bluuebunny/crossref_metadata_2025 huggingface dataset:
CHARACTERISTICS OF THE ISOPRENALINE STIMULATED PROLIFERATIVE RESPONSE OF RAT SUBMAXILLARY GLAND
Authors: Koschel K. W. , Hodgson G. S. , Radley J. M.
Published: May 2008

A simple stochastic model has been developed to determine the cell cycle kinetics of the isoprenaline stimulated proliferative response in rat acinar cells. The response was measured experimentally, using 3H‐TdR labelling of interphase cells and cumulative collections of mitotic cells with vincristine. The rise and fall of the fraction of labelled interphase cells and of metaphase cells is expressed by the product of the proliferative fraction and a difference of probability distributions. The probability statements of the model were formulated and then compared by an iterative fitting procedure to experimental data to obtain estimates of the model parameters. The model when fitted to the combined fraction labelled interphase (FLIW) and fraction metaphase (FMW,) waves gave a mean Gis transit time of 21‐2 hr, mean Gis+ S transit time of 270 hr, and mean Gis+ S + G2 transit time of 35‐8 hr for a single injection of isoprenaline, where Gis is the initiation to S phase time. When successive injections of isoprenaline were given at intervals of 24 and 28 hr the corresponding values after the third injection were 12‐4 hr, 20‐8 hr and 25‐7 hr respectively. The variance of the Gis phase dropped from 18‐1 to 1–3 while the other variances remained unchanged. The estimated proliferative fraction was 0–24 after a single injection of isoprenaline, and 0–31 after three injections of the drug. Independently determined values of the proliferative fraction, obtained from repeated 3H‐TdR injections, were 0–21 and 0–36 respectively.
STUDY ON THE PROLIFERATIVE STATE OF HAEMOPOIETIC STEM CELLS (CFU)
Authors: NEČAS E. , POŇKA P. , NEUWIRT J.
Published: May 2008

Hydroxyurea was used to study the proliferation rate of haemopoietic stem cells (CFUJ in normal mice, after irradiation or transplantation into irradiated recipients. It was demonstrated that the proliferation rate of endogenous CFUS (endo‐CFU,) and exogenous CFUS (exo‐CFUs) are identical. After irradiation (650 R) the surviving endo‐CFUs begin to proliferate immediately. By contrast exo‐CFU, transplanted into the irradiated recipient mouse (850 R), begin to proliferate only after about 30 hr.

However, injection of isoproterenol (which stimulates adenyl cyclase) or dibutyryl cyclic adenosine 3′,5′‐monophosphate shortly after marrow cell graft, triggers the transplanted CFUS into cell cycle as shown by an almost immediately increased sensitivity to hydroxyurea. Isoproterenol is capable of inducing DNA synthesis also in stem cells of normal mice but it takes about 20 hr before CFU, become to be increasingly sensitive to hydroxyurea.
THE MIGRATION OF LYMPHOCYTES ACROSS SPECIALIZED VASCULAR ENDOTHELIUM
Authors: Sedgley M. , Ford W. L.
Published: May 2008

The chain of lymph‐nodes in the rat mesentery was isolated and the preparation was perfused via cannulae in the superior mesenteric vessels. The perfusate consisted of serum to which labelled lymphocytes had usually been added. The entry of radioactively labelled lymphocytes from the blood vessels into the lymph‐nodes was studied by scintillation counting and autoradiography.

It was observed that: (1) In the perfused node labelled lymphocytes localized in and around post‐capillary venules in the paracortex as they do early after i.v. injection. (2) The number of lymphocytes which entered the node was directly proportional to the concentration in the perfusate over the range studied. The proportion of cells retained in the node varied considerably around a mean of 11 % of lymphocytes reaching it. (3) The isolated lymph‐node released few if any lymphocytes into the effluent (venous) perfusate. (4) Large lymphocytes migrated into isolated lymph‐nodes slightly more readily than did small lymphocytes. (5) Unlike intact cells isolated lymphocyte membranes did not adhere to specialized vascular endothelium.
A TWO EMULSION AUTORADIOGRAPHIC TECHNIQUE AND THE DISCRIMINATION OF THE THREE DIFFERENT TYPES OF LABELLING AFTER DOUBLE LABELLING WITH 3H‐ AND WC‐THYMIDINE
Authors: Schultze B. , Maurer W. , Hagenbusch H.
Published: May 2008

The first part of the paper deals with a two emulsion autoradiographic technique for double labelling experiments with 3H‐ and 14C‐thymidine which permits a clear discrimination of the different types of labelling.

In the second part the application of this technique to cell kinetic studies is discussed. Accurate discrimination between the different types of labelling, namely purely 3H‐, purely 14C‐ and double (3H +14C) labelling, is only possible if the activity ratio of 3H‐ to 14C‐thymidine is sufficiently high. This condition is necessary for a reliable distinction between those grains in the first emulsion which are due to true 3H‐labelling and spurious grains which are simultaneously produced in the same emulsion by 14C‐β‐particles. Experiments are described to determine the required activity ratio of 3H‐ to 14C‐thymidine.
ALTERATIONS IN 3H‐THYMIDINE INCORPORATION INTO DNA INDUCED BY METHYL CCNU [1‐(2‐CHLOROETHYL)‐3‐(4‐METHYL CYCLOHEXYL)‐1‐NITROSOUREA] IN NORMAL AND TUMOROUS TISSUES IN VIVO
Authors: Young Robert C. , Goldberg Diana , Grotzinger Karen R.
Published: May 2008

Methyl CCNU produces a suppression of tritiated thymidine (3H‐TdR) incorporation into DNA in vivo in normal bone marrow and gastrointestinal tissues which is different in magnitude and duration from that seen in L1210 ascites tumor in the same animals. This suppression and recovery pattern is not seen in animals bearing L1210 ascites tumor resistant to MeCCNU. Where a different pattern of recovery is seen between normal host target tissues and tumor, the pattern can be exploited to increase the cure rate of animals bearing advanced L1210 ascites tumor with properly spaced second doses of MeCCNU. Additional information on the potential toxicity of second doses of MeCCNU can be predicted from knowledge of the time of recovery of DNA synthesis in the normal host target tissues.
PROPERTIES OF G0 CELLS: VARIATIONS IN THE PROLIFERATIVE RESPONSE FOLLOWING ISOPRENALINE
Authors: Radley J. M. , Hodgson G. S. , Koschel K. W.
Published: May 2008

The proliferative behaviour induced in the acinar cells of the rat submaxillary gland in response to isoprenaline has been used to examine the transit time of cells from a quiescent (G0) state into the S phase. Cumulative 3H‐TdR labelling index curves were constructed to determine the mean time interval (Gis time) between stimulation with isoprenaline and entry into the S phase. Data were collected for the proliferative wave induced by three sequential injections of isoprenaline, and the effects of varying the interval between the second and third injections of isoprenaline, and of changing the dose of the drug, were examined. Intervals of 28, 52 and 76 hr between isoprenaline injections resulted in mean Gis times of 16‐2, 20‐9 and 25‐6 hr respectively. It was concluded that the Gis time depended on the recent history of cells with respect to stimulation, but not division. The results are considered in terms of two models, in one of which the time to leave G0 is variable, whilst in the other the cells leave G0 immediately the stimulus is applied.
EXTRACELLULAR STIMULATION OF EPIDERMAL DNA SYNTHESIS
Authors: ROTHBERG S. , Nancarrow Grace E. , Meydrech E. F. , Iwanik M. J.
Published: May 2008

The removal of the topmost cell layers of the epidermal stratum corneum by stripping initiates a series of biochemical events which alters the normal homeostatic control of and results in the acceleration of the cell cycle in basal cells which are ten to twenty cell layers removed from the site of stripping. One measure of accelerated events is a stimulation of thymidine incorporation into epidermal DNA at time intervals following stripping. Two peaks of maximal stimulation occur between 12 and 24 hr and 48 and 54 hr after stripping.

Stimulation of thymidine incorporation into epidermal DNA by limited stripping is a useful technique for studying the stripping‐initiated signal at the stratum corneum and its subsequent translation at the proliferative cell receptor site.
CELL‐CYCLE ANALYSIS OF PERTURBED CELL POPULATIONS: COMPUTER SIMULATION OF SEQUENTIAL DNA DISTRIBUTIONS
Authors: Gray Joe W.
Published: May 2008

A mathematical model is presented that permits simulation of a time sequence of DNA distributions with a single set of cell‐cycle parameters. The method is particularly suited to the quantitative analysis of sets of sequential DNA distributions from perturbed cell populations. The model permits determination of the durations and associated dispersions of the phases of the cell cycle as well as the point in the cell cycle at which the perturbing agent exerts its effect. The mathematical details of the simulation technique are presented, and the technique is applied to the analysis of DNA distributions from perturbed cell populations. Three cell populations are modeled: CHO‐line cells released from a block at the interface of the G1 and S‐phases, 3T3 cells released from a G1‐phase block produced by serum starvation, and S49 mouse lymphoma cells responding to a block in the G1‐phase produced by N6,02′‐dibutyryl adenosine 3′:5′‐cyclic monophosphate (Bt2cAMP).
PERTURBED CELL PROLIFERATION KINETICS OF THE EMT6/M/AC TUMOUR IN MICE TREATED WITH ANTI‐MOUSE LYMPHOCYTE SERUM
Authors: Watson James V.
Published: May 2008

The cell proliferation kinetics of the EMT6/M/AC tumour were determined at two volumes, 6‐3 mm3 and 180 mm3, in mice treated with anti‐mouse lymphocyte serum, AMLS. Comparison of the growth curve with that obtained in non‐AMLS treated animals showed a marked increase in the growth rate at all volumes in the treated group. In contrast, the cell cycle time and the intermitotic phase times were not significantly different in the treated and untreated groups at comparable volumes. The increase in the growth rate in AMLS treated mice was obtained in spite of decreases in both the rate constant for cell production and the growth fraction, and was due to a marked decrease in the rate constant for cell loss.
THE PROLIFERATIVE STATUS OF INTESTINAL EPITHELIAL CLONOGENIC CELLS: SENSITIVITY TO S PHASE SPECIFIC CYTOTOXI CAGENTS
Authors: Boarder T. A. , Blackett N. M.
Published: May 2008

High concentrations of tritiated thymidine and cytosine arabinoside (Ara‐C) have been used to selectively kill cells in the crypts of Lieberkuhn that are synthesizing DNA. The effect of these agents on the number of regenerating microcolonies seen 3‐J days after a range of radiation doses indicates that a majority of the clono‐genic cells are proliferating rapidly and that the slowly proliferating cells at the base of the crypt do not represent the whole clonogenic population.
RAPID CELL CYCLE ANALYSIS BY MEASUREMENT OF THE RADIOACTIVITY PER CELL IN A NARROW WINDOW IN S PHASE (RCSi)
Authors: Gray J. W. , Carver June H. , George Yolanda S. , Mendelsohn M. L.
Published: May 2008

A new rapid method for the cell cycle analysis of asynchronously growing cells is presented. The new method is an alternative to the more time consuming and subjective fraction of labeled mitoses (FLM) method. Like the FLM method, all cells in the S phase of the cell cycle are marked by pulse labeling with a radioactive DNA precursor. The subsequent progress of the cohort of cells thus labeled is monitored through a narrow window in the cell cycle. The window is defined by a narrow range of DNA contents corresponding to cells in mid‐S phase and is designated Si. The cellular DNA content is measured by flow cytometry and the cells in the window Si are selected by electronic cell sorting. The radioactivity per cell in Si (RCSi) is determined by liquid scintillation counting. The duration of S phase and of the total cycle and the dispersions therein are determined from the oscillation of the RCSi values with time. The complete cell cycle analysis can be accomplished in as little as 1 day following the collection of samples.

Exponentially growing Chinese hamster ovary (CHO) cells were analyzed according to the RCSi method and the FLM method. It is demonstrated that the two techniques give essentially the same results.
THE KINETICS OF CONTACT INHIBITION IN MAMMALIAN CELLS
Authors: Schmialek P. , Geyer Astrid , Miosga Verena , Nündel M. , Zapf B.
Published: May 2008

To elucidate the process of contact inhibition in mammalian cells, we investigated the kinetics of growth arrest in [3H]thymidine labelled embryonic chinese hamster (Cricetulus griseus L.) cells after the addition of various concentrations of unlabelled cells. It was observed that after the contact inhibition concentration had been reached, the cells grew undisturbed for one more generation. In the following 24 hr the concentration fell back to the level at the beginning of the experiment and stayed there.
SPECIFIC INHIBITION OF CELL PROLIFERATION IN THE MOUSE INTESTINE BY AN AQUEOUS EXTRACT OF RABBIT SMALL INTESTINE
Authors: Sassier P. , Bergeron M.
Published: May 2008

An aqueous extract was prepared from the mucosa of rabbit small intestine by homogenization and centrifugation at 105,000 g. After precipitation with ammonium sulfate, the 0–50 fraction (F1) and the supernatant (F2) were collected, dialysed against a phosphate buffer and tested on rats in vitro and mice in vivo.

The F1 fraction was found to inhibit thymidine incorporation into rat intestinal DNA in vitro, but this effect was not found to be tissue specific (liver, kidney).

Two hours after a single injection of F1 (10 mg protein content), the uptake of tritiated thymidine was decreased in jejunal and colonic DNA in mice. This effect was maximal between 2 and 4 hr and totally reversible after 7 hr; this effect was found in neither the kidney nor the testis. A slowing of cellular migration was also noticed in the jejunum and the colon.

Conversely, the F2 fraction did not inhibit the synthesis of jejunal and colonic DNA either in vitro or in vivo.

Our results suggest that the F1 fraction of the aqueous extract of rabbit small intestine contains one or more substances which may act either on intestinal DNA synthesis or on the G1–S transition of the cellular cycle in the mouse intestine. This reversible and specific intestinal action appears to inhibit cell proliferation and presents several of the characteristics defining a chalone.
PLANNING THE SUICIDE EXPERIMENTS
Authors: Hazout S. , Valleron A.‐J.
Published: May 2008

Suicide experiments involve a great degree of uncertainty in the counting of cell colonies. This work studies from a statistical point of view the precision of the estimation as a function of the number of experimental units which are used. Assuming that the colony numbers in recipients follow a Poisson distribution, we give the necessary number of recipients (a) to determine with a given accuracy the percentage of DNA synthesizing cells (S cells), (b) to test whether or not a cell population is quiescent, and (c) to compare the percentages of S cells in two cell populations.
CELL LOSS FROM SEVERAL TYPES OF SOLID MURTNE TUMOUR: COMPARISON OF 125I‐IODODEOXYURIDINE AND TRITIATED THYMIDINE METHODS
Authors: Begg A. C.
Published: May 2008

The method of measuring tumour cell loss rates in situ following radioactivity loss after a single injection of 125I‐iododeoxyurudine (125I‐UdR) was tested for its accuracy in five different types of murine tumour. To achieve this the method was compared with two others: (1) using 125I‐UdR, but excising tumours before the radioactivity determinations, with or without extracting DNA; (2) using tritiated thymidine and autoradiography. A third method was used on three of the tumours, in which 125I‐UdR‐labelled tumours were grown in unlabelled hosts, followed by whole body counting of the tumour‐bearing mice.

In two of the tumours an increase was observed in total tumour radioactivity with time after 125I‐UdR injection. This prevented the estimation of cell loss parameters in these tumours. Approximately half the increase was due to reutilization of 125I‐UdR supplied from tissues within the mouse; approximately a third to an influx of labelled inflammatory cells (probably in response to infection accompanying ulceration of overlying skin); and the remainder to an increase in non‐DNA radioactivity. In these tumours cell loss rates could be obtained from the whole body counting technique in which influxes of labelled cells and reutilizable radioactivity were eliminated.

A comparison of either 125I‐UdR technique with the 3H‐TdR technique showed good agreement of the cell loss factors for the low cell loss tumours. However, for tumours with high cell loss factors the 125I‐UdR technique gave lower values for cell loss. This implied that reutilization of 125I‐UdR within the tumour (i.e. from internal, not external sources) occurred in the high cell loss tumours.

It is concluded that equating radioactivity loss with cell loss after an injection of 125I‐UdR is reasonable for some tumours, but will result in significant underestimates in others. For high cell loss tumours the 3H‐TdR technique will give the
CELL LOSS FROM THREE ESTABLISHED LINES OF THE C3H MOUSE MAMMARY TUMOR: A COMPARISON OF THE 125I‐UdR AND THE 3H‐TdR‐AUTORADIOGRAPHIC METHODS
Authors: Dethlefsen L. A. , Sorenson J. , Snively J.
Published: May 2008

The125I‐UdR method for measuring cell loss from solid tumors has been re‐evaluated. The rate of tumor cell loss from three established lines (S102F, S102S and Slow) of the C3H mouse mammary tumor was determined by the 125I‐UdRmethod and the results were compared to the estimates for cell loss as determined by the combined approach of cellular 3H‐TdR autoradiography and volumetric growth‐rate determinations. This detailed comparison shows that the two methods complement each other but cannot substitute for one another because they give different quantitative information. The combined approach measures the flow of viable cells, as determined morphologically, from the proliferating compartment to the quiescent compartment, the quiescent compartment out of the tumor, etc., but does not evaluate the flow of degenerate cells or acellular (necrotic) debris. In contrast, the 125I‐UdR method indicates the net flow of intact cells and/or dead cells as well as debris from the tumor as the I25l‐labeled material is lost from the tumor, but gives limited internal information. Thus, depending on the specific experiment, an investigator could choose one or the other of the methods to answer the question. Perhaps both would be desirable at times; however, in most cases, one could not substitute one method for the other. The data from the Slow tumors also indicate that in certain tumors, the quantitative information from the 125I‐UdR method may be quite limited, i.e. the confidence limits within an experiment as well as the replication error between experiments may be high.
GRAIN COUNT THRESHOLD DEPENDENCE OF FLM CURVE PATTERN AND CELL CYCLE PARAMETERS OF HEPATOCYTES IN VIVO
Authors: Wirsching Rainer , Rabes Hartmut M.
Published: May 2008

FLM curves from hepatocytes of regenerating rat liver in vivo were compared at different grain count thresholds. Estimates of cell cycle phases derived from curves with thresholds decreasing from 15 to 1 grain (background 0.2 grains per nuclear area) revealed a prolongation of ts from 6.6 to 9.5 hr, at the expense of tG2M, and tG1, whereas tc remained constant. A similar pattern was observed in FLM curves at various threshold levels for hepatocytes localized in subunits of the liver lobule along the vascular axis from afferent to efferent pole. The shapes of these FLM curves indicated an intralobular gradient of reutilizable labelled material.

The use of two different threshold levels is crucial for proper selection of FLM curves to evaluate cell cycle phases in regenerating rat liver: first, a threshold to exclude the autoradiographic background, and a second one to avoid errors due to reutilization of labelled DNA precursors. Each threshold has its own implications for the estimation of cell cycle phases.
Effect of Myleran On Murine Hemopoiesis
Authors: Delmonte L. , Williams N. , Moore M. A. S.
Published: May 2008

Spleen colony forming cells (CFU‐S) and agar‐gel colony forming cells (CFU‐C) are separate but heterogeneous cell populations, as measured by buoyant density. Myleran (MY) abrogated the major (lighter density) components of the CFU‐S and CFU‐C compartments, thus shifting the surviving CFU‐S and CFU‐C density profiles into the higher density region. the normal spleen colony erythrocytic: granulocytic (E:G) ratio profile showed three density regions with different distributions of erythroid and granulocytic colonies. the preponderantly erythrocytic colony‐generating CFU‐S of the intermediate density regions were eradicated by MY. Comparison of the density distribution of erythrocytic and granulocytic colony‐generating CFU‐S of normal bone marrow showed that the erythrocytic CFU‐S profile paralleled that of total CFU‐S, while most of the granulocytic CFU‐S were contained in the major (and lowest density) peak. MY eradicated the two main (and lowest density) peaks of CFU‐S; surviving CFU‐S occurred preponderantly in a minor (higher density) peak which has a high potential for generating erythrocytic colonies.
An Iron Requirement For the Synchronous Progression of Colonic Cells Following Fasting and Refeeding
Authors: Stragand J. J. , Hagemann R. F.
Published: May 2008

Evidence is presented to show dietary iron to be a major co‐factor in the colonic hyperplasia observed following fasting and refeeding. the iron component serves to remove a fasting induced colonic G1 cycle block and produce the resultant synchronous progression of cells through the cycle. Deleting iion from the refed diet results in no colonic hyperplasia and/or synchronous progression of cells. the results are discussed from the viewpoint of colonic steady state cell renewal and as a possible tool for the study of in vivo steady state cell renewal.
Pluripotent (Cfu‐S) and Granulocyte‐Committed (Cfu‐C) Stem Cells In Intact and 89Sr Marrow‐Ablated S1/S1D Mice
Authors: Adler S. S. , Trobaugh F. E.
Published: May 2008

Peripheral blood values, femur cell counts, spleen weights, pluripotent (CFU‐S) and granulocyte progenitor cell (CFU‐C) concentrations and total content of spleens and femurs have been evaluated in intact (non‐marrow‐ablated) and 89Sr marrow‐ablated S1/S1d and +/+ mice. 89Sr‐irradiated mice were studied 6 and 11 days after the administration of 89Sr. In intact S1/S1d mice the femur CFU‐S concentration, total femur CFU‐S, femur CFU‐C concentration and total femur CFU‐C were 84, 54, 105 and 68% that of +/+ mice femurs respectively; the respective values for the spleens of S1/S1d mice were 40,46,61 and 69%. These are the first simultaneous determinations of CFU‐S and CFU‐C concentrations, and content of spleens and marrows, of S1/S1d and +/+ mice. In 89Sr marrow‐ablated mice, 11 days after injection of the radionuclide: (a) the total content of marrow CFU‐C and CFU‐S was about 1% of that found in the marrows of intact mice for both +/+ and S1/S1d groups; (b) the spleens of +/+ mice increased in weight to 162% of the control, but the spleens of S1/S1d mice did not increase in weight; and (c) the spleens of +/+ mice had a total content of CFU‐C and CFU‐S of 800% and 260% of the control, respectively, whereas the respective values for the S1/S1d mice were 120% and 76% of the control. Thus the S1/S1d spleen fails to compensate for marrow ablation by housing additional CFU‐S and has an impaired ability to compensate by housing additional CFU‐C.
Removal of the Horny Layer Does Not Stimulate Cell Proliferation In Neonatal Mouse Epidermis
Authors: Bertsch S. , Marks F.
Published: May 2008

Mechanical treatment of newborn mouse back skin by removal of the horny layer does not stimulate DNA synthesis and mitotic activity. These results are discussed in connection with recent experiments with newborn and adult mouse epidermis, and reveal further evidences for the ontogenetic development of an endogenous growth control (chalones).
EFFECT of DOUBLE PARTIAL HEPATECTOMIES AT VARIOUS INTERVALS ON [3H]THYMIDINE INCORPORATION INTO RAT LIVER DNA
Authors: Honda S. , Hirose S.
Published: May 2008

At various intervals after a 34% hepatectomy, another 34% (50% of the remnant) hepatectomy was performed on rats, and the [3H]thymidine incorporation into the DNA of remaining liver cells was measured 24 hr after the first operation. the values of [3H]thymidine incorporation into liver DNA of rats hepatectomized doubly (34% and 34%) at 6, 8 and 10 hr intervals were greater than the sum of the value of rats which received a single 34% hepatectomy at the start and those of rats which received a single 68% hepatectomy at 6, 8 and 10 hr, respectively.
QUANTIFICATION OF ENTRY INTO AND EXIT FROM THE CELL CYCLE IN HUMAN LYMPHOCYTE CULTURES
Authors: Dorian R. , Bernheim J. L. , Mendelsohn J.
Published: May 2008

A mathematical model is presented for the analysis of transition between cycling and non‐cycling compartments by cells responding to a growth stimulus. the cellular age distribution as a function of time is derived from sequential [3H]thymidine pulse labeling indices. Rates of entry into and exit from the cycling compartment are determined on the basis of labeling indices obtained after instantaneous and long duration [3H]thymidine pulses. Analysis of an experiment involving sequential measurements over the whole lifespan of a human lymphocyte culture stimulated by phytohemagglutinin is presented as an example of the application of this method.
A SIMPLE METHOD FOR PRODUCING DIFFERENT GROWTH FRACTIONS IN VITRO FOR USE IN ANTI‐CANCER DRUG STUDIES
Authors: Barranco S. C. , Bolton W. E. , Novak J. K.
Published: May 2008

A simple technique has been used experimentally to produce in vitro Chinese hamster ovary cells with growth fractions ranging from 0 to 100%. Known numbers of exponentially growing and plateau‐phase tissue culture cells were mixed in various proportions to yield the desired final growth fraction. Cells attach to the culture flask surface within 1 hr of mixing. Treatment at that time with the nitrosourea compounds, CCNU and MeCCNU, resulted in differential drug survival sensitivities that were dependent upon the growth fraction of the population treated.
FAILURE TO IDENTIFY A SPERMATOGONIAL CHALONE IN ADULT IRRADIATED TESTES
Authors: Cunningham G. R. , Huckins Claire
Published: May 2008

The adult irradiated rat testis was used as a model system to confirm the existence of a spermatogonial chalone. Rats were given 330 rad whole body 60Co irradiation, a dose which selectively destroys most of the spermatogonial population except for the radioresistant As stem cells. 11 days after irradiation, when spermatogonial numbers were minimal, the rats were injected with a testicular or liver extract prepared from normal adult rats, or with saline. Each group received a total of four injections given at 4 hr intervals. 2 hr before death, the animals were injected with [3H]TdR. Testicular DNA was isolated and the incorporation of [3H]TdR was determined. The mean ± s.e. ct/min per μg DNA in rats given testicular extract (9·38 ± 0·94) was no different than in those receiving liver extract (10·43 ± 2·01) or saline (7·23 ± 0·69). Autoradiographic studies indicated that variability in counts within or between groups could be attributed to variations in the number of pre‐leptotene spermatocytes which incorporated [3H]TdR for the meiotic divisions. Quantitatively, there were no differences between groups in terms of the numbers of A spermatogonia, their labelling indices, or mitotic activity. Therefore, the presence of a spermatogonial chalone could not be demonstrated using crude extracts from normal testes in this irradiated model.
REGENERATIVE PROLIFERATION OF MOUSE EPIDERMAL CELLS FOLLOWING APPLICATION OF A SKIN IRRITANT (CANTHARIDIN)
Authors: Clausen O. P. F.
Published: May 2008

The strong skin irritant cantharidin dissolved in benzene was applied to the back of hairless mice. Single cell suspensions of epidermal basal cells were obtained and flow microfluorometric measurements of cellular DNA content were made. Smears were made for autoradiography, and the [3H]TdR labelling index (LI) and mean grain count (MGC) were assessed up to 3 days after cantharidin application.

Three successive peaks of cells with S phase DNA content accompanied by three LI peaks were observed. The first two peaks were follwed by peaks of cells in G2 phase, indicating that after the acute cell injury caused by cantharidin the cells traversed the cell cycle in partial synchrony through two subsequent cell cycles, each of 10–12 hr duration. During this phase of rapid proliferation the LI reached the proportion of cells in S phase, contrary to what is observed in untreated mouse epidermis, where the labelled cells contribute to about half the proportion of cells with S phase DNA content. The first two peaks of cells in S phase and LI coincided with an increased MGC, whereas the third peak was accompanied by a MGC significantly below control values. This indicates that this latter peak is due to a longer DNA synthesis time rather than to a partially synchronized and increased cell proliferation. The duration of the G1, S and G2 phases seems to be reduced initially in rapidly proliferating epidermis.
VIABILITY OF THE CERVICAL EPITHELIUM DURING CARCINOGENESIS IN MICE
Authors: Rubio C. A. , Skoog L. , Fox C. H.
Published: May 2008

Autoradiograms of histological specimens from the cervix of seventy‐five mice were analysed after in vivo injection with an RNA precursor. All nucleated, non‐pyknotic cells and some mitotic figures were labelled, which suggested that the tissue was metabolically active (i.e. viable). Only the uppermost epithelial pyknotic cells were devitalized, as deduced by the morphological appearance of the cells and by the absence of label. The viability of the whole epithelium suggests that the previously reported focal distribution of proliferating and non‐proliferating areas in the cervical epithelium of mice is a genuine phenomenon.
TESTOSTERONE‐INDUCED CELL PROLIFERATION IN THE ACCESSORY SEX GLANDS OF MICE AT VARIOUS TIMES AFTER CASTRATION
Authors: Alison M. R. , Wright N. A.
Published: May 2008

The proliferative response to testosterone in the accessory sex glands (seminal vesicle and coagulating gland) of castrated male Balb/c mice has been examined by pulse and continuous thymidine‐labelling experiments, and by the fraction of labelled mitoses technique. Progressive reductions in cellularity followed castration, and by varying the time elapsing between castration and the initiation of testosterone treatment, it was clear that the size of the response depended upon the number of cells in the tissue, relative to the normal complement.

Interpretation of FLM data was difficult in periods where proliferative rates changed rapidly. We have attempted to explain the cell kinetic events by postulating a G0 compartment, from which cells are stimulated to enter the proliferative cycle before subsequently returning to an out of cycle state. It was thought unlikely that substantial changes in cell cycle time occurred.

In both the accessory sex glands, the overall form of the continuous thymidine labelling curves showed that most proliferative cells entered DNA synthesis in a shorter time after stimulation at 14 days after castration than they did at 3 days after castration. The data were not consistent with cells moving deeper into G0 with time after castration. In the seminal vesicle almost all epithelial cells were potentially proliferative by 3 days after castration. In the coagulating gland only 30% were potentially proliferative at 3 days, increasing to 85% at 14 days after castration. However, such proportional increases represented much smaller changes in terms of absolute numbers of cells, because of a concomitant decline in cellularity from 3 to 14 days after castration.
DIFFERENTIAL LETHAL EFFECTS OF BOTH CYTOSINE ARABINOSIDE AND HYDROXYUREA ON JEJUNAL CRYPT CELLS AND TESTOSTERONE‐STIMULATED ACCESSORY SEX GLANDS
Authors: Alison M. R. , Wright N. A.
Published: May 2008

DNA‐synthesizing cells from mouse jejunal crypts and accessory sex glands respond differently to the DNA synthesis inhibitors cytosine arabinoside and hydroxyurea. A single injection of either agent brought about a rapid inhibition of thymidine labelling in both the tissues. Whilst both agents had a lethal effect upon the majority of S‐phase cells in the crypts, only a minority of S‐phase cells in the accessory sex glands showed evidence of necrosis. These differences are considered in the context of possible physiological differences between continually dividing cells and putative G0 cells. The accessory sex glands are normally quiescent proliferative tissues. They were stimulated to undergo DNA synthesis and later mitosis by testosterone propionate injections, commencing three days after castration. Cytosine arabinoside was the more effective cytocidal agent in the accessory sex glands, and when two injections were scheduled so as to affect a large number of DNA‐synthesizing cells, a compensatory hyperplasia was evoked. In the coagulating gland, this compensatory response involved the proliferation of many cells which, in the absence of cytotoxic perturbation, would be non‐proliferative (Q cells).
INDUCTION OF ERYTHROPOIETIN RESPONSIVENESS IN VITRO BY A DISTINCT POPULATION OF BONE MARROW CELLS
Authors: Wagemaker G. , Peters M. F. , Bol S. J. L.
Published: May 2008

Bone marrow contains a small population of primitive erythroid progenitor cells which can be detected by their capacity to form large numbers of erythroid progeny in viscous cultures containing erythropoietin (EP). These cells have been termed erythroid ‘burst‐forming units’(BFUe). The present study demonstrates that expression of the erythroid differentiation potential of BFUe requires the presence of an activity additional to EP. This activity has been designated as BFA (burst feeder activity). It is shown that the number of BFUe detected and their apparent sensitivity to EP are directly related to the BFA concentration of the cultures.

BFA was found to be associated with a population of bone marrow cells of high buoyant density and small volume, which are sensitive to irradiation. The radiation dose‐effect curve provided strong evidence that bone marrow BFA is independent of cell proliferation; this was supported by showing that BFA is unaffected by in vivo treatment with hydroxyurea.

The findings are compatible with a two‐step regulation model for erythroid differentiation in which BFA‐induced progeny of BFUe acquire sensitivity to EP.
PARTICLE‐INDUCED ERYTHROPOIETIN‐INDEPENDENT EFFECTS ON ERYTHROID PRECURSOR CELLS IN MURINE BONE MARROW
Authors: Ploemacher R. E. , van Soest P. L. , Wagemaker G. , van't Hull E.
Published: May 2008

A possible regulatory action of phagocytic cells on erythropoiesis was investigated by infusion of inert polystyrene latex particles (LAT). LAT appeared to induce changes in the femoral content of erythroid progenitor cells. These changes were most pronounced in primitive erythroid progenitor cells (BFUe) and appeared to be gradually damped in more differentiated populations (CFUe and erythroblasts). LAT did not influence granulocyte/macrophage progenitor cells (CFUc). The effects of LAT could not be attributed to changes in the systemic erythropoietin (EP) concentration. Administration of dexamethason nullified the effect of low doses of LAT, suggesting that phagocytosis of the particles is essential to the observed effects.

Erythroid burst formation was previously found to be dependent on a bone marrow associated activity, termed BFA (burst feeder activity). BFA acts as an in vitro inducer of EP‐responsiveness in BFUe. In this study it was found that LAT‐induced changes in femoral erythroid progenitor cell content were characteristically preceded by corresponding changes in BFA. It was concluded that BFA‐associated cells probably play a role in vivo in the early differentiation of erythroid progenitor cells.

The present data are interpreted as direct in vivo evidence supporting a two‐step regulatory model operating in erythropoiesis and provide evidence that phagocytic cells are a component of the erythroid haemopoietic inductive micro‐environment.
A MATHEMATICAL MODEL OF THROMBOPOIESIS IN RATS
Authors: Wichmann H.‐E. , Gerhardts M. D. , Spechtmeyer H. , Gross R.
Published: May 2008

A mathematical model of thrombopoiesis in rats is presented. This has four compartments; stem cells, megakaryocytes, thrombocytes and thrombopoietin. A high thrombopoietin concentration influences bone marrow proliferation in three ways. Firstly the stem cells are stimulated and a slow increase in megakaryocyte number follows. Secondly there are additional endomitoses in the (early) megakaryocytes resulting in an increase in megakaryocyte volume. Thirdly the megakaryocyte maturation time is shortened. The parameters of the model are determined from experimental values for the normal, maximum and minimum proliferation rates, maturation times and destruction rates. The model is tested by comparing simulated results for acute and chronic thrombocytopenia and thrombocytosis with experimental curves from the literature. The model and data agree within the limits of experimental error. Not all of the thrombopoietic regulatory system is known yet, so some important alternative hypotheses are investigated and compared with the model. Several hypotheses have been excluded in this way.
BUOYANT DENSITY ANALYSIS OF MYELOID COLONY‐FORMING CELLS IN GERMFREE AND CONVENTIONAL MICE
Authors: Byrne P. V. , Heit Hildegard , Heit W.
Published: May 2008

Granulocyte‐macrophage colony‐forming cells (CFUc), in the bone marrow of germfree and conventional CBA mice, were compared quantitatively and qualitatively. Cells were separated on the basis of their buoyant density by equilibrium centrifugation in continuous albumin density gradients. CFUc in the density subpopulations were detected by culture in agar containing three different types of colony stimulating factor (CSF). The sources of the CSF were post‐endotoxin mouse serum (CSFES), mouse lung conditioned medium (CSFMLCM) and human urine (CSFHU). Mice were removed from the germfree environment and the buoyant density status of their CFUc was examined 1, 4 and 8 weeks later.

No difference was found between germfree and conventional mice in the number of nucleated cells per femur or in their modal density. Neither was the number of CFUc per femur different. The cell cycle status of CFUc, as determined by the thymidine suicide technique was not significantly different.

Functional heterogeneity was found among the density subpopulations for both groups of mice. This depended on the type of CSF.

The density distribution of CFUc was significantly different in germfree mice. There were proportionately more low density CFUc. The mean modal density of CFUc under CSFES stimulation was less by 0.0045 g/cm3 in germfree mice.

The removal of mice from the germfree environment resulted in a shift of the distribution to higher densities. The trend was towards the conventional situation. The significance of the buoyant density status of CFUc is discussed.
THE PROLIFERATIVE STATE OF GRANULOCYTIC PROGENITOR CELLS IN HUMAN BLOOD AND MARROW
Authors: Standen G. , Philip M. A. , Fletcher J.
Published: May 2008

A double layer agar technique was used to investigate the proliferative state of granulocytic progenitor cells (Colony Forming Units in Culture; CFUc) in human peripheral blood and bone marrow. The sensitivity of the progenitor cells to the S‐phase specific agent, hydroxyurea, was used as an index of the proportion of cells engaged in DNA synthesis. In the presence of low concentrations of colony stimulating factor (CSF) the CFUc were found to be virtually insensitive to the drug. However, when cultured in the presence of increasing concentrations of CSF the proportion of CFUc apparently killed by hydroxyurea increased to a maximum of 23% for those cells in the blood and 39% for those in the marrow. The results indicate that CFUc which are slowly proliferating are sensitive to low concentrations of CSF. In contrast, those CFUc which are proliferating more rapidly require high concentrations of CSF before they will form colonies in culture. A model has been devised which suggests that as CFUc mature, their cell cycle time shortens and their sensitivity to CSF decreases.
MATRIX ALGEBRAIC SIMULATION OF MITOTIC CELL SELECTION EXPERIMENTS
Authors: Tomasovic S. P. , Roti J. L. Roti , Dethlefsen L. A.
Published: May 2008

Mitotic cell selection experiments are frequently utilized in investigations on the effects of various metabolic inhibitors and/or X‐irradiation on cell‐cycle progression of mammalian cells in tissue culture. This study describes a method for matrix algebraic simulation of these experiments which involves the sequential multiplication of cell‐population matrices, growth matrices, and mitotic cell‐selection matrices. Simulations are shown for progression in control cultures and cultures perturbed either by X‐rays or 2‐mercapto‐1(β‐4‐pyridethyl) benzimidazole. Application of this model will enhance the planning of these investigations and allow more rigorous testing of alternate hypotheses concerning the mechanisms of action of perturbing agents.
IN VITRO PROLIFERATION OF MOUSE LYMPHOBLASTOID CELL LINES: GROWTH MODULATION BY VARIOUS POPULATIONS OF ADHERENT CELLS
Authors: Zipori D.
Published: May 2008

The in vitro growth pattern of a number of mouse lymphoblastoid tumour cell lines was modified in the presence of adherent cell layers from various sources. The AVRij‐1 and ST‐4b cell lines exhibited a concentration—dependent growth pattern, i.e., they would only grow well when seeded at high starting cell concentrations. Better growth of these cells from low cell concentrations was observed in the presence of adherent cell layers from syngeneic or allogeneic bone marrow. Adherent cell layers derived from mouse spleen and pleural or peritoneal cavity could also promote the growth of the above tumour cells, but in a narrower range of cell concentrations and to a lower extent. Moreover, confluent adherent layers from the pleural and peritoneal cavities completely inhibited the growth of AVRij‐1 and ST‐4b cells, while adherent cell layers from the bone marrow did not inhibit growth at any cell concentration tested. The in vitro growth of concentration—independent cell lines was also affected by the presence of adherent cells from the bone marrow. Under syngeneic conditions, a slight increase in the growth of the ‘null’ or pre‐B lymphoma cell line ABLS‐8.1 was observed. On the other hand, the growth of tumour cells expressing more differentiated properties, such as the thymus T lymphoma tumour cell line ST‐1.3 and the plasma cell tumour MPC‐11.45.6.2.4, was inhibited in the presence of syngeneic bone marrow derived adherent cell layers. This inhibition was more pronounced under allogeneic conditions. Growth inhibition was also observed when concentration—independent cell lines were co‐cultured with adherent cells from the pleural and peritoneal cavities. Thus, adherent cell layers from non‐haemopoietic sources inhibited the growth of all cell lines tested. On the other hand, adherent cells from the bone marrow had a differential effect on growth of lymphoblastoid tumour cell lines. This depended on the in vitro growth properties of each tumour cell line and on some additional specific tumour cell properties. The latter could relate to the differentiation stage characterizing each tumour cell line. The culture method described here may serve as a model system for studies on interaction of leukaemic cell and the haemopoietic microenvironment.
DIFFERENT LABELLING PATTERNS IN MOUSE LYMPHOID TISSUES WITH [3H]DEOXYCYTIDINE AND [3H]THYMIDINE
Authors: Hamatani K. , Amano M.
Published: May 2008

The percentages of labelled lymphocytes in smear preparations of mouse thymus were higher than those in similar preparations of mesenteric lymph nodes with either generally labelled tritiated deoxycytidine, [3H]CdR, or tritiated thymidine, [3H]TdR. Lymphocytes in the thymus cortex and in germinal centres of mesenteric lymph nodes were intensely labelled with [3H]CdR, whereas with [3H]TdR lymphocytes in the peripheral region of thymus and medullary cords of mesenteric lymph nodes were heavily labelled. The majority of lymphocytes in thymic cortex and germinal centres of mesenteric lymph nodes were labelled weakly with [3H]TdR. Thus, labelling patterns with [3H]CdR differed from those with [3H]TdR in lymphoid tissues of the mouse.

Mouse lymphocytes can utilize [3H]CdR as a precursor molecule for cytosine and thymine in DNA. The ratio of radioactivity of thymine to that of cytosine was measured biochemically in DNA extracted from lymphocytes labelled with [3H]CdR. This radioactivity ratio in thymus was higher than that in mesenteric lymph nodes. These results suggest that the metabolic activities of utilizing CdR for DNA synthesis differ within lymphocyte populations in various lymphoid tissues in the mouse.
DETERMINATION OF NON‐PROLIFERATING CELLS IN CULTURE BY COMBINING FLOW CYTOMETRY WITH STATHMOKINETICS
Authors: Böhmer R.‐M.
Published: May 2008

Colcemid was added to the growth medium of L‐cells in monolayer culture. The proliferating cells continued their progression through the cycle up to metaphase, where they were arrested. At different times after Colcemid addition the cells were trypsinized. suspended immediately in a solution of the DNA‐specific fluorescent dye Hoechst 33258 and analysed with a flow cytometer. The histograms were evaluated to give the fraction of cells in the 2c peak as a function of time after Colcemid addition. The flux into the 2c compartment being interrupted, the peak content decreased until all proliferating (G1) cells had entered S‐phase. With increasing cell density or with increasing time after serum deprivation an increasing fraction of cells remained in the 2c peak at times greater than the normal G1 duration. The possibility of applying this method to the determination of non‐proliferating cells in a population is discussed.
CELL KINETICS OF IRRADIATED EXPERIMENTAL TUMORS: CELL TRANSITION FROM THE NON‐PROLIFERATING TO THE PROLIFERATING POOL
Authors: Potmesil M. , Goldfeder A.
Published: May 2008

Parenchymal tumor cells of murine mammary carcinomas can be divided into two pools, using nucleoli as morphological ‘markers’. Cells with dense nucleoli traverse the cell cycle and divide, thus constituting the proliferating pool. Cells with trabeculate or ring‐shaped nucleoli either proceed slowly through G1 phase or are arrested in it. The role of these non‐proliferating, G1 phase‐confined cells in tumor regeneration was studied in vivo after a subcurative dose of X‐irradiation in two transplantable tumor lines. Tumor‐bearing mice were continuously injected with methyl[3H]thymidine before and after irradiation. Finally, the labeling was discontinued, mice injected with vincristine sulfate and cells arrested in metaphase were accumulated over a 10‐hr period. Two clearly delineated groups of vincristinearrested mitoses emerged in autoradiograms prepared from tumor tissue at the time of starting tumor regrowth: one group with the silver‐grain counts corresponding to the background level, the other with heavily labeled mitoses. As the only source of unlabeled mitoses was unlabeled G1 phase‐confined cells persisting in the tumor, this observation indicated cell transition from the non‐proliferating to the proliferating pool, which took place in the initial phase of the tumor regrowth. Unlabeled progenitors have apparently remained in G1 phase for at least 5–12 days after irradiation.