bluuebunny/crossref_metadata_2025_split huggingface dataset:
Time‐dependent effects of removal of the pars distalis of the pituitary gland on toad epidermal cell and tissue kinetic parameters
Authors: Budtz Povl E. 
Published: May 2008

Abstract. Amphibian moulting and its hormonal control has been extensively studied, but the possible influence of hormones on epidermal proliferation has been less investigated. In the present contribution to studies on the control of epidermal homeostasis, the proliferative pattern of the toad epidermis following ablation of the pars distalis of the pituitary gland is analysed by an investigation of the changes in the epidermal cell number, metaphase index and [3H]thymidine incorporation at various times after the operation.During the first 24 hr after pars distalis ablation, labelling index (LI) increased concurrently with an initial decrease in the metaphase index (MI), followed by an increase. During the same period of time the mean grain count (MGC) and the grain distribution pattern also changed. From 24 hr to 7 days after operation, MI, LI, and MGC were significantly lower than those of controls, but increased to control levels at 14 days after the operation. Phase durations and their possible changes were not measured directly, but data showed that the S‐phase duration (Ts) and the mitotic duration (TM) must have changed in relation to each other during the experiment. Assuming that the MGC is a rough estimate of the DNA‐synthesis rate, the compatibility of a postulated change in phase duration with the observed MGC was analysed. This analysis revealed that TS and TM could have decreased up to 18 hr after the operation, whereas these phase durations, after 24 hr and during the rest of the experiment, increased compared to those of controls. Even with these possible changes in phase durations, and in the absence of direct assessment of cell division rates, the observed cell kinetic parameters appeared incompatible with an increased rate of proliferation. This was surprising since the efflux of cells from the living, subcorneal epidermis to the stratum corneum was significantly increased after pars distalis ablation, without a concurrent decrease in the stratum corneum recruitment cell pool (SCRP‐number of subcorneal epidermal cells per mm surface). Possible reasons for the discrepancy between the expected increase in proliferation following pars distalis ablation, and the failure to demonstrate this, are discussed.
A Comparison of Low and High Dose‐Rate Radiation For Recipient Mice In Spleen‐Colony Studies
Authors: Lord B. I. , Hendry J. H. , Keene J. P. , Hodgson B. W. , Xu C. X. , Rezvani M. , Jordan T. J. 
Published: May 2008

AbstractOver the last 15 years, endogenous spleen‐colony formation in our mice, following lethal irradiation, has increased to an unacceptable level. It has been found necessary, therefore, to introduce a new method of preparing recipient mice for spleen‐colony studies. Irradiation with low dose‐rate 60Cobalt γ rays has been compared with high dose‐rate linear accelerator electrons, and their effects on endogenous spleen colony formation compared with earlier X and γ ray dose‐response data. It was found that a large dose (13.5 Gy) of γ rays results in fewer endogenous colonies than 8.5 Gy of electrons, yet because of its low dose rate (14.1 × 10−3 Gy/min) it has a marked sparing of the intestinal tissue as measured by the intestinal microcolony technique. This in turn permits better survival and, therefore, a ‘healthier’ animal for spleen‐colony work. Exogenous colony formation is also lower in the low dose‐rate, γ‐irradiated recipients and this is shown to be due to a reduced spleen‐seeding efficiency.It is concluded that very low dose‐rate radiation is preferable for haemopoietic ablation, that a mouse colony requires constant monitoring for changes of endogenous spleen‐colony formation and that the spleen‐seeding efficiency of CFU‐s depends on the irradiation technique used‐there is no absolute value for a given strain of mouse.
Delay In Entry Into S Phase After Heat Shock
Authors: Dewey D. L. , Holden J. L. 
Published: May 2008

AbstractSynchronized cells of the Harding Passey melanoma grown in culture were given a heat shock treatment of 44° C for 36 min. Thymidine incorporation was measured at frequent intervals after heat shock to determine the time of onset of the next DNA synthetic period.If the heat shock was given at the end of G1, the following S was delayed by 20 hr. Heating at other times in the cell cycle resulted in an even longer interval before the onset of S. the end of G1 was also the most resistant to hyperthermic killing and to the effect of heat on the magnitude of thymidine incorporation in the following S. Heating the cells a second time did not repeat the effect of the first treatment unless the second heat shock treatment was at a considerably higher temperature. Thus thermotolerance to heat shock killing also applies to cell‐cycle delay.
Decrease in the ability of CFU‐s in shielded marrow to be recruited into cell cycle after multiple irradiations: experimental results and computer simulations
Authors: Sainteny F. , Guiget M. , Mary J. Y. 
Published: May 2008

AbstractNine doses of 1.5 Gy given to mice with one shielded leg result in very similar perturbations in shielded marrow (CFU‐s kinetics whatever the source of radiation (X or γ rays). At the time of the ninth irradiation, the size of the shielded CFU‐s compartment is reduced to 75% of control level. After 15 min it decreases to 47% and, 1 day later, remains below the pre‐ninth irradiation level (62% of control level) in spite of two significant peaks of CFU‐s in DNA synthesis, at 1 and 8 hr after the ninth irradiation. For acceptable fitting to experimental data, computer simulations make it necessary to assume that a fraction of shielded marrow CFU‐s is not capable of entering the cell cycle after the treatment. This is not explainable by defects in the stimulators of CFU‐s proliferation secreted by shielded haemopoietic tissue because their production and their efficacy are demonstrated to be normal after the nine exposures. the incomplete recovery of the shielded CFU‐s pool from porliferating CFU‐s can be attributed to a loss in CFU‐s by differentiation at birth.
Proliferation Kinetics of A Human Malignant Melanoma Serially Grown In Nude Mice
Authors: Spang‐Thomsen M. , VindelØv Lars L. 
Published: May 2008

AbstractThe technique of labelled mitoses and flow cytometric DNA analysis were used to determine the proliferation kinetics of a human malignant melanoma grown in nude mice. the effect of tumour volume and of long‐term serial transplantation on the kinetic parameters was investigated.The results showed that the cell loss factor, which was the dominant factor in the growth of this melanoma, increased from 52 to 69% with increasing tumour size, whereas the calculated growth fraction showed no systematic changes. the cell generation time increased from 34 to 44 hr with tumour size, mainly due to a prolongation of the G1, duration time, whereas no significant changes occurred in the duration of the S and G2, phases of the cell cycle. the stability of the investigated tumour characteristics indicated that the kinetics of this melanoma remained unchanged during more than sixty serial transplantations in nude mice. the methods applied are suitable for a detailed description of tumour growth kinetics, since they provide complementary results.
Comparative Investigations On the Effect of Different Dose Schedules of the Phase‐Specific Drug Vincristine (Vcr) On the Proliferation Kinetics of A Solid Experimental Tumour
Authors: de Lacroix W. Féaux , Mallmann H. 
Published: May 2008

AbstractThe aim of the present investigation was to study the effect of a high bolus injection (1 × 2.1 mg) of vincristine (VCR) during the phase of tumour growth retardation at the 14th day after transplantation and to compare the findings with the results of single (1 × 0.35 mg) and repeated (6 × 0.35 mg) applications of this cytostatic drug. Furthermore, an attempt was made to induce a synchronization of tumour cell proliferation. It was found that the effect on the volume growth was very pronounced after the high bolus injection and the repeated application of vincristine compared with the single low dose of the cytostatic drug. A synchronization of the tumour cell proliferation by flow out of the mitotic block could not be demonstrated. On the other hand a modest simultaneous recruitment of previously non‐cycling tumour cells into the cell cycle occurred in the periphery of the tumour after the high bolus injection. the repeated application and the high bolus injection of VCR increased the cytostatic effect, especially in the tumour centre, related to the more slowly proliferating tumour cell compartment.
Pattern of Dna Synthesis and Its Effect On the Classification of Cells By Flow Cytometry
Authors: Culpin D. , Morris V. B. 
Published: May 2008

AbstractA flow cytometer produces a DNA distribution which contains information about the proportions of cells in various phases of the cell cycle. In this report we show that the form assumed for the rate of DNA synthesis in a cell plays an important part in the estimation of those proportions. We compare three forms for the rate of DNA synthesis, one of which is derived from knowledge of the mechanism of DNA replication, and find that they give substantially different estimates of the proportions of cells in the G1 and G2+ M phases.
Clonal Attenuation In Chick Embryo Fibroblasts Experimental Data, A Model and Computer Simulations
Authors: Angello J. C. , Prothero J. W. 
Published: May 2008

AbstractWhen cells from mass cultures of chick embryo fibroblasts are grown at very low density, some cells yield large clones while others produce smaller clones, and some cells fail to divide at all. the distribution of clone sizes is related to the number of population doublings which the donor mass culture has undergone: the more doublings which have occurred, the smaller the average clone size. In this report we describe a model which analyses this phenomenon, referred to as ‘clonal attenuation’, in detail.The model is based on the concept that a cell with hypothetically unlimited replicative potential—i.e. a ‘stem’ cell—can become ‘committed’ to a programme of limited replicative potential. This event is assumed to be stochastic and to have a fixed probability per stem cell division. the parameters of the model are: Pc, the probability of commitment; N, the number of differentiative divisions; and Tc, the cell‐cycle times. By computer simulation, it is shown that Pc increases roughly exponentially at each successive stem cell division. According to the model, when the daughter of a stem cell becomes committed, its progeny proceed through N obligatory divisions before becoming terminally differentiated (post‐mitotic). the best‐fit value of N was found to be seven.The simulations also reveal that the absolute number of stem cells in the total population increases for most of the lifespan of the culture. When Pc becomes much greater than 0.5, the number of stem cells declines rapidly to zero, and the culture nears senescence.Sensitivity analysis shows that Pc can assume only a limited range of values at each stem‐cell division.
Kinetics of Micronucleus Expression In Synchronized Irradiated Chinese Hamster Ovary Cells
Authors: Brock William A. , Williams Marcia 
Published: May 2008

AbstractThe kinetics of expression of radiation‐induced micronuclei (MN) in synchronized Chinese hamster cells (CHO) was examined. the purpose of the study was to determine if the cell cycle distribution of a population significantly influences the levels of radiation induced MN, thereby obscuring the exact quantification of the radiation effect. Cells were synchronized by centrifugal elutriation, irradiated, and then different phases of the cell cycle were examined for: cell cycle progression, division probability, and temporal expression of MN. the results demonstrate that the time interval for maximal MN expression is long enough that the position of cells in the cell cycle and radiation induced division delays do not prevent the majority of cells from completing their first post‐irradiation mitosis, therefore, expressing MN. By following the progression of synchronized cell populations by flow cytometry and also examining the time of division of individual cells for 24 hr after irradiation, we observed that the maximum number of cells from all phases of the cell cycle are in their first post‐irradiation interphase at that time, thus explaining the MN results.
A Novel Approach to the Study of Kinetically Changing Cell Populations
Authors: Sheridan J. W. 
Published: May 2008

AbstractA method is described for estimating changes in cell cycle times during periods of rapid change in proliferation rate. This method, which depends upon the interpretation of pre‐ and post‐velocity sedimentation fractionation continuous thymidine labelling patterns, exploits the relationship between sedimentation rate and cell cycle location. By this means, cycle times can be estimated under conditions that are difficult (if not impossible) to analyse by FLM methods.
Epidermal Tissue Homeostasis
Authors: Budtz Povl E. 
Published: May 2008

Abstract. Following removal of the pars distalis of the pituitary gland in toads, epidermal efflux from the stratum corneum recruitment cell pool (i.e. production of corneal layers) is greatly increased. In this investigation the cell birth rate is studied by means of the metaphase arrest technique, as a function of time after pars distalis ablation. the method allows assessment of the total cell production over 14 days after the operation, to be compared with the total efflux and changes in the epidermal cell pool size.Whereas in intact toads the rate of cell production exceeds that of cell loss by moulting by a factor of 2.7, the ‘surplus’ of cells neither being used for formation of corneal layers nor permanently accommodated within the living epidermis, a ‘balance sheet’ of efflux and influx indicates that following pars distalis ablation all cells produced are also used for the (excessive) formation of corneal cell layers.The observations lend further support to the hypothesis that controlled cell deletion is a tissue homeostatic mechanism complementary to controlled cell divisions.
Effects of Hydroxyurea On the Mitotic Activity and the G2 Phase In Hairless Mouse Epidermis
Authors: Iversen Olav Hilmar , Harket Gunvald , Rabe Ragnar 
Published: May 2008

AbstractHairless mice were given 5 mg hydroxyurea (HU) intraperitoneally (i.p.) followed by 0.15 mg Colcemid® at various times after HU. the animals were killed at 2 and 4 hr after Colcemid, the epidermal mitotic counts in dorsal skin were determined and the mitotic rates calculated. These were compared with the normal mitotic rates, and the ratios between the results from HU‐treated and ‐untreated animals were calculated. Hydroxyurea caused a considerable reduction in the mitotic rate with a trough at 6 hr, followed by a wave of increased mitotic rate with a peak at 14 hr, followed by a secondary drop at 20 hr, and then a return to normal.Another group of mice were given HU only, and the fraction of epidermal cells in G2 was measured by flow cytometry. From these animals, without previous injection of Colcemid, we also determined the mitotic counts and calculated the mitotic durations. Cells piled up in G2 for the first 6 hr after HU injection, then the G2 compartment was emptied. the results are discussed in relation to previous results from this department showing the effect of the same dose of HU on DNA synthesis in the same mouse strain. It is concluded that HU not only blocks or retards DNA synthesis in epidermal cells, but also affects the movement of cells through G2 and M. the cell kinetic effects of HU thus seem to be very complex.
Proliferation of Cardiomyocytes and Interstitial Cells In the Cardiac Muscle of the Mouse During Pre‐ and Postnatal Development
Authors: Cluzeaut Françoise , Maurer‐Schultze Brigitte 
Published: May 2008

AbstractProliferation of cardiomyocytes and interstitial cells in the cardiac ventricle of the mouse during pre‐ and postnatal development was studied. Furthermore, the number of cardiomyocyte and interstitial cell nuclei per unit area was determined on histological sections.The labelling index of cardiomyocytes decreases from 23% on day 14 of gestation to about zero at 3 weeks after birth. the number of cardiomyocyte nuclei per unit area increases up to day 16 of gestation and then continuously declines. This coincides with the concept that the increase in size of the heart during early fetal life is mainly due to hyperplasia, while during late fetal life and after birth it is mainly, and during adult life exclusively, due to hypertrophy of cardiomyocytes. Proliferation of interstitial cells continues up to 5 days after birth and then decreases. the ratio of cardiomyocytes to interstitial cells decreases by a factor of about 10 between day 14 of gestation and 3 weeks after birth.
A Modified Harlequin Stain For Cell Kinetics
Authors: Pincu Madeleine , Kimme‐Smith Carolyn , Norman A. 
Published: May 2008

AbstractLymphocytes cultured with 4 × 10‐4 m bromodeoxyuridine (BrdU) and stained by the harlequin procedure show wide variations in the colour and texture of their interphase nuclei. We demonstrate that we are able, by inspection, to identify four sets of nuclei: small dark nuclei (D) in cells that have not transformed in response to mitogenic stimulation; red nuclei (R) in transformed cells that have not synthesized DNA in culture; speckled nuclei (S)—red speckles on a bluish background—in cells that are synthesizing DNA for the first time in culture; blue nuclei (B) in cells that have completed one or more cycles of DNA synthesis. By using this modified harlequin stain to score the fraction of proliferating cells, and using the modified or conventional harlequin stain to determine the relative frequencies of mitotic cells in the first, second, or later divisions, we are able to estimate the fraction of lymphocytes in the original blood sample that can divide in culture. In addition, we show that the technique lends itself to automation. For this we have digitized black and white video images of the cells and extracted features based on the distribution of optical densities in the nuclei. Discriminant analysis carried out on these descriptors resulted in the correct classification of the three major groups R, S and B with an accuracy of 80.3%, 58.5% and 85.1%, respectively.
Synchronization of the Human Promyelocytic Cell Line HL 60 By Thymidine
Authors: Mortensen Børge T. , Hartmann Niels R. , Christensen Ib J. , Larsen Jørgen K. , Kristensen Tom , Wieslander Steen B. , Nissen Nis I. 
Published: May 2008

AbstractCultures of the promyelocytic cell line HL 60 were synchronized with thymidine. A concentration of 0.05 mM thymidine and an exposure time of 24 hr was found optimal for blocking about 90% of the cells in S phase. Following release from the thymidine block the cell cultures were followed intermittently over 40 hr for fluctuation in cell numbers, labelling with radioactive thymidine and nuclear DNA distributions.Mathematical evaluation of the results revealed a cycling time of 18.6 hr and a duration of specific cell phases of 8.6 hr, 7.1 hr and 2.9 hr for G1, S and G2+ M, respectively. the doubling time was 26 hr and the growth fraction was estimated as 1.
Effect of diabetes on the rhythm of r[3H]thymidine incorporation in Con‐A‐stimulated mice splenocytes
Authors: Prunet J. , Panijel J. 
Published: May 2008

Abstract. The chronogram of hyperglycaemia in alloxan‐induced diabetic DBA/2 mice (living under conditions standardized for light‐synchronized periodicity and fed ad libitum) presented an ultradian rhythm (during spring) different from the circadian blood glucose chronogram of normal control mice.Simultaneously, the [3H]hymidine ([3H]TdR) incorporation chronogram of diabetic mouse splenocytes, stimulated or unstimulated with Concanavalin‐A (Con‐A), was changed and unbalanced, compared to that of normal control mice.Previous experiments showed that the [3H]TdR incorporation chronogram of stimulated or non‐stimulated splenocytes of normal DBA/2 mice presented seasonal variations. They were characterized generally by an ultradian rhythm. Yet, during spring, they exhibited a circadian rhythm because one phase was advanced and superimposed on the other, the latter being typically unvarying.It seems probable that the unbalanced rhythm of [3H]TdR incorporated in diabetic mouse splenocytes, stimulated or not, was responsible for a dysfunction of that population in diabetes.
Evidence For Cell Generation Controlled Proliferation In the Small Intestinal Crypt
Authors: Meinzer H. P. , Sandblad B. 
Published: May 2008

Abstract. In this paper we discuss the hypothesis that cell proliferation is controlled by the number of generations after leaving an ‘eternal’ stem cell. the theory is based on a simulation of the kinetic behaviour of cells in the intestinal crypts. There is evidence of three, four and five generations of cells which are allowed to enter mitosis in the lower and upper part of the normal intestinal tract, and in some disease states, respectively. We suggest an internal proliferation control: some kind of knowledge that cells carry from generation to generation. It is an open question what sets and changes the generation counter: internal genetic information or external influences such as growth factors or chalones.The geometric shape of the epithelial tissue in the intestinal tract can be understood as the steady state of a highly dynamic process. Age and death are determined from the beginning; cell‐cell interaction or communication is not necessary and can be neglected. Our theory will be illustrated using the intestinal crypts as they are easily accessible, of a simple structure and completely described in the literature.
Role of splenic stroma in the action of bacterial lipopolysaccharides on radiation mortality: a study in mice carrying the Slj allele
Authors: Ploemacher R. E. , Brons N. H. C. 
Published: May 2008

Abstract. Slj/+ mice display a slight macrocytic anaemia due to a defect in their haemopoietic organ stroma. They have a deficient endogenous spleen colony (CFU‐end) formation following sublethal doses of gamma‐radiation compared with their normal +/+ littermates, which is likely to be due to the low pre‐irradiation CFU‐S content of the Slj/+ spleen. CFU‐S in these congenic mice do not differ in their sensitivity to gamma‐irradiation or stem cell‐activating factor.While injection of +/+ mice with 10 μg of lipopolysaccharide‐W (LPS) one day prior to irradiation led to a substantial increase in their survival, the survival of Slj/+ mice was only slightly increased. Irradiation induced a similar dose‐related reduction in the numbers of CFU‐S in the spleen and femora of LPS‐injected Slj/+ mice compared to similarly treated +/+ mice when measured directly after irradiation. At Day 9 after irradiation, injection of LPS led to a significantly higher CFU‐end formation and higher numbers of CFU‐S and nucleated cells in the Slj/+ spleens compared to LPS‐injected +/+ mice. No such differences in the radioprotective effect of LPS were observed in the +/+ and Slj/+ mice with respect to the splenic and femoral 59Fe‐incorporation and the femoral CFU‐S numbers at Day 9.These data strongly suggest a contribution by immigrating CFU‐S to the CFU‐S numbers and endogenous colony formation in at least the Slj/+ spleen after LPS injection and subsequent sublethal irradiation. The observations also imply that the splenic organ stroma may play a mediatory role in the radioprotective action of LPS. In addition, the data represent an extreme example of a lack of correlation between animal survival and haemopoietic parameters. Caution should be taken when applying endogenous colony counts as a means of screening potential anti‐radiation drugs.