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E Ostergaard

Publications and source records attributed to E Ostergaard.

At least 37 records · Page 2Linked to original sources
PubMed1988

Stress-induced blocking of cell division in the colchicine arrest technique.

Previous studies have shown that procedures commonly used in studies of cell population kinetics in laboratory animals cause a transient block of the entrance of cells into mitosis. The purpose of the present study was, therefore, to examine whether the handling of animals in conjunction with the administration of colchicine affects the results obtained by the metaphase arrest technique. Groups of rats were injected with colchicine or saline at 1300 h and sacrificed at regular intervals during the following 140 min. Histological sections of the palatal mucosa were produced and the number of metaphases was assessed in the epithelium. In both the saline-treated and colchicine-treated groups the numbers of metaphases decreased immediately after injection and reached a minimum within 30 min. After that time a transient increase was observed in the saline group, whereas the number of metaphases in the colchicine-treated group increased continuously during the experimental period. These results indicate that colchicine takes effect after a delay period of 30 min and that the handling procedures in conjunction with the administration of colchicine provoke a transient block of the entry of cells into mitosis. The second part of the study was designed in such a way that the number of metaphases collected during a 2 h period under the influence of stress induced by injection of colchicine could be compared with the number of metaphases collected during the same time period without the influence of stress.(ABSTRACT TRUNCATED AT 250 WORDS)

Albinism↗
PubMed1987

Purification and characterization of an inducible mitochondrial DNA polymerase from Tetrahymena thermophila.

Treatment of the eukaryotic organism Tetrahymena with various types of DNA-damaging agents has been reported to cause a 35-fold induction of a mitochondrial DNA polymerase. We here report that the enzyme can be induced in large-scale cultures by exposure of the cells to thymine starvation and/or intercalating agents. The induced DNA polymerase has been purified to near homogeneity, with a specific activity of approx. 300,000 units/mg protein. The relative molecular mass of the active form of the enzyme is approx. 100,000, as determined by glycerol gradient sedimentation. The subunit structure has been analysed by SDS polyacrylamide gel electrophoresis of the highly purified preparation and by immunoprecipitation with a monoclonal antibody directed to the DNA polymerase. A polypeptide of Mr 47,000 has been observed to be a subunit of the enzyme. This corresponds to the size of the subunits suggested for mitochondrial DNA polymerase from chicken embryos and mouse myeloma cells.

DNA-Directed DNA Polymerase↗
PubMed1987

The effect of prolonged stress-inducing electrical stimulation on cell proliferation in rat palatal epithelium.

This study examines whether blocking of cell division by stress-inducing electrical stimulation can be maintained for a prolonged period of time and whether this results in the accumulation of a large number of cells ready to divide when the block is released. A total of 96 rats was subjected to electrical stimulation at intervals of 30 min for periods of 2, 4, 6 or 12 hr. Groups of animals were killed every second hour during these stimulation periods. After 2, 4 and 6 hr groups of animals were exempted from further stimulation and killed 2 or 4 hr later. After termination of the 12 hr stimulation period, groups of animals were killed every second hour during the succeeding 24 hr. Forty-eight animals were left undisturbed and served as controls. Two and a half hours prior to death, each of the experimental and control animals was injected intraperitoneally (i.p.) with colchicine. Histological sections of the palatal mucosa were prepared and the numbers of arrested metaphases were counted. The electrical stimulation for 2, 4, 6 and 12 hr consistently resulted in a reduced number of cells entering mitosis, indicating a blockade at the G2/M transition. However, with an increase in the length of electrical stimulation, an increasing number of cells passed the block, while a decreasing number entered mitosis during the first 4 hr following cessation of the stimulation. The sum of metaphases accumulated during the various stress periods and the following 4 hr was always similar and consistently lower than the number of metaphases accumulated in the control animals within the same time periods. This observation indicates that, during stress-inducing electrical stimulation and the succeeding 4 hr, only a defined number of cells can enter the mitotic phase. Thus, in addition to the block at the G2/M transition, there appears to be another block of cell division at an earlier stage in the cell cycle.

Animals↗
PubMed1986

Pharmacokinetics of erythrocyte methotrexate in children with acute lymphoblastic leukemia during maintenance treatment.

The concentration of methotrexate (MTX) in erythrocytes (E-MTX) was measured in 47 children with acute lymphoblastic leukemia during maintenance treatment with MTX 1.7-21.6 mg/m2/week and 6-mercaptopurine 25-75 mg/m2/day. At the time of measurement the plasma MTX concentration was less than 2 nmol/l. The steady state E-MTX varied between 51 and 202 nmol/l erythrocytes. Alterations in the E-MTX took place over 8-12 weeks after a change in dosage. A significant correlation was found between the E-MTX and the weekly dose of MTX administered. Noncompliance was revealed in two patients. A very low E-MTX was found in one patients, probably caused by inhibition of erythropoiesis. No correlation was found between E-MTX and the total amount of MTX administered or the length of treatment. A terminal half-life of 2-5 weeks after discontinuation of the drug showed that the erythrocytes functioned as a slow-changing compartment for MTX. Unexpectedly low E-MTX could mean noncompliance, impaired erythropoiesis, altered metabolism, or poor drug absorption.

Absorption↗
PubMed1983

Blocking of the cell division by stress-inducing electrical stimulation. A study in rat oral epithelium.

The purpose of the present study was to localize in the cell cycle, the site of the stress-induced blockage of cells entering the mitotic phase, and to estimate the length of time this block is effective. A total of 140 rats were subjected to electrical stimulation applied by a live metal grill in the bottom of their cages. Forty animals left undisturbed in the cages were used as controls. At various intervals after the start of electrical stimulation, groups of animals were killed and histologic sections were prepared of the palatal mucosa. The number of prophases, metaphases, and ana/telophases was counted in the epithelium in three sections of each animal. Electrical stimulation for 1 min resulted in a blocking of the entrance of cells into mitosis, followed by a transient increase in the number of mitotic figures to a level much higher than that of the controls. Electrical stimulation for 10 min resulted in the maintenance of the blocking effect for approximately 45 min. By renewed electrical stimulation the period of blockage was extended for a further 35 min. In each experiment the number of prophases decreased immediately after the start of electrical stimulation, indicating that the site of the blockage of the entrance of cells into mitosis is located near the G2/M transition.

Anaphase↗
PubMed1982

The effect of environmental stress stimuli on cell division in rat palatal epithelium.

The effect on cell proliferation of procedures commonly used in studies in laboratory animals was examined in the palatal epithelium of rats. Groups of rats were exposed to ether anaesthesia, immobilization in the supine position or to cage change. Animals left undisturbed in the cages during the experiment were used as controls. At intervals of 30 min, four animals of each group were killed and histological sections of the palatal mucosa were prepared. The number of prophases, metaphases and ana/telophases in the epithelium was counted and related to 1 mm2 of the surface. Thirty minutes after the various procedures the number of metaphases and ana/telophases were extremely low. After a further 30 min a high number of prophases was observed. The number of metaphases rose within the following 30 min, during which time the number of ana/telophases also reached a maximum. These observations indicate that the environmental stimuli have blocked the entrance of cells into mitosis and have resulted in an accumulation of cells, which, following the raising of the blockade, pass through the various stages of the mitotic phase. In studies of cell population kinetics the blockade of cell division as a result of environmental stress stimuli may lead to misleading results.

Animals↗