent and phenobarbital—an established hepatic tumour promoter, were examined in the livers of diethylnitrosamine-initiated and uninitiated female rats. Liver mitotic activity as judged by liver weight, [3H] thymidine incorporation into DNA and levels of DNA, RNA and protein were measured in non-regenerating and regenerating liver. Hepatic γ-glutamyl transpeptidase activity and hepatocyte agglutination with concanavalin A were examined in diethylnitrosamine- and/or phenobarbital-treated rats.
The results indicate that diethylnitrosamine or ovulen-50 individually are mitoinhibitory in regenerating liver. Phenobarbital alone has a slight mitostimulatory effects in non-regenerating liver, but no effect on liver regeneration. Administration of ovulen-50 and phenobarbital to diethylnitrosamine initiated rats mitigated the mitoinhibition during regeneration. Contrary to the earlier observation with ovulen-50, neither phenobarbital nor diethylnitrosamine induced hepatocyte agglutination in the presence of concanavalin A. Like ovulen-50, diethylnitrosamine also increased the level of hepatic γ-glutamyl transpeptidase. Phenobarbital produced only insignificant rise and did not substantially exacerbate the effect diethylnitrosamine.
The data show that though some of the effects of ovulen-50 resemble those of diethylnitrosamine or phenobarbital, the changes observed may not be related to the neoplastic phenomenon since they were not seen in an initiator-promoter combination regimen.
pp 9-20 March 1989
A method has been developed for immobilisation of antisera on fresh plastic tubes through an immunochemical bridge. This type of immobilisation has been shown to be more consistent than direct adsorption on plastic. Such immunochemically coated antisera on plastic tube has been used in the development of a noncentrifugation radioimmunoassay. This assay system has been found to be technically as sound as the conventional method.
pp 21-27 March 1989
Biochemical characteristics of bi-resistant mutants (resistant to ethambutol plus streptomycin or isoniazid plus streptomycin) of mycobacteria isolated by replica plating fromMycobacterium smegmatis ATCC were compared with those of the drug-susceptible strains. Reduced incorporation of [14C]uracil, [3H]lysine and [14C]acetate into RNA, protein and phospholipids respectively was seen in the resistant mutants. Total phosphorlipids were enhanced in ethambutol plus streptomycin resistant mutant and decreased in isoniazid plus streptomycin resistant mutant. There were similar changes in levels of individual phospholipids. The resistant mutants revealed an accumulation of phospholipids in the cell wall, and a marked decrease of phospholipids in the cell membrane in comparison to the susceptible strain. Several qualitative alterations in the polypeptide profile (with respect to number and molecular weight) of the crude protein extract and of different subcellular compartments were seen in the resistant mutants.
pp 29-36 March 1989
Recent studies in basic immunology have been directed towards the understanding of the mechanism of T cell activation. T cells can be activated to proliferatevia the classical pathway through the antigen receptor (CD3-Ti) orvia the alternate pathway through the CD2 receptor. Since immunologic unresponsiveness in lepromatous leprosy is considered to be due to the inability of T cells to proliferate upon stimulation, we have been interested in the nature of these receptors and the activation pathways in lymphocytes of leprosy patients. In the present investigation we demonstrate: (i) CD2 receptor (E-receptor) is downregulated in bacterial index positive lepromatous leprosy patients. (ii) The alternate pathway of T cell activation is impaired in lepromatous patients as revealed by the inability of their lymphocytes to proliferate in response to a pair of mitogenic anti-CD2 monoclonals. (iii) The addition of recombinant interleukin 2in vitro restores the ability of lymphocytes from lepromatous patients to proliferate in response to anti-CD2 antibodies. (iv) Interestingly, CD2 modulation and the associated functional impairment could be brought about in peripheral blood lymphocytes from normal subjects by prior treatment withMycobacterium leprae in vitro. This approach would be useful in understanding the molecular events leading to the defective T cell functions in leprosy.
pp 37-45 March 1989
The viability ofMycobacterium leprae, maintained within 33B Schwannoma cells, was estimated in terms of incorporation of [14C] acetate into its specific phenolic glycolipid-1. This measure of viability was correlated with two other assays,viz., fluorescein diacetate/ethidium bromide staining and mouse footpad growth. Observation of a 2-fold increase in the number of intracellularMycobacterium leprae over an experimental period of 12 days also corroborated this contention. Furthermore, on addition of anti-leprosy drugs to these intracellularMycobacterium leprae there was significant decrease in phenolic glycolipid-1 synthesis indicative of loss of viability of the organisms. This study also established the importance of the host cell for active bacillary metabolism, asMycobacterium leprae maintained in cell-free conditions showed no incorporation into phenolic glycolipid-1. Moreover, compromising the host’s protein synthesis capacity with cycloheximide, also led to reduction in bacillary metabolism. As this system measures the metabolic synthesis of a uniqueMycobacterium leprae component, it would be useful for development and screening of compounds acting against specific bacillary targets.
pp 47-54 March 1989
Phosphoglucoisomerase from cytosol of immature wheat endosperm was purified 650-fold by ammonium sulphate fractionation, isopropyl alcohol precipitation, DEAE-cellulose chromatography and gel filtration through Sepharose CL-6B. The enzyme, with a molecular weight of about 130,000, exhibited maximum activity at pH 8.1. It showed typical hyperbolic kinetics with both fructose 6-P and glucose 6-P withKm of 0.18 mM and 0.44mM respectively. On either side of the optimum pH, the enzyme had lower affinity for the substrates. Using glucose 6-P as the substrate, the equilibrium was reached at 27% fructose 6-P and 73% glucose 6-P with an equilibrium constant of 2.7. The ΔF calculated from the apparent equilibrium constant was +597 cal mol-1. The activation energy calculated from the Arrhenius plot was 5500 cal mol-1. The enzyme was completely inhibited by ribose 5-P, ribulose 5-P and 6-phosphogluconate, withKi values of 0.17, 0.25 and 0.14 mM respectively. The probable role of the enzyme in starch biosynthesis is discussed.
pp 55-61 March 1989
Chronic administration of ethanol in rats caused the reduction of serum cholesterol binding reserve. The very low density and high density lipoproteins, main serum cholesterol binding reserves, were slightly increased with corresponding increases in their lipid and protein components during initial stage of alcohol consumption. However, these capacities get deminished during reversal of hyperlipemia induced by prolonged action of ethanol. This situation may be an early indicator for the initiation of hepatic damage and a variety of secondary effects of ethanol.
pp 63-67 March 1989
Changes in GABA content of various brain areas during different stages of picrotoxin-induced seizures and following pretreatment with the anti-convulsants phenobarbital andγ-acetylenic GABA were studied. Picrotoxin (6mg/kg) produced clonic/tonic convulsions associated with a 34% reduction in GABA content of the sensory motor cortex. A reduction of 24% was observed 1 min before the onset of seizure and the reduction in GABA content was reversible 20 min after the convulsion. No significant changes were observed in the cerebellum or spinal cord/medulla oblongata. Pretreatment with phenobarbital (100mg/kg) delayed the onset of convulsion and decreased the mortality rate without causing any change in GABA content at the pre-convulsive, convulsive or post-convulsive stages.γ-Acetylenic GABA (100mg/kg) has elevated GABA levels in different areas of the brain by 2–3-fold after 60 min treatment. This increase was reduced by 44% during the onset of picrotoxin-induced seizures. Picrotoxin convulsion can occur in the presence of normal, reduced or even elevated brain GABA content. The only consistent factor is a one-third reduction in GABA content before the onset of seizure.