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Query: UMLS:C0011570 (depression)
 172,036 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The relationship of polyamine accumulation and semiconservative DNA replication was studied in synchronous Chinese hamster ovary cultures, progressing through the cell cycle either normally at 37 degrees or after hyperthermic exposure (43 degrees for 1 hr) during G1 or S phase. In control cultures, intracellular polyamine levels decreased as cells divided and then reaccumulated as cells exited G1 and proceeded through the S and G2 phases. Immediately after cultures were exposed to 43 degrees heat for 1 hr in G1 phase, intracellular levels of spermidine and spermine were reduced compared to controls. Coordinate with the depletion of the intracellular levels of these polyamines following exposure at 43 degrees, extracellular levels of spermidine and spermine were increased. The ratio of intracellular to extracellular amounts of both these polyamines changed from 1 to 1.5 to approximately 0.2 to 0.3 after hyperthermic exposure. These cultures exposed to 43 degrees heat during G1 initially showed depressed levels of replicated DNA, but near-control rates of DNA replication were atained in a temporally related manner with the reaccumulation of intracellular spermidine and spermine levels. When cultures were exposed to 43 degrees heat in S phase, intracellular amounts of spermidine and spermine were again reduced and increased extracellular levels of these polyamines were observed. In these S-phase-treated cultures, cells were able to continue replicating their DNA but at a much reduced rate compared to controls. These results and other show that: (a) exposure of cells at 43 degrees causes a depletion of intracellular levels of spermidine and spermine, suggesting that an immediate aspect of thermal damage is a membrane defect that markedly affects the transport of these molecules across cell membranes; (b) exposure of either G1- or S-phase cultures to 43 degrees heat caused a depression of bulk DNA-synthetic rates resulting in a prolongation of S phase, and (c) the intracellular reaccumulation of spermidine and spermine following exposure of G1 cells to a 43 degrees heat shock is temporally related to the recovery of near-normal DNA synthetic rates in these cells.
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PMID:The relationship between polyamine accumulation and DNA replication in synchronized Chinese hamster ovary cells after heat shock. 83 72

Two endonuclease activities in rat liver for damaged DNA were assayed. Double-stranded, covalently closed DNA from phage PM2 was damaged by either ultraviolet irradiation or by heating at acid pH, and used as substrate for endonucleases specific for ultraviolet DNA damage and for DNA apurinic sites, respectively. The levels of both enzyme activities in livers of normal rats were compared to levels in livers of rats fed N-2-acetylaminofluorene. At critical stages of the carcinogenic regimen levels of both endonuclease activities were normal. This, together with other data, suggests that depression of excision-repair of DNA damage does not take place during experimental carcinogenesis.
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PMID:Normal endonuclease activities for damaged DNA during hepatocarcinogenesis. 88 9

Reserpine, a well-known CNS depressant which depletes central monoamine stores, was found to produce in the brains of 11-day-old rats a severe depression in cell proliferation in terms of the rate of [3H]thymidine incorporation into DNA. The effect was studied in detail 12 h after ther administration of the drug (2.5 mg/kg, s.c.) when the rate of in vivo DNA synthesis in the forebrain was about one-third of control: the decrease was less marked in the cerebellum (rate about two-thirds of control). It was possible to exclude side effects of the drug, such as restricted food intake, hypothermia and an elevation of the level of blood corticosteroids being responsible for the reduction of [3H]thymidine incorporation into DNA. Kinetic studies showed that reserpine had no marked effect on the entry of [3H]thymidine from blood to brain, but it caused some retardation in the rate of [3H]thymidine conversion into [3H]thymidine nucleotides. Nevertheless, the severe depression of DNA labelling was evident even after correcting the values on the basis of [3H]thymidine nucleotide concentrations. In contrast to these effects, thymidine kinase activity was normal in the brain of reserpine-treated animals.
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PMID:Effect of reserpine on cell proliferation in the developing rat bran: a biochemical study. 88 5

Exposure of dilute aqueous solutions of tryptophan to near UV light (320 to 390 nm) at subsolar levels yields fluorescent photoproducts capable of inhibiting the growth and differentiation of cultured mouse embryonic fibroblasts and fertilized sea urchin eggs. The ability of these cells to incorporate labelled precursors of protein, RNA, and DNA into their respective macromolecules was markedly inhibited by adding tryptophan preirradiated with near UV light to their incubation media. Thus the inhibition of growth and differentiation of these cells seems to result from a depression of their ability to synthesize macromolecules in the presence of the photoproducts.
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PMID:Inhibition of cell growth by near ultraviolet light photoproducts of tryptophan. 94 71

The principal psychoactive component of marihuana is delta-9-tetrahydrocannabinol. This compound at 10(-5) molar concentration in the medium of human cell cultures appeared to inhibit DNA, RNA, and protein synthesis by 50, 40, and 30% respectively, as measured by incorporation of radioactive precursors into acid-insoluble cell fractions in human diploid fibroblasts, human neuroblastoma cells, and mouse neuroblastoma cells. While delta-9-tetrahydrocannabinol inhibited semiconservative DNA synthesis, it had no effect on DNA repair synthesis in human cells as assayed by the photolysis of 5-bromodeoxyuridine incorporation into DNA during repair after ultraviolet radiation damage. Delta-9-tetrahydrocannabinol also had no effect on rejoining of DNA single-strand breaks induced by gamma-rays. The nonspecificity of the inhibition of macromolecular synthesis by delta-9-THC suggested a possible interference with uptake of radioactive precursors. However, experimentation has shown that this depression of macromolecular synthesis cannot be accounted for by reduced transport of radioactive precursors into the cell because the rate of transport of these precursors into the cell is essentially the same in the presence or absence of delta-9-THC. Pool sizes of macromolecular precursors as measured radioisotopically (3H-thymidine, 3H-uridine, 14C-leucine) appear to be reduced about 50%, and this reduced pool size could fully account for the reduced macromolecular synthesis seen in the presence of delta-9-THC. We do not know what causes this apparent reduction of pool sizes in the presence of delta-9-THC.
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PMID:delta-9-Tetrahydrocannabinol: effect on macromolecular synthesis in human and other mammalian cells. 94 11

Several reports have indicated the mutagenicity of the cycasin aglycone, methyl azoxymethanol (MAM). Van Den Berg and Ball (1972) have demonstrated the inhibitory effects of MAM acetate (MAMac), a more stable form of the aglycone, on DNA synthesis and cell proliferation in HeLa cells. The purpose of this study was to observe the effects of MAMac on blastogenesis in the human short-term leucocyte culture system. A depression in blastogenesis by MAMac was observed cytologically derived from two individuals. The same effect was observed utilizing [3H] thymidine as an indicator of blastogenesis in a series of cultures from 11 male individuals exposed to varying doses of MAMac, ranging from 5 through 800 mug/ml.
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PMID:PHA response and methylazoxymethanol acetate. 95 33

The proliferating cells of mouse epidermis (basal cells) can be separated from the non-proliferating cells (differentiating cells) Laerum, 1969) and brought into a monodisperse suspension. This makes it possible to determine the cell cycle distributions (e.g. the relative number of cells in the G1, S and (G1 + M) phases of the cell cycle) of the basal cell population by means of micro-flow fluorometry. To study the regenerative cell proliferation in epidermis in more detail, changes in cell cycle distributions were observed by means of micro-flow fluorometry during the first 48 hr following adhesive tape stripping. 3H-TdR uptake (LI and grain count distribution) and mitotic rate (colcemid method) were also observed. An initial accumulation of G2 cells was observed 2 hr after stripping, followed by a subsequent decrease to less than half the control level. This was followed by an increase of cells entering mitosis from an initial depression to a first peak between 5 and 9 hr which could be satisfactorily explained by the changes in the G2 pool. After an initial depression of the S phase parameters, three peaks with intervals of about 12 hr followed. The cells in these peaks could be followed as cohorts through the G2 phase and mitosis, indicating a partial synchrony of cell cycle passage, with a shortening of the mean generation time of basal cells from 83-3 hr to about 12 hr. The oscillations of the proportion of cells in G2 phase indicated a rapid passage through this cell cycle phase. The S phase duration was within the normal range but showed a moderate decrease and the G1 phase duration was decreased to a minimum. In rapidly proliferating epidermis there was a good correlation between change in the number of labelled cells and cells with S phase DNA content. This shows that micro-flow fluorometry is a rapid method for the study of cell kinetics in a perturbed cell system in vivo.
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PMID:Regenerative proliferation of mouse epidermal cells following adhesive tape stripping. Micro-flow fluorometry of isolated epidermal basal cells combined with 3H-TdR incorporation and a stathmokinetic method (colcemid). 100 May 70

The absence of pyrimidine dimer excision after UV irradiation in rat cell line was confirmed. The possibility of excision repair system depression by acidification of medium with H3PO4 in HeLa cells has been proved. The results obtained by two different methods of deproteinization and DNA isolation are in good conformity.
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PMID:Contribution to the study of excision repair following UV irradiation in mammalian cells cultivated in vitro. 100 59

Lactase deficiency, manifested clinically by lactose malabsorption, is often the only biochemical evidence of a residual disturbance of jejunal mucosal function after Escherichia coli enteropathy in the infant. Villous morphology is usually normal. A sustained depression of the processes of biochemical differentiation of lactase biosynthesis has been postulated to explain similar states of lactase deficiency, but a possible influence of altered epithelial cell turnover on the mucosal lactase levels has not been investigated. In ten infants with a residual lactose malabsorption, after E. coli infection, jejunal cell renewal activity and disaccharidase activities were studied by analysis of the exfoliated cells collected by lumenal perfusion. Significant increases in DNA and protein exfoliation and in the brush border activities of sucrase and lactase were observed during recovery from the malabsorptive disturbance. DNA and protein efflux increased almost linearly during a 20-day period. Lactase was initially four times more deficient than sucrase activity in the exfoliated cells. Both enzyme activities increased at almost identical rates. Therefore, it took longer for lactase activity to return to normal levels. The lactase/sucrase ratios approached normal at the end of the 20-day period. The changes in the exfoliating levels of the two enzymes, when analysed in relation to the increases in cell renewal activity, suggested a relationship between sucrase and lactase levels and cell age.
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PMID:Intestinal exfoliated cells in infant diarrhoea: changes in cell renewal and disaccharidase activities. 104 54

Cell suspensions of either mouse thymocytes or chick embryo cells were incubated with labelled precursors after preincubation with different cytostatic drugs. The total time of in vitro incubation was four hours. The ratio between the amount of incorporated labelled precursors and the total amount of DNA was determined and used to measure the cytostatic effect. All drugs used caused a marked depression of this ratio. The cytostatic drugs had no effect on the phosphorylation of thymidine.
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PMID:Effect of cytostatic drugs on nucleic acid synthesis in mouse thymocytes and chick embryo cells. 108 Apr 22


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