bluuebunny/crossref_metadata_2025 huggingface dataset:
POLYMETHACRYLIC ACID: INDUCTION OF LYMPHOCYTOSIS AND TISSUE DISTRIBUTION
Authors: Ross W. M. , Martens A. C. , Bekkum D. W. van
Published: May 2008

Polymethacrylic acid (PMAA) induces up to a three‐fold increase in the lymphocyte population of peripheral blood in rats, goats and calves after intravenous administration. Other routes of administration are less effective. A maximum lymphocytosis is achieved after 3 hr with all doses in excess of 30 mg PMAA/kg body weight; over the next few hours the lymphocyte level declines to normal. Granulocytes increase steadily for the first 7 hr before declining. Multiple doses of PMAA 2 hr apart failed to maintain or significantly alter the lymphocytosis.

PMAA was labelled with 125I and 14C, and was traced to various sites in the rat. The greatest accumulation of radioactivity was in the spleen, lungs, liver, kidney, adrenals and mesenteric lymph nodes (with 14C‐PMAA). The accumulation appeared more specific for spleen and lymph nodes since there was only a small loss of activity following removal of blood by whole body perfusion. This supports previous findings indicating that these two tissues play a major role in the development of lymphocytosis. Accumulation in the bone marrow may be indicative of stem cell mobilization.

The results are discussed in terms of the lymphocytosis‐inducing mechanism and the site of action of PMAA and the possible clinical application to ECIB therapy is considered.
STUDIES ON THE REGULATION OF LYMPHOCYTE PRODUCTION IN THE MURINE THYMUS AND SOME EFFECTS OF A CRUDE THYMUS EXTRACT
Authors: Olsson Lennart , Claësson Mogens H.
Published: May 2008

Cell proliferation in the murine thymus was studied in vivo under normal conditions and from 0 to 24 hr after a single injection of a water‐soluble extract from mouse thymus, mouse spleen, and mouse skin. The thymus extract reduced during the first 24 hr the mitotic activity 40%; the spleen extract had a weaker inhibitory effect. The skin extract had no such effect. The thymus extract and spleen extract inhibited the flux of cells into the S phase 0–8 hr after the injection of the extract. Initial labelling index was also reduced in this period. Eight hours after injection of the thymus or spleen extracts the inhibited cells initiated DNA synthesis. The rate of progression of blast cells through the cell cycle was normal 24 hr after the injection of the extracts.

It was deduced from the analysis that the thymus extract inhibits processes triggering Go/Gi cells into DNA synthesis, the inhibition of G2 efflux being of minor importance. Finally a model for the regulation of proliferating thymic blast cells and the emigration of small lymphocytes from the thymus is proposed.
SPERMATOGENETIC CLONES DEVELOPING FROM REPOPULATING STEM CELLS SURVIVING A HIGH DOSE OF AN ALKYLATING AGENT
Authors: Keulen C. J. G. van , Rooij D. G. de
Published: May 2008

We investigated stem cell renewal and differentiation in 10‐ and 15‐days‐old spermatogonial clones developing in mouse seminiferous epithelium after an extremely large cell loss, inflicted by high doses of the alkylating agent Myleran.

The spermatogonial clones arise from cells that resemble the Ais spermatogonia but have a larger nuclear diameter. In spite of their mitotic activity these ‘re‐populating stem cells’ lie mainly isolated or in pairs. This is explained by migration and differentiation. Migration appeared to occur at random in all directions along the basement membrane of the seminiferous tubule.

After one or more divisions of the stem cells, a second type of cell appears, which is called the ‘differentiating spermatogonium’. The time elapsing before this type of cell appears, depends on the dose of Myleran: the larger the dose the later differentiation starts. A relation could be demonstrated between the stage of the cycle of the seminiferous epithelium and the start of differentiation. Differentiating cells were found isolated or in groups of two, four, eight or sixteen cells. Hence we concluded that at least up to their fourth division differentiating cells divide synchronously without degenerations.

Three types of division of repopulating stem cells were distinguished, producing (1) two repopulating stem cells, (2) one repopulating stem cell and one cell starting spermatogonial differentiation, or (3) two differentiating cells. Type 1 divisions were found most frequently.
THE INFLUENCE OF A GRANULOCYTIC INHIBITOR(S) ON HEMATOPOIESIS IN AN IN VIVO CULTURE SYSTEM
Authors: MacVittie Thomas J. , McCarthy Kenneth F.
Published: May 2008

The in vivo diffusion chamber (DC) technique for mouse marrow culture was used to determine the effect of a granulocyte inhibitor on the proliferation of the pluri‐potent stem cell (CFU‐s) and the granulocyte progenitor cell (CFU‐c). Granulocyte conditioned medium was injected intraperitoneally into mice bearing DCs during the initial 48 hr of culture. The early injection of inhibitor resulted in a significantly reduced number of granulocytic progeny formed within the DCs while there was no growth inhibition of mouse fibroblasts cultured under identical conditions. The reduced cell production was due in part to a significant reduction in the self‐renewal rate of the CFU‐c while no apparent direct effect was observed upon the growth of the CFU‐s within the same cultures.

These data suggest that the granulocytic inhibitor(s) acted to reduce proliferation within the CFU‐c population and thereby diminished the amplification potential inherent in the initial cell inoculum.
INHIBITORY AND ANTI‐INHIBITORY FACTORS OF RAT SERUM ACTIVE ON THE G1‐S TRANSITION OF HEPATOCYTE CELL CYCLE
Authors: Nadal C. , Boffa G. A.
Published: May 2008

Rat hepatocytes are responsive to a serum factor inhibiting their progression through the cell cycle from the late G1 phase to the S phase. After fractionation of normal adult rat serum by two chromatographic steps on DEAE cellulose and sephadex gel filtration, the inhibitory activity was linked to proteins having a high electronegative charge and of apparent high molecular weight. Polyacrylamide gel electrophoretic analysis of active fraction showed that the α1 macroglobulin was its main component. Male and female baby rats were sensitive to the inhibitory factor from normal rats.

Contrary to the normal adult rat serum the whole hepatectomized adult rat serum did not exhibit any inhibitory activity on the G1‐S transition. However, two components having antagonist activities: an α1 globulin and a γ globulin, were separated by chromatographic procedures from hepatectomized rat serum.

The α1 globulin showed an inhibitory activity. It had an apparent molecular weight lower than that found in normal rats. Its activity was sex related: only male baby rats were responsive.

The factor present in the γ globulin fraction was found to be antagonistic to the α1 globulin factor. Its occurrence after hepatectomy explains the absence of inhibitory activity in the serum of hepatectomized rats.
METALLIC COPPER‐INDUCED GRANULOCYTE EXUDATION IN THE STUDY OF GRANULOCYTOPOIESIS
Authors: McGarry Michael P.
Published: May 2008

C3H/HeHa mice implanted with rods of metallic copper (CR) or glass (GR) exudate neutrophil granulocytes and mononuclear cells into the site of rod implant (peritoneal cavity). Exudation in CR mice is substantially greater than in GR animals. In CR mice there is an impressive stimulation of myelopoiesis measured in the femoral marrow subsequent to the initial accumulation in the peritoneal cavity. Serum levels of colony stimulating activity (CSA), an in vitro myeloproliferative stimulating activity, are elevated in such animals, as are femoral marrow agar‐colony forming cells (CFC). The procedure is useful to the study of myelopoiesis and myelopoietic regulatory mechanisms.
CELL POPULATION KINETICS IN THE RAT JEJUNAL CRYPT
Authors: Wright Nicholas A. , Al‐dewachi Huthaifa S. , APPLETON David R. , Watson Alexander J.
Published: May 2008

Cell kinetics in the jejunal crypt of the male Wistar rat were studied using autoradiographic techniques with tritiated thymidine and a stathmokinetic technique with vincristine. The migration rate measured by following the movement of the 50 % peak on the labelling index distribution curve with time after injection of tritiated thymidine gave a value of 1.43 ± 0.14 (SE) cell positions per hour, compared with a value from a cumulative birth rate of 1.78 cell positions per hour.

The crypt column length was 32.9 ± 0.2 cells and the column count was 22.3 ± 0.2. This measurement gave a total crypt population of 734 cells, compared with an estimate of 650 ± 6 from direct observation of squashed, microdissected crypts. In each crypt 22.5 ± 0.5 mitoses were present, and the crypt cell production rate was 32 cells per crypt per hour; this latter value was confirmed using two independent techniques.

The crypt growth fraction calculated from the durations of phases of the cell cycle and the labelling index was 0.62. A value of 0.61 was found from the labelling index distribution curve. As assessed from crypt squashes, there were 403 proliferating cells per crypt.
CELL KINETICS OF IRRADIATED EXPERIMENTAL TUMORS: RELATIONSHIP BETWEEN THE PROLIFERATING AND THE NONPROLIFERATING POOL
Authors: Potmesil Milan , Ludwig Donald , Goldfeder Anna
Published: May 2008

The role of nonproliferating cells in tumor regeneration has been studied after subcurative doses of low L.E.T. irradiation. Radiation was applied in a single dose at three different levels, 0–47, 0–94 and 1–88 krad. Studies included estimation of the absolute number of cells per tumor, differential cell counts, and autoradiographic determination of kinetic variables, employing transplantable mouse mammary adenocarcinoma DBAH.

Quantitative changes of morphologically denned proliferating and non‐proliferating cell pools were followed at different time intervals after irradiation. Irradiation resulted in reduction of the number of cells in both pools, with apparent sparing of nonproliferating cells. The regenerative period started with a gradual increase in the number of cells in the proliferating pool, whereas the number of cells in the nonproliferating pool continued to fall in tumors irradiated with 0–94 and 1 ‐88 krad. In the late phase of tumor regrowth, the increasing number of cells in the non proliferating pool corresponded to its replenishment by cell transition from the proliferating pool.

In an effort to clarify whether cell transition from the nonproliferating to the proliferating pool may take place during the regrowth of radiation perturbed tumors, cell loss rates from both pools were estimated using experimental data. In addition to cell losses from the tumor as a whole, the ‘net loss rate’ of the non‐proliferating pool reflects the rate of cell transition from the nonproliferating to the proliferating pool, minus the rate of transition in the opposite direction. A similar definition applies to cell loss rates from the proliferating pool. The results showed: (1) high losses in both pools, with excess losses in the proliferating during the early phase after irradiation; (2) in the early stage of regrowth after irradiation, the cell net loss rate for the nonproliferating pool increased, in contrast to the behavior of cell loss rate for the proliferating pool and the average cell loss rate for the tumor as a whole; (3) in the late stage of regrowth a decrease in net loss rate for the nonproliferating pool reflects the excess production of nonproliferating cells over control tumors. These results suggest that cell transition from the nonproliferating to the proliferating pool takes place at the beginning of tumor regrowth after subcurative single‐dose irradiation.
THE INFLUENCE OF 400 R X‐IRRADIATION ON THE NUMBER and THE OCALIZATION OF MATURE and IMMATURE GOBLET CELLS and PANETH CELLS IN INTESTINAL CRYPT and VILLUS
Authors: Dongen J. M. VAN , Kooyman J. , Visser W. J.
Published: May 2008

The influence of 400 R X‐irradiation on the localization and the number of mature and immature goblet cells and Paneth cells in rat duodenal epithelium has been studied. At short times after irradiation, when the total proliferative activity in the crypts of Lieberkiihn is reduced, the proportion of mature and immature goblet cells of the total number of crypt cells was increased; also an absolute increase in the number of goblet cells in the crypts was found. The immature goblet cells were localized in the lower half of the crypt as in control animals, whereas the number of the mature cells increased over the whole crypt length. When the proliferative activity of the crypt cells increases again from 12 to 48 hr after irradiation the number of both types of goblet cells decreases. Between 48 and 72 hr, when the whole crypt is involved in proliferation, a second increase of both types of goblet cells was found. However, the localization of the immature goblet cells is no longer restricted to the lower half of the crypt but they also appear at the higher cell positions.

On the villus no immature goblet cells were found and the changes in the numbers of mature goblet cells do reflect the changes induced by irradiation in the goblet cell population in the crypt. The absolute number and localization of Paneth cells did not change under the experimental conditions. The findings are discussed in relation to cell proliferation and differentiation processes in intestinal crypts.
EFFECT OF A SPERMATOGONIAL CHALONE ON THE GROWING RAT TESTIS
Authors: Clermont Y. , Mauger A.
Published: May 2008

Immature rats were used in an experiment to test the possible influence of a spermatogonial chalone on the expanding spermatogonial population in their developing testes. An extract from adult rat testes was injected intraperitoneally into 33‐day‐old rats and control animals were injected with an equal amount of saline. Two groups of normal adult rats similarly injected with the testicular extract and saline solutions served as additional controls. Following these injections, all animals were administered a dose of 3H‐thymidine 10 hr before sacrifice. An analysis of the labeling indices of the various types of spermatogonia revealed that in young rats injected with testicular extract the percentage of labeled type A spermatogonia was significantly lower than in control animals. In contrast, the labeling indices of Intermediate and type B spermatogonia were similar in the two groups of young rats. In the two groups of adult animals, there was no difference in the labeling indices of type A or of other types of spermatogonia. These data indicated that the saline extract of adult testes contained a substance, a spermatogonial chalone, inhibiting specifically the proliferation of some type A spermatogonia. The results also support the concept that a spermatogonial chalone may intervene, through its action on the spermatogonial stem cell population, to arrest the growth of the seminiferous tubules as the animal reaches maturity.
THE PREDOMINANT ROLE OF THE SPLEEN IN LYMPHOCYTE RECIRCULATION
Authors: Pabst R. , Trepel F.
Published: May 2008

Autologous blood lymphocytes from three normal pigs were labelled with 3H‐uridine and retransfused before and after splenectomy. Frequent samples for up to 150 min after retransfusion were evaluated autoradiographically to determine the rate of disappearance of labelled lymphocytes from the blood. In one pig retransfusion was performed before and after sham‐splenectomy.

In all preoperative experiments the pattern of disappearance of labelled lymphocytes was very similar. After a first rapid decline (halving time on average 8 min) a short rise of the labelling index was observed from 10 to 15 min after retransfusion. Then a second more gradual decrease of labelled lymphocytes followed. The mean halving time during this period was less than 32 min. From 60 min onwards the labelling index remained nearly constant. Retransfusions performed 3 days after splenectomy revealed only one nearly constant decline of the labelling index (halving time on average 129 min). After sham‐splenectomy the pattern of disappearance was similar to the preoperative experiment. One hour after the end of retransfusion the labelling index had decreased by three‐quarters of the initial value in normal pigs and by only one‐third in the splenectomized ones. These results indicate that in the pig the total rate of recirculation is at least 4 times faster with the spleen in situ than without the spleen.
CELL PROLIFERATION IN THE ERYTHROID COMPARTMENT OF GUINEA‐PIG BONE MARROW: STUDIES WITH 3H‐THYMIDINE
Authors: Starling Mark R. , Rosse Cornelius
Published: May 2008

Single and multiple injections of 3H‐TdR have been used for measuring the rate of proliferation in morphologically defined cell populations of guinea‐pig bone marrow that are committed to erythroid differentiation. The conclusions are based on the analysis of absolute cell numbers in the maturational compartments, the labeling and mitotic indices, labeled mitotic curves, pulse and chase grain counts over dividing and interphase cells, and on the rate of labeling during multiple, repeated injections of 3H‐TdR. The average duration of S and the rate of cycling is similar in all maturational compartments of the erythron. The majority of cells progress to the next maturational compartment by the time they divide for the second time. All proerythroblasts and basophilic erythroblasts are in cycle. Polychromatic erythroblasts incapable of incorporating 3H‐TdR reach the orthochromatic population in the span of 5–6 hr. The orthochromatic population is renewed every 20–24 hr. The number of divisions between the proerythroblast and orthochromatic erythroblast does not exceed four and some cells may undergo only two divisions during the maturation pathway. Cell input from a progenitor cell population contributes to the maintenance of the erythron. The kinetic behavior of progenitor cells is similar to that of proerythroblasts. By the time of their second division, progenitor cells may reach either the proerythroblast or basophilic erythroblast compartments. The kinetic behavior of basophilic transitional cells corresponds to the predicted behavior of the erythroblast progenitor cell pool. Several of the conclusions are based on the assumption that grain count halving is the result of cell division. In view of the evidence discussed, this assumption in the present studies seems justified.
STUDY OF THE EFFECT OF HYDROXYUREA ON THE ERYTHROPOIETIN‐SENSITIVE CELLS
Authors: Nećs E. , Neuwirt J.
Published: May 2008

The response of polycythaemic mice to a standard dose of erythropoietin has been measured at various, time intervals after single or repeated injections of hydroxyurea. The results exclude S phase of the cell cycle as the period responsive to erythropoietin. They suggest the existence of feedback mechanisms within the cell cycle, operating at the G1‐S boundary and within the G1 phase.

Hydroxyurea given to polycythaemic mice at various time intervals after erythropoietin induced characteristic changes in the response. These changes can be explained if both gradual transit of differentiated cells into the DNA synthesis (S phase) and changes in amount of the erythropoietin sensitive cells caused by the feedback mechanisms operating in the cell cycle are considered.
CYTODYNAMICS IN THE THYMUS OF YOUNG ADULT MICE:
Authors: Cläesson Mogens Helweg , Hartmann Niels Rudolph
Published: May 2008

Cell proliferation and cell loss in the thymic blast cell population were studied in young adult mice by (1) stathmokinetic methods combined with an analysis of the PLMe‐curve after a pulse 3H‐TdR, and (2) nigrosin‐dye exclusion combined with 3H‐TdR‐autoradiography. It was calculated that about 17% of the blast cells do not progress into mitosis within the period of an average cell cycle. The dye exclusion studies indicated a rate of blast cell death of about 2–5 %/hr. The two methods of assessing blast cell loss (death) support each other very well. In spite of these findings scintillation countings on thymuses removed from 1 to 17 hr after 3H‐TdR injection showed fairly constant levels of thymic radioactivity. This suggests a very extensive reutilization of 3H‐labelled break‐down products from dying blast cells. The very sparse labelling of pyknotic thymocytes strongly suggests that thymic blast cells do not become pyknotic. The rate of small thymocyte production and disappearance was studied by pulse and repeated 3H‐TdR labelling techniques combined with dye exclusion studies and pyknotic counts. The data from the repeated labelling experiment were analysed by use of a model based on the assumption of first order kinetics of small viable, dead, and pyknotic thymocytes. The rate of cell production was estimated to 1–6 %/hr whereas the rates of cell loss due to disintegration, i.e. supravital stainability and nuclear pyknosis, were calculated to 0–02 %/hr and 0–0006 %/hr respectively. Cell loss due to disintegration was less than 2 % of the total loss of small thymocytes. It was concluded that pyknotic counts are a useless method of assessing the cell death in the population of thymic blast cells and small thymocytes. On the basis of a model for thymocyte proliferation, production and loss it is suggested that about 45 % of the small viable thymocytes re‐enter the generative cell pool, whereas about 55% disappear by emigration.
PERIODONTAL LIGAMENT CELL KINETICS FOLLOWING ORTHODONTIC TOOTH MOVEMENT
Authors: Yee J. A. , Kimmel D. B. , Jee W. S. S.
Published: May 2008

The population of periodontal ligament (PDL) fibroblasts examined in this study may include osteogenic progenitor cells. PDL fibroblast and osteoblast kinetics in the periodontal ligament of the rat were measured following orthodontic stimulation of bone formation. Both single and multiple injections of tritiated thymidine (3H‐TdR) were used. In single injection experiments, the peak percentage of PDL fibroblasts labeled with 3H‐TdR is 15% at 22 hr post‐stimulation. In multiple injection experiments, the total percentage of fibroblasts in the PDL which respond by synthesizing DNA is 50%. 3H‐TdR‐Iabeled osteoblasts appear at the same rate as, but with a time delay after, the labeled fibroblasts. Following stimulation, the most likely source of osteoblasts at the bone‐forming site is not only fibroblasts which make DNA, divide, then differentiate, but also fibroblasts which either are differentiated to osteoblasts without DNA synthesis and cell division, or are released from G2 block by the orthodontic stimulation.
A TECHNIQUE FOR DETERMINING THE PROPORTION OF THE CLONOGENIC CELLS IN S PHASE IN EMT6 CELL CULTURES AND TUMORS
Authors: Rockwell Sara , Frindel Emilia , Tubiana Maurice
Published: May 2008

The survival of cultured EMT6 cells was examined after treatment with hydroxyurea (HU) or high specific activity tritiated thymidine (3H‐TdR). The concentrations of the agents, duration of exposure to the agents, and post‐exposure treatment of the cultures were found to influence the cell survival; the effects of these factors are reported. Conditions were defined under which the proportions of cells killed by HU and by 3H‐TdR were the same and were also the same as the proportion of labeled cells seen on autoradiographs of cultures labeled with small doses of 3H‐TdR. Under these conditions, either 3H‐TdR or HU could be used to determine the proportion of the clonogenic cells in S phase.

Single cell suspensions prepared from solid EMT6 tumors were treated in vitro with HU or 3H‐TdR, using the conditions found optimal for each agent with cultured cells. The proportion of the tumor cells killed by treatment with HU in vitro was the same as the proportion killed by HU in vivo and as the proportion labeled by 3H‐TdR in vivo, and incubation of tumor cell suspensions with HU in vitro appeared to provide a valid measurement of the proportion of clonogenic tumor cells in S phase. Incubation of tumor cell suspensions with 3H‐TdR in vitro proved difficult to perform and the results were relatively unreliable because of severe problems with reutilization of 3H‐TdR during the incubation for colony formation.
EFFECT OF METHOTREXATE ON THE CELL CYCLE OF L1210 LEUKEMIA
Authors: GONCHAROVA S. A. , FRANKFURT O. S.
Published: May 2008

The influence of methotrexate (MTX) on the proliferative activity of cells in different phases of cell cycle has been studied. MTX (5 mg/kg) was injected i.p. 3 days after the inoculation of 5 × 106 leukemia cells into F1 (DBA × C57 BL) mice. It was shown that MTX causes degeneration of cells, being in G1‐ as well as in S‐phase at the time of drug injection. Incorporation of 3H‐TdR was suppressed for a period ranging from 2 to 12 hr after MTX administration, which is demonstrated by the decrease in the number of grains per cell. The number of cells labeled after 3H‐TdR injection was also sharply decreased during this period. For a period of 3 until 15 hr after MTX administration the mitotic index decreased significantly as a result of inhibition of DNA synthesis. The blocking of the G1‐S transition was evident during 4 hr after MTX. Thereafter the G1‐S transition proceeds at a rate which is practically equal to that for nontreated controls. MTX did not inhibit transition to mitosis of cells being in G2‐phase and in a very late S‐phase at the time of drug injection.

The sensitivity of G1‐cells to the cytocidal effect of MTX shows that for L1210 leukemia cells MTX can be classified as a cycle‐specific drug killing both G1 and S‐cells rather than S‐phase specific agent with self‐limitation.
CELL VOLUME GROWTH AFTER CELL CYCLE BLOCK WITH CHEMOTHERAPEUTIC AGENTS
Authors: Ross Dennis W.
Published: May 2008

The effects of various chemotherapeutic agents on the volume of Chinese hamster V79 fibroblasts and murine lymphoma L5178Y cells were studied by electronic volume spectroscopy. Cells arrested in the division cycle by a chemotherapeutic block continued to grow in volume resulting in abnormally large cells unable to reduce their volume by cell division. This was observed in cells treated with colcemid, vinblastine, excess thymidine, hydroxyurea, ARA‐C, 5‐fluorouracil, actinomycin‐D and bleomycin, but not with puromycin or cycloheximide. Increase in cell volume of blocked cells was correlated with a decrease in cell survival as measured by clonogenic ability. The results suggest the possibility of volume spectroscopy for a rapid in vitro test to determine tumor sensitivity to chemotherapeutic agents and the in vivo monitoring of response to chemotherapy. Mechanisms for increased cell kill by a second agent acting selectively on enlarged cells are considered.
KINETICS OF PHYTOHEMAGGLUTININ STIMULATED LYMPHOCYTES IN CHRONIC LYMPHOCYTIC LEUKEMIA
Authors: JAKSIC B. , PAGLIARDI G. L. , PEGORARO L.
Published: May 2008

The DNA synthesis pattern and several kinetic parameters of in vitro PHA stimulated normal and CLL lymphocytes were determined. The DNA synthesis peak of CLL lymphocytes occurred 2–3 days later than that of normal lymphocytes. The generation time, estimated by the labeled mitoses method, was found to be 28 hr and 20 hr for CLL and normal lymphocytes respectively. This difference was mainly due to longer S and Gt periods. It was also shown that both CLL and normal lymphocytes divide several times. These data were confirmed by the chromatid labeling pattern and by the halving of the grains and the double labeling techniques. By combining continuous and pulse labeling the growth fraction of CLL lymphocytes was found to be progressively increasing, because of the recruitment of new cells in cycle, from the third day of culture. Therefore the delayed peak of DNA synthesis of CLL lymphocytes was caused by a longer cell cycle and by a longer pre‐replicative phase.
EFFECT OF VARIOUS DOSES OF ESTROGEN TO BALB/cCrgl NEONATAL FEMALE MICE ON MAMMARY GROWTH AND BRANCHING AT 5 WEEKS OF AGE
Authors: Warner M. R.
Published: May 2008

High doses of 17β‐estradiol given newborn mice the first 5 days of life had no effect on mammary growth at 3 weeks of age whereas glands measured at 5 weeks of age displayed marked dose‐dependent differences in area and branching.

The number of duct branches increased significantly as the estrogen dose was raised from the 25 μg threshold to 35 or to 70 μg. Ratios between area and branching remained constant under all experimental conditions.

Regional, dose‐dependent, differences in gland‐pair response were also observed at 5 weeks. Mammary gland pairs differed significantly in several growth parameters. The third gland pair was smaller in area and had fewer branches, but the opposite was true of the second and fourth gland pairs. Systemic injection of high doses of 17β‐estradiol into neonates reduced differences in growth parameters between gland pairs.
ANALYSIS OF CELL CYCLE COMPARTMENTS OF HEPATOCYTES AFTER PARTIAL HEPATECTOMY
Authors: Mrabes Hartmut , Wirsching Rainer , Tuczek Heinz‐Volker , Iseler Gerd
Published: May 2008

An analysis of cell kinetic parameters as a function of intralobular localization of hepatocytes was performed using autoradiographic methods to obtain a basis for a quantitative description of cell cycle compartments after partial hepatectomy.

The influx into the S compartment revealed a maximum in a lobular zone not immediately adjacent to the portal tract, with a decrease towards the perivenous and periportal area of the lobule. The maximum influx was found in the intermediate zone at 34 hr and a lower one in the perivenous parts of the lobule at 40 hr. The influx pattern at 56 hr was similar to the situation at 18 hr.

The fraction of labelled mitoses in the whole liver and in subunits of the lobule disclosed a constant duration of S whereas the duration of G2+ M was prolonged from the periportal to the perivenous zone.

A graphical model of kinetic events after partial hepatectomy is proposed, which describes the sizes of the various cell cycle compartments; the model successfully predicted the results of a continuous labelling experiment.
CELL KINETICS OF A CHONDROSARCOMA
Authors: Dawson Anne , Kember N. F.
Published: May 2008

The cell kinetics of the transplantable DC‐II mouse chondrosarcoma have been studied by the pulse labelled mitoses method. The analysis gave the following estimates for the phases of the cell cycle: G, 10‐5 hr; S, 9‐5 hr; G2, 4 hr with an intermitotic time of 23‐5 hr. Consideration of the overall growth of the tumour indicated that the growth fraction and cell loss factor both had values of about 0–5. The results are compared with cell kinetic data from sarcomas and other cartilage tissues.
REGENERATIVE PROLIFERATION OF MOUSE EPIDERMAL CELLS FOLLOWING ADHESIVE TAPE STRIPPING
Authors: Clausen O. P. F. , Lindmo T.
Published: May 2008

The proliferating cells of mouse epidermis (basal cells) can be separated from the non‐proliferating cells (differentiating cells) (Laerum, 1969) and brought into a mono‐disperse suspension. This makes it possible to determine the cell cycle distributions (e.g. the relative number of cells in the G^ S and (G2+ 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 Gj 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.
RELATIONSHIP OF NUTRITIONAL FACTORS TO IN VITRO TUMOR CELL GROWTH AND CYTOTOXICITY PRODUCED BY CYTOSINE ARABINOSIDE
Authors: Momparler Richard L. , Goodman Joel
Published: May 2008

The in vitro relationship between nutritional factors, proliferative status of tumor cells, and the cytotoxic action of cytosine arabinoside (ara‐C) was investigated. The reduction in the concentration of only one essential amino acid, L‐isoleucine, in the growth medium of A(T1)Cl‐3 hamster fibrosarcoma cells decreased DNA synthesis in this cell population and slowed the rate of progression of G1 phase cells into S phase of the cell cycle. The complete omission of isoleucine from the growth medium blocked the progression of G1 phase cells into S phase and prevented the cytotoxic action of ara‐C. The addition of isoleucine to the isoleucine‐deprived cells permitted these cells to enter the S phase and restored their sensitivity to the cytotoxic action of ara‐C. When G1 phase cells were placed in a medium containing reduced levels of all the amino acids and vitamins there was a prolongation of the G1 phase. Since medium with low levels of amino acids produced a delay in the entry of G1 phase cells into the S phase, the time interval in which these cells were most sensitive to the cytotoxic action of ara‐C was different for G1 phase cells placed in medium with adequate levels of all the amino acids. These in vitro data indicate that nutritional factors can markedly effect the proliferation of tumor cells and the cytotoxic action of ara‐C.
SPECIFIC CHALONE INHIBITION OF THE REGENERATION OF THE JB‐1 ASCITES TUMOUR STUDIED BY FLOW MICROFLUOROMETRY
Authors: Bichel P. , Barfod N. M.
Published: May 2008

The variation in the DNA distribution in the JB‐1 and the Lla2 ascites tumour was investigated by means of flow microfluorometry (FMF) in the plateau stage and during the initiation of the regeneratave growth induced by percutaneous aspiration. The study showed that a considerable influx of cells with G1 DNA content into the S phase occurred in both tumours about 10 hr after aspiration.

In the JB‐1 tumour, these initial regenerative changes could be reversibly blocked by injections of cell‐free plateau JB‐1 ascitic fluid or an ultrafiltrate of this ascites. In contrast to these observations no delay in the regenerative changes was observed in the Lla2 tumour after treatment with JB‐1 ascites or the ultrafiltrate.

The study supports the assumption of a specific growth regulation of the JB‐1 ascites tumour and emphasizes the suitability of FMF analyses in cell‐kinetic studies in which short‐term fluctuations take place in the distribution of cells with different DNA content.
EFFECTS OF PRE‐IRRADIATION ON ISOGENEIC AND SEMI‐ISOGENEIC CFU GROWTH: A STUDY ON GENETIC RESISTANCE
Authors: Buurman W. A. , Bruggen Ivonne van
Published: May 2008

The genetic resistance to a parental bone marrow transplant as demonstrated, when transplantation was performed early after irradiation, failed to occur if the interval between irradiation and transplantation was increased to 4 days. A similar radiation induced weakening of genetic resistance to a parental bone marrow graft in spleen and bone marrow could be demonstrated in mice, which had been irradiated with a sublethal dose at 7 days prior to the lethal irradiation and transplantation. The pre‐irradiation of the recipient with a sublethal dose induced an enhancement of the growth in spleen and bone marrow of isogeneic transplanted CFU. The pre‐irradiation of a single tibia also resulted in a significant weakening of the resistance in the spleen. The experiments with partial body pre‐irradiation suggested a local effect of the pre‐irradiation, but it could be shown that the enhanced CFU growth is not caused by an enhanced seeding of CFU in pre‐irradiated bone marrow. The role of microenvironment in the phenomenon of genetic resistance is discussed.
SOME PROPERTIES OF A ‘G0’‐MODEL OF THE CELL CYCLE
Authors: Maertelaer V. de , Galand P.
Published: May 2008

The two‐phase (G and C phases) model first proposed by Burns & Tannock (1970) to describe the cell cycle kinetics has the major advantage of requiring only two parameters for a complete description of the kinetic behaviour of populations that are in a steady‐state, or that grow exponentially (with no cell loss from the population).

Steady‐state populations were examined in paper I of this series. Exponential populations with no cell loss are investigated here. The model assumes two basic kinetic states—a ‘C’phase which includes S, G2, M and perhaps part of G1, and a ‘G’phase which cells enter after completing the C‐phase and from which either are lost or return to C‐phase randomly. The model assumes that transit time through C‐phase is constant for all cells in the population. An original method is described which allows the determination of two independent parameters of the model from the experimental ‘fraction of labelled mitoses’(FLM) curve. From those two parameters, the ratio of G‐cells among the total number of cells (NG/N) has been calculated for each cell population studied. The range of the NG/N values thus obtained is fairly restricted, and the mean NG/N value for exponential growths is not statistically different from that found in steady‐states considering in that case the only sub‐population of cycling cells (i.e. the cells that will undergo a further mitosis).
EFFECTS OF BLEOMYCIN ON THE EPIDERMAL CONTENT OF GROWTH‐REGULATORY SUBSTANCES (CHALONES)
Authors: Iversen O. H. , Clausen O. P. F. , Elgjo K. , Iversen Ulla M. , Rohrbach R.
Published: May 2008

Hairless male mice were given 2 mg Bleomycin i.p. on two successive days. At different time intervals from 1 to 10 days after the last Bleomycin injection, groups of animals were killed and water extracts of homogenized skin were made.

These extracts, supposed to contain the epidermal G1 and G2 chalones, were injected into female hairless mice, and their growth inhibitory potency determined by two methods. 5 mg of lyophilized crude skin extract were injected i.p. together with Colcemid, and the animals killed 4 hr later. The number of Colcemid‐arrested mitoses was determined, and was considered to be a measure of the G2 inhibitor present in the skin extracts. 10 mg of the same extracts were injected i.p., and these animals also got 3H‐TdR i.p. 12 hr later, and were killed after a subsequent 30 min. The epidermal LI was determined, and was considered to be a measure of the epidermal G1 factor in the skin extracts. The results obtained were compared to the effect of Bleomycin alone and to the effects of skin extracts from non‐Bleomycin‐treated animals.

The results show that Bleomycin provoked slight alterations in the growth‐inhibitory potency of the G1 chalone, whereas significant effects were seen in the G2 chalone. There was an increased amount of growth‐inhibiting factors on days 2 and 3, and on days 8–10.

The results are discussed and it is concluded that the most probable hypothesis is that Bleomycin, in addition to its known inhibitory effect on epidermal cell proliferation, exerts growth inhibition by accumulation of cells with high growth inhibitory potency. An initial, additional direct effect of Bleomycin on the chalone system cannot be excluded.
THE EFFECT OF A SINGLE INJECTION OF HYDROXYUREA ON CELL POPULATION KINETICS IN THE SMALL BOWEL MUCOSA OF THE RAT
Authors: Al‐Dewachi H.S. , Wright N. A. , Appleton D. R. , Watson A. J.
Published: May 2008

The effect of a single injection of hydroxyurea (HU) on cell population kinetics in the jejunal crypt of the rat was studied using autoradiography with tritiated thymidine and metaphase arrest with vincristine. HU appeared to act selectively on cells in the S phase producing inhibition of DNA synthesis and cell death. The deficit in proliferating cells was made good by a decrease in cell cycle time and an increase in growth fraction. Particular attention was paid to the basal, slowly cycling (and possibly clonogenic) crypt cells; early in the recovery sequence an increase in cell production rate was found in the base of the crypt.

It is proposed that basal crypt cells, having survived cycle‐specific insult because of long cell cycle times, proceed to repopulate the depleted proliferative compartment.
THE EFFECTS OF RED BLOOD CELL EXTRACTS ON THE PROLIFERATION OF ERYTHROCYTE PRECURSOR CELLS, IN VIVO
Authors: Lord B. I. , Shah G. P. , Lajtha L. G.
Published: May 2008

Saline incubation extracts of mature erythrocytes were assayed in vivo by a variety of techniques in order to study their ability to modify the proliferation of maturing erythroid cells. Using comparable extracts from granulocytes and lymphocytes, the specificity of the effect of the red cell extract for erythroid cells was confirmed by measurement of autoradiographic labelling indices, radio‐iron incorporation and spleen colony growth. The erythroid cells were found to be very sensitive to the effects of the extract, as little as 10 μg per mouse producing a maximum effect on iron incorporation. It was found that the extract does not block erythroid cell proliferation completely but simply lengthens the cell cycle, mainly by increasing the G1 phase of the cycle. There was no effect on the committed erythroid precursor cells. The in vivo activity, specificity and non‐toxicity to the cells, together with the cells' sensitivity to red cell extract suggest, therefore, that this inhibitor may play a physiological role in the control of red cell production.
PROPERTIES OF THE H‐4‐II‐E TUMOR CELL SYSTEM
Authors: Kovacs C. J. , Evans M. J. , Hopkins H. A.
Published: May 2008

The growth and cell proliferation characteristics of the H‐4‐II‐E cell line, giving rise to hepatoma H‐4‐II‐E when inoculated into male ACI rats, were studied in vitro. Following seedling of 2 × 103 cells into culture dishes, exponential cell growth occurs in cultures fed both at 24 hr and 48 hr intervals with a population doubling time of 18.4 hr. Plateau phase growth conditions are established on day 7 and day 5 for cultures fed at 24 hr and 48 hr intervals respectively. Both the plateau phase cell density and the maintenance of plateau phase appear dependent on the frequency of feeding. For cultures fed daily, the transition from exponential growth to plateau phase results from both a reduction in the number of proliferating cells (99% v. 35%) as well as an elongation of the cell cycle (17.7 hr v. 128.4 hr). The cell proliferation characteristics of the culture are further discussed in reference to both cell growth and feeding schedules of other cell lines.
INCREASED CELL PROLIFERATION WITH PERSISTENCE OF CIRCADIAN RHYTHMS IN HAMSTER CHEEK POUCH NEOPLASMS
Authors: Izquierdo J. N.
Published: May 2008

Squamous cell neoplasms induced by repeated topical application of 7,12‐dimethyl‐benz(a)anthracene in Syrian hamster cheek pouch exhibited circadian rhythms of DNA synthesis and mitotic activity. Fluctuations in the fractions of cells in mitosis and DNA synthesis observed in the tumors were approximately in phase with the circadian rhythms from normal precursor epithelium, indicating that some degree of host physiologic modulation persists during neoplastic growth. The labeling (thymidine‐3H) and mitotic indices of neoplasms were considerably higher than normal throughout the 24 hr period. The duration of the neoplastic S phase—measured from the PLM curve—was 30% shorter than normal; G2 did not show detectable variation. The data demonstrated that chemically induced squamous cell neoplasms had markedly increased rates of cell production. It is postulated that applications of a carcinogen upon a cell‐renewing population generate a multicompartmental cytokinetic imbalance in which: (1) a higher proportion of G0 cells is stimulated to enter the cycle; (2) the duration of the cell cycle is shortened; (3) the regulatory mechanisms fail to stimulate an accelerated rate of differentiation to compensate for the overproduction of cells; and (4) the state of proliferative hyperactivity becomes stable. An oncogenic cytokinetic mechanism based solely on a persistent decrease in cell loss (differentiation) is ruled out by the present investigation, at least for squamous cell neoplasms.
CELL CYCLE TIME DETERMINATIONS BASED ON LIQUID SCINTILLATION COUNTING OF 3H‐TdR LABELED MITOTIC CELLS
Authors: Barranco S. C. , Haenelt B. R. , Bolton W. E.
Published: May 2008

Following a 10 min pulse labeling with 3H‐TdR, flasks of asynchronous monolayer cultures of Chinese hamster ovary cells were subjected to mitotic selection at 2 hr intervals. The mitotic index of the selected populations was always greater than 90%. Counts per min per cell obtained by liquid scintillation counting were plotted versus time after the pulse label. Comparisons were made between cycle times obtained by the mitotic‐scintillation counting method and by the standard per cent labeled mitosis technique. The resulting curves were used for calculations of the cell cycle times and the lengths of G1, S, G2 and M phases of the cell cycle. There was less than 2% difference in the cell cycle times obtained using the scintillation method as compared to times calculated from autoradiographic data obtained from individual petri dishes.

The mitotic‐scintillation counting technique is simple, accurate and rapid and allows the calculation of the cell kinetics parameters within 1 hr of the end of the experiment.
THE IN VITRO DIFFERENTIATION OF DENSITY SUB‐POPULATIONS OF COLONY‐FORMING CELLS UNDER THE INFLUENCE OF DIFFERENT TYPES OF COLONY‐STIMULATING FACTOR
Authors: Byrne P. , Heit W. , Kubanek B.
Published: May 2008

The in vitro proliferation and differentiation of myeloid progenitor cells (CFU‐c) in agar culture from CBA/Ca mouse bone marrow cells was studied. Density sub‐populations of marrow cells were obtained by equilibrium centrifugation in continuous albumin density gradients. The formation of colonies of granulocytes and/or macrophages was studied under the influence of three types of colony‐stimulating factor (CSF) from mouse lung conditioned medium CSFMLCM), post‐endotoxin mouse serum (CSFES) and from human urine (CSFHu). The effect of the sulphydryl reagent mercaptoethanol on colony development was also examined. The density distribution of CFU‐c was dependent on the type of CSF. Functional heterogeneity was found among CFU‐c with partial discrimination between progenitor cells forming pure granulocytic colonies and those forming pure macro‐phage colonies. Mercaptoethanol increased colony incidence but had no apparent effect on colony morphology or the density distribution of CFU‐c.
EFFECTS OF UTERINE DISTENSION AND OESTRADIOL ON CELL KINETICS IN THE ENDOMETRIAL EPITHELIUM OF OVARIECTOMIZED RATS
Authors: Leroy F. , Hoeck J. Van , Bogaert C.
Published: May 2008

Cell kinetics in the uterine epithelium of ovariectomized rats were studied after uterine distension and/or an oestradiol injection, by cumulative 3H‐TdR labelling and percentage of labelled mitoses (PLM). With both methods it was found that distension shortens the total cell cycle at the expense of G1 more than does oestradiol. Both treatments act in a cumulative manner since the greatest reduction in Tc is observed after distension plus oestradiol. PLM curves showed that distension and/or oestradiol induce a 30% reduction in S phase duration. The evolution of percentages of labelled cells and colchicine‐blocked mitoses after these treatments confirms their additive effects and indicates that the mitogenic action of oestradiol is delayed compared to that of distension. It is suggested that these factors stimulate epithelial cell division in the uterus through partly different metabolic channels.