bluuebunny/crossref_metadata_2025 huggingface dataset:
ERYTHROPOIETIC CELL POPULATION CHANGES DURING THE HEPATIC PHASE OF ERYTHROPOIESIS IN THE FOETAL MOUSE
Authors: Paul J. , Conkle D. , Freshney R. I.
Published: May 2008

Estimates have been made of the absolute numbers of hepatogenic erythropoietic cells from 12.5 days post fertilization onwards in the mouse. All stages of maturation up to reticulocytes are present in the earliest samples but the least mature cells (proerythroblasts and basophilic erythroblasts) predominate; more mature cells (orthochromatic erythroblasts, reticulocytes and erythrocytes) predominate later in development. The number of hepatogenic haemoglobinized cells increases exponentially with a population doubling time of about 8 hr until about 15.5 days post fertilization. There is then a sharp transition and the doubling time lengthens to about 2 days. The immature cells formed during the rapid phase of increase are poorly haemoglobinized; hence the increase in haemoglobin lags behind that of cells. Calculations of the rates of formation of hepatogenic haemoglobinized cells and haemoglobin per standard number of liver cells show maxima between 15 and 16 days; these findings are in accord with direct observations of rates of haemoglobin synthesis in cultured mouse foetal livers made previously.
BONE MARROW RESTORATION AFTER LOCALIZED DEPLETION
Authors: Maloney Mary A. , Patt Harvey M.
Published: May 2008

Studies have been made of marrow restoration after localized depletion of the rabbit femur by dextran perfusion. Restoration was shown to involve an initial period of reorganization which blends with a more prolonged period of hemic cell repopulation. Cellularity returned to normal levels by 35 days, the recovery of myeloid cells being somewhat more rapid than that of the erythroid elements. In either case, the evolution of immature hemic cells was soon followed by the appearance of more mature forms even at the earliest stages of marrow repopulation. 3H‐TdR uptake per cell increased rapidly to a level approximately twice normal after the first week. The augmented incorporation of thymidine, revealed by scintillation spectrometry and confirmed upon autoradiography, was shown to be due to an increase in DNA synthesis rate as well as in the fraction of participating cells. It is suggested that the enhanced cell production is brought about by a decrease in the proliferative cell cycle and an increase in the growth fraction. The origin of the repopulating cells remains a moot point. Cell migration from the epiphyseal marrow is apparently not involved. Irrespective of the source of stem‐type cells, the stimulus for regeneration appears to be locally determined.
PROLIFERATION KINETICS OF AN EXPERIMENTAL ASCITES TUMOUR OF THE MOUSE
Authors: Frindel E. , Valleron A. J. , Vassort F. , Tubiana M.
Published: May 2008

The cell cycles of an experimental ascitic tumour of the C3H mouse (NCTC 2472) were determined at various times after the intraperitoneal injection of 106 cells.

It was found that, contrary to results in solid NCTC 2472 tumours, obtained with the same NCTC cells, the duration of the cell cycle and its phases lengthened with the age of the tumour while the growth fraction remained relatively constant. G1 was the first phase to lengthen, while later Ts and TG2 increased also.

The amount of DNA per cell was determined by cytospectrophotometry. This method provides data on the evolution during growth of the relative number of cells in each phase of the cell cycle.
ON THE RESTING PERIODS IN THE CELL LIFE CYCLE*
Authors: Epifanova Olga I , Terskikh V. V.
Published: May 2008

The review is concerned with the transition of cells into a specific physiological state—the resting period—in which they may stay for an indefinite time interval without undergoing division or differentiation but retaining both of these potentials. When stimulated such cells may enter into mitotic cycle, divide and differentiate.

No direct correlation between the onset of the differentiated state and the transition of cells through the mitotic cycle has been established. It cannot be excluded that sometimes cells may differentiate directly from the resting period. However, there is a large body of evidence that the entry of cells into mitotic cycle is a necessary prerequisite for subsequent differentiation. The susceptibility of cells to differentiative stimuli is retained during the mitotic cycle. The completion of mitosis itself does not imply that a cell will undergo differentiation; in the absence of adequate stimulus it may pass again into a resting period.

According to what is known at present it is suggested that cells may pass into a true resting stage not only after completing mitosis but also after doubling their DNA content. It is also conceivable that a cell may pass into a resting period at different stages of its life cycle. The essential feature of the cell life cycle is the alternation of resting periods and periods of active proliferation. This general principle of organization provides conditions necessary for population‐size control, cell differentiation, interaction of a given population with other systems, and the reactions of cells to a changing environment.
THYROID PROLIFERATIVE POTENTIAL AS A FUNCTION OF AGE
Authors: Sheline Glenn E.
Published: May 2008

The effect of a goitrogenic stimulus on thyroid weight and thyroid cell 3HTdR labeling of Sprague‐Dawley rats varying from 2 to 40 weeks of age was determined. Propylthiouracil ad libitum in drinking water produced a spurt in follicle cell labeling index and thyroid weight evident after 24 hr for all age groups. The increase in labeling index reached a peak at 5–7 days and then decreased to a level a few times greater than that of the normal unstimulated thyroid. The tritiated thymidine labeling index for thyroid follicle cells and the effect of PTU thereon was determined for August male rats of 3 days to 12 weeks of age. In the older rats, the follicle cell labeling index rose to 5–6% after 4–5 days of PTU treatment and then slowly fell to about 1%, For the unstimulated control rat of comparable age, the labeling index was about 0.1%. At all ages the thyroid showed a rapid response to PTU. Examination of the time sequence of mitotic labeling showed that the DNA synthesis period was 7.5 hr for normal 2‐week‐old rats and for 10–12‐week‐old rats that had received PTU for 4 days. There was no second wave of labeled mitoses in either group during the 48‐hr interval studied. From the curve of thyroid weight vs time on PTU and from the labeled mitoses curve, inferences regarding the minimum fraction of proliferating follicle cells in the stimulated ‘adult’rat thyroid were made.
ON THE QUESTION OF LONG‐LIVED RNA IN MAMMALS
Authors: Menzies R. A. , Press G. D. , Gold P. H. , Hendley D. D. , Strehler B. L.
Published: May 2008

RNA was isolated from various mouse tissues 126 days after the injection of 14C‐uridine and 37 days after the injection of 3H‐uridine. Calculations based on a small but definite residual amount of 14C‐labeled RNA suggest the existence of an RNA with a half‐life in excess of 10 days. Independent calculations based on the ratio of 3H and 14C dpm in chromatographically isolated UMP suggest a minimum half‐life of about 30 days.
AUTORADIOGRAPHIC STUDIES OF EOSINOPHIL KINETICS: EFFECTS OF CORTISOL*
Authors: Andersen Vagn , Bro‐Rasmussen Frede , Hougaard Kjeld
Published: May 2008

The effect of cortisol administration upon the labelling of blood eosinophils was studied in rats given a single injection of 3H‐thymidine. One dose of cortisol did not change the subsequent course of labelling of eosinophils, whereas steroid treatment for 3 days resulted in a delay of the most heavily labelled class. The results seem to indicate that cortisol causes a reversible sequestration of blood eosinophils; and that long‐term steroid administration may delay the release of eosinophils from the bone marrow into the blood.
MEASUREMENT OF THE DURATION OF DNA SYNTHESIS IN ERYTHROID CELLS OF THE BONE MARROW USING A DOUBLE LABELLING AUTORADIOGRAPHIC TECHNIQUE DESIGNED SPECIFICALLY FOR USE WITH HAEMOPOIETIC TISSUES
Authors: Lord B. I.
Published: May 2008

This paper describes a double labelling autoradiographic technique for use with haemopoietic tissues. In involves two photographic emulsions separated by a thin piece of mica on which the cells have been smeared. In this way the autoradiographic grains due to tritium and carbon‐14 appear above and below the cells respectively.

Applying the method to bone marrow normoblasts of young rats, the average duration of DNA synthesis (ts) for the pro‐ and early normoblasts taken together is found to be 5.1 hr and the mean cell cycle time (tc) to be 8.2 hr. For the intermediate normoblasts, the corresponding figures are 6.3 hr and 15.7 hr. Average values for all dividing normoblasts in the bone marrow are 5.8 hr and 12.8 hr respectively for ts and tc. The average duration of mitosis is 32 min.
AN EXPERIMENTAL INVESTIGATION OF THE DIVISION PROBABILITY MODEL FOR CELL GROWTH
Authors: Pujara Chandrakant M. , Whitmore Gordon F.
Published: May 2008

Mouse L cells grown in the presence of BUdR for long periods of time exhibit exponential growth with doubling times which are appreciably longer than the doubling times or generation times of populations not exposed to the drug. The experiments described here indicate that this growth and these long doubling times are not the result of selecting mutant cells resistant to BUdR nor with long generation times. Instead the experimental evidence presented suggests that the growth kinetics can be explained on the basis of the P model. Using this model together with experimental data has made it possible to obtain three independent determinations of the P value for cell populations growing in the presence of various concentrations of BUdR. Within experimental error the three values of P determined for each BUdR concentration are in agreement with one another. Therefore, it is concluded that the division probability model provides an adequate description of the growth properties of L60T cells growing in the presence of BUdR.
A COMPARATIVE STUDY OF THE REPOPULATING POTENTIAL OF GRAFTS FROM VARIOUS HAEMOPOIETIC SOURCES: CFU REPOPULATION
Authors: Schofield R.
Published: May 2008

The growth rate of the CFU populations in spleens and femora has been studied in irradiated mice injected with cell suspensions, containing equivalent number of CFU, from various sources. The doubling times are shown to be dependent upon the source of the cells. Grafts of bone marrow, spleen and foetal liver cells produced doubling times in the spleen of approximately 25, 19 and 16 hr respectively. Grafts of marrow‐derived and spleen‐derived spleen colony cells both gave rise to CFU doubling times lower than those of the corresponding primary grafts (approx. 33 and 26 hr respectively in the spleen). In the case of both bone marrow and spleen grafts the CFU population growth was shown to be independent of the size of the graft. A hypothesis is advanced which invokes at least a dual population of CFU, having different doubling times, different seeding capacities in the haemopoietic tissues following i.v. injection and present in different proportions in the various haemopoietic tissues.
SELECTIVE INHIBITION OF EMBRYONIC DEOXYRIBONUCLEIC ACID SYNTHESIS BY VINBLASTINE
Authors: Williams J. P. G.
Published: May 2008

Vinblastine inhibits the synthesis of DNA in mouse fetuses in utero, the incorporation of tritiated thymidine into the gut of the parent is, however, not altered. This selective effect, although found with other spindle inhibitors, is not due to the mitotic arresting property of the drug.
EFFECTS OF IRRADIATION ON THE GENERATIVE CYCLE OF THE ESTROGEN STIMULATED VAGINAL EPITHELIUM
Authors: Ladinsky J. L. , Gruchow H. W.
Published: May 2008

The effects of irradiation (300, 500 and 1500 rads) on mitosis and DNA synthesis in the estrogen primed vaginal epithelium have been studied. Dose‐effect relations and the time sequence of effects on the two processes were investigated. The technique of tritiated thymidine labeling of DNA with autoradiography was used, in conjunction with the mitotic count, to study alterations in the generative cycle. Prior to irradiation, ovariectomized female rats were treated daily with diethylstilbestrol for a period of 2 weeks to create a steady state in the vaginal cell population.

It was observed that:

Within 1 hr following ionizing radiation, mitotic figures disappear from the population and reappear at a time that is dose dependent. Those cells that have begun mitosis at the time of irradiation were able to complete that phase but no cells which were in G2 were able to begin mitosis. Therefore, a G2 block occurs within 1 hr post‐irradiation.

Radiation reduces the rate of DNA synthesis thus prolonging the S phase. There is no evidence of a radiation‐induced G1 to S block in this system.

Based on these observations, it was further hypothesized that:

Cells in G1 at the time of irradiation are relatively insensitive and continue to progress through the generative cycle at a rate primarily determined by the level of estrogen stimulation.

Radiation may interfere with the estrogen priming mechanism in this hormonedependent system thereby reducing the effective level of estrogen stimulation. This is seen in the behavior of cells which were in G1 at the time of irradiation. The extent of the blockage of estrogen increases with radiation dose and after 1500 rads, estrogen stimulation is essentially at castrate level.
ERYTHROCYTIC CHALONE, A TISSUE‐SPECIFIC INHIBITOR OF CELL PROLIFERATION IN THE ERYTHRON
Authors: Kivilaakso E. , Rytömaa T.
Published: May 2008

Control of the rate of cellular proliferation in the erythron seems to be mediated by a tissue‐specific mitotic inhibitor, termed the erythrocytic chalone. the function of this substance seems to be to prevent excessive proliferation of the erythrocyte precursor cells by means of a negative feedback and in terms of peripheral cell numbers.

The erythrocytic chalone is present in mature erythrocytes, from which it can be extracted by incubation in a chemically defined medium. It is also present in fresh normal serum and it is possible that in physiological conditions the factor is continuously liberated from mature erythrocytes into the surrounding plasma.

In the rat, in an artificially induced polycythaemia the concentration of the chalone in the serum is increased and this increment appears to be the sole cause of the enhanced inhibitory action of polycythaemic serum on the proliferation of the bone marrow cells in vitro.

The mode of action of the erythrocytic chalone seems to be to prevent the erythrocyte precursor cells from entering the generative cell cycle; the chalone thus regulates the production of erythrocytes by changing the ‘proliferation efficiency’ in the erythron.

So far, nothing is known about the chemical nature of the erythrocytic chalone. However, in gel filtration it is eluted in the same zone as the granulocytic chalone, its molecular weight thus being about 2000‐4000.
CELL PROLIFERATION DURING the COURSE of IMMUNOLOGICAL REJECTION of EHRLICH ASCITES TUMOUR CELLS
Authors: Janik Przemyslaw
Published: May 2008

Ehrlich ascites tumours were transplanted from their normal hosts (mice) into rats, and studies made of the timing of cell cycle 120‐170 hr after transplantation, when tumour regression was under way. There was no significant change in the duration of the cell cycle. Some increase was found in the average and spread of G2 durations, largely compensated by a decrease in S duration. When taken together with previously published work the results suggest that the immunological pressure of transplantation into a heterologous host prolongs the G2 period.
KINETICS OF THE INNER ENAMEL EPITHELIUM IN THE ADULT RAT INCISOR
Authors: Zajicek Gershom , Bar‐Lev Moshe
Published: May 2008

Rats were injected with tritiated thymidine and sacrificed at various time intervals up to 24 hr. the extracted incisors were decalcified, cut sagittally, dipped into liquid emulsion exposed for 14 days, developed and stained. the counting consisted of an exact mapping and numbering of the cells.

The inner enamel epithelium consists of two compartments: proliferative and mature cells. the first may be further subdivided into blasts and metablasts. Each dividing blast yields one blast and one metablast. the metablasts continue to divide further, at least once, yielding again two metablasts.

The kinetic parameters of this population are: generation time 22 hr, synthesis time 4.5 hr, mitotic time 30 min, G2 time 2 hr and G1 time 15 hr. the daily cell production of the proliferative compartment equals its size.
GROWTH HORMONE AND CARTILAGE CELL DIVISION IN HYPOPHYSECTOMIZED RATS
Authors: Kember N. F.
Published: May 2008

The effects of growth hormone on cell division in the growth cartilage of normal and hypophysectomized rats have been studied by autoradiography with tritiated thymidine. Following hypophysectomy the percentage labelling fell to 1.5‐2%, about one fifth of that found in normal animals. Following injection of 100‐1600 μg of bovine growth hormone, the percentage labelling increased after a delay of 8‐16 hr, the delay, the rate of rise and the maximum reached being dose dependent. Single or repeated doses of growth hormone produced no significant change in normal young rats.
GRANULOCYTE DYNAMICS AND THE QUESTION OF INEFFECTIVE GRANULOPOIESIS
Authors: Maloney Mary A. , Patt Harvey M. , Lund John E.
Published: May 2008

A simple analysis was developed to compare granulocyte production in marrow with granulocyte turnover in peripheral blood of the dog. the analysis is anchored to the relative number of granulopoietic and erythropoietic cells that are flashlabeled with tritiated thymidine. This provides a convenient measure of relative production rates, since there is little, if any, difference in the duration of the respective DNA synthesis periods. the latter was confirmed in the present work by comparison of myeloid and erythroid cells in respect to (1) labeled mitosis curves and (2) changes in labeling intensity with constant infusion of tritiated thymidine. the ratio of flash‐labeled granulocyte to erythrocyte progenitors was unity (1.02 ± 0.05) in the eight dogs studied, which means that gross production rates were essentially the same. Since net production as revealed by peripheral blood turnover is greater for erythrocytes than for granulocytes, it follows that there must be some ineffective granulopoiesis. This may correspond to over half of the total production. It is suggested that this phenomenon, which apparently occurs in man as well as in dog, could represent an important feature of granulocyte regulation.
THE f NUMBER OF PRIMARY TRANSPLANTED SPLENIC COLONY‐FORMING CELLS
Authors: Hendry J. H.
Published: May 2008

The proportion of murine haemopoietic stem cells that settled in the spleen, after transplanting spleen cells into lethally‐irradiated recipient mice, was found by comparing the number of spleen colonies obtained by transplanting a whole spleen with an estimate of the total number of colony‐forming units (CFU) present in the intact spleen. the latter number was estimated assuming that endogenous spleen colonies were produced from surviving spleen‐derived CFU which exhibited the same survival parameters as transplanted CFU.

Account was taken of the post‐irradiation loss of CFU from the spleen in the endogenous assay, which was found to be a reasonably constant factor for doses higher than about 100 rad X‐rays.

The total measured number of CFU/spleen from transplantation was less than the number calculated in the intact spleen by a factor, the primary f number, of 0.03 ± 0.02.
KINETIC AND HISTOLOGICAL CHANGES OF A SERIALLY TRANSPLANTED MOUSE TUMOUR
Authors: Begg A. C.
Published: May 2008

A serially transplanted mouse tumour, NT1, was studied histologically and by autoradiography using tritiated thymidine at three stages in its transplant history: after two, seventeen and twenty‐seven passages. the growth rate of the tumour decreased progressively with increasing passage number, and the mean cycle time of the tumour cells increased from 21 hr to 34 hr between the seventeenth and twenty‐seventh passages. Histologically the tumour changed from having an epithelial structure (second passage), to having a mixed structure with at least two histologically different regions (seventeenth passage), to having a fibrous structure (twenty‐seventh passage). Radiation response experiments were carried out on the second and twenty‐seventh passaged tumours, the results of which are consistent with the kinetic and histological changes.
EFFECTS OF HYDROXYUREA ON THE KINETICS OF COLONY FORMING UNITS OF BONE MARROW IN THE MOUSE
Authors: Vassort F. , Frindel E. , Tubiana M.
Published: May 2008

The number of nucleated bone marrow cells, the number of CFU and the number of DNA‐synthesizing cells in the mouse were studied after injection of hydroxyurea. It was found that one injection provokes a partial synchronization of surviving cells and probably stimulates the transition of CFU from the quiescent to the cycling state. the changes of the proportion of CFU in the S phase makes it possible to estimate approximately a cell cycle duration of about 12 hr.
CHANGES IN THE DNA SYNTHETIC PERIOD DURING THE PHASE OF RAPID GROWTH IN CULTURED DIPLOID FIBROBLASTIC CELLS
Authors: Moore Ruth C.
Published: May 2008

The DNA synthetic period in diploid fibroblastic cell populations was studied during the phase of rapid growth in vitro, using the labelled mitotic wave method and quantitative autoradiography.

It was found that the length of the DNA synthetic period increased progressively, from early passage levels, with the number of generations in vitro. the increase was mainly in the time taken to synthesize the first 50%, and especially the first 10%, of DNA.

The change was detectable despite the complication due to a low level of tritium incorporation after the removal of tritiated thymidine from the cultures.
The Automatic Analysis of Flm Curves
Authors: Takahashi Manabu , Hogg Joseph D. , Mendelsohn Mortimer L.
Published: May 2008

Abstract. Seven parameters of the cell cycle are extracted from experimental FLM data by computer using a completely automated, least‐squares, regression analysis. the procedure is based on a model of the cell cycle with four phases, three coefficients of variation, and a Poisson process of cell progression. TM is estimated separately, using mitoses per labeled cells over the first cycle. Beginning with raw data, the computer calculates initial estimates of the parameters, uses these estimates to generate a synthetic FLM curve, and then measures a weighted mean square deviation of fit between the data and the curve. By a process of iteration, involving a three‐dimensional Newton‐Raphson method for mean transit times and an orthogonal search for coefficients of variation, the measure of fit is progressively minimized. Eighteen experimental data sets have been analysed successfully. Several procedures for the evaluation of the analysis are described.
STUDIES ON LIVER REGENERATION: II. EFFECTS of PHENOBARBITAL ON the ONSET and PATTERN of RAT LIVER REGENERATION FOLLOWING PARTIAL HEPATECTOMY
Authors: BÜRKI K. , SCHINDLER R. , PFENNINGER M.
Published: May 2008

Abstract. Partially hepatectomized rats were given a single intraperitoneal injection of a phenobarbital solution or of water immediately after surgery. At various time intervals following the operation, the animals were injected with 131 iododeoxyuridine (113IDU), sacrificed 2 hr later, and radioactivity retained in formalin‐fixed liver tissue was determined as a measure of DNA synthesis at the time of administration of the labeled precursor. In control animals without phenobarbital treatment, 131IDU incorporation into liver began to increase between 14 and 16 hr after partial hepatectomy. Phenobarbital treatment (0.1 mg per g of body weight) resulted in a delay of the increase in 131IDU incorporation by several hours. This delay was observed in animals subjected to partial hepatectomy in the morning as well as in those operated on in the evening. After phenobarbital treatment, the increase of mitotic activity was either delayed or occurred more slowly. the results are compared with the reported effects of partial hepatectomy on the time course of microsomal enzyme induction by phenobarbital.
INFLUENCE OF METABOLIC DNA ON DETERMINATIONS OF THE CELL CYCLE
Authors: Pelc S. R.
Published: May 2008

Abstract. Evidence in favour of labelling of DNA in excess of requirements for mitosis was found in adult organs showing no mitosis (heart muscle and brain), in organs with low mitotic indexes (liver, seminal vesicle) and, more recently, in the small intestine of rodents, in bone formation and in growing roots of Vicia faba. A survey of published data showed higher labelling indexes than would be expected from the data for S, M and tc deducted from labelled mitoses curves. to improve the accuracy of the data needed for a complete assessment the duration of mitosis (M) and the proportion of cells which are no longer in the mitotic cycle in the crypts were determined using Colcemid. the fact that all cells in the villi are derived from the crypts and that there is no cell‐loss in the villi was checked by cell‐counts.

The results show that 3040%of the labelled nuclei found in crypts of the jejunum of mice at 1 hr after injection of 3H‐thymidine do not proceed to mitosis.

The labelling after the last mitosis is interpreted as formation of the metabolic DNA necessary for the function of the differentiated cells in the villi. There is some evidence that metabolic DNA necessary for the processes of mitosis might be lost
KINETICS OF THE INNER ENAMEL EPITHELIUM IN THE ADULT RAT INCISOR DURING ACCELERATED ERUPTION
Authors: Zajicek Gershom , Michaeli Yael , Weinreb Max M.
Published: May 2008

Inner enamel epithelial (IEE) cell production was compared in accelerated and normal eruption (control). Each group consisting of thirty rats received 1 μCi/g tritiated thymidine. The animals were sacrificed at short time intervals up to 14 hr after injection. The excised incisors were cut mid‐sagittally and processed autoradiographically.

The fast growing incisor produces twice as many cells as the control. Increased cell production is achieved in two ways: proliferative pool expansion (by 25.5%) and generation time (tc) shortening to 16 hr (tc= 23 hr in the control). Generation time shortening resulted mainly from a diminution in tg1= 8.6 hr (tg1= 14.1 hr in the control) and ts which equaled 5.5 hr (ts= 7 hr in control). Mitotic times which equaled 0.4 hr and tg2, 1.5 hr were identical in both groups.

The eruption/IEE cell production ratio equals 1.1 in both groups.
THE SYNTHESIS OF PHOSPHOLIPIDS IN THE NUCLEUS AND NUCLEAR MEMBRANE OF SYNCHRONIZED HeLa CELLS
Authors: Pegoraro Luigi , Galanti Norbel , Stein Gary , Baserga Renato
Published: May 2008

HeLa cells were synchronized by a double thymidine block and pulse labeled at different stages of the cell cycle with 3H‐choline. The specific activity of phospholipids extracted from the cell, the nucleus and the nuclear membrane showed a progressive increase from S to G1; the incorporation of choline into phospholipids of asynchronous cells showed a specific activity intermediate between the values of S and G1 cells. Similar results were obtained when 32phosphorus was used as a precursor instead of choline. Thin layer chromatographic analysis of phospholipids extracted from cells in S and from cells in G1 failed to show any difference in the distribution of radioactivity among the various phospholipid classes.

Choline uptake by HeLa cells in different phases of the cell cycle did not show significant variations. However, during the synchronization process, shortly after the addition of excess thymidine, an increased uptake of choline by cells and an increased incorporation of choline into phospholipids were found. The results indicate that some of the changes occurring in phospholipids synthesis may not be cell cycle dependent, but may be the effect of the synchronizing process.
RADIATION EFFECTS ON CELL POPULATIONS IN THE INTESTINAL EPITHELIUM OF MICE AND ITS THEORY
Authors: Sato F. , Muramatsu S. , Tsuchihashi S. , Shiragai A. , Hiraoka T. , Inada T. , Kawashima K. , Matsuzawa H. , Nakamura W. , Trucco E. , Sacher G. A.
Published: May 2008

Mice were exposed to 1000 R of X‐rays to their trunks and sacrificed every day up to the tenth day after exposure. Cell counts were made on histological sections of the duodenum. The cell counts in the crypts were reduced to about 50% of the control value on the first day after exposure. The cell counts began to recover on the third day and an overshoot of 170% was observed on the fourth day; thereafter the crypt cell counts tended to return to the control level. The cell counts on the villi reached their minimum value on the third day after exposure. Following an overshoot on the sixth day, the villus cell counts returned to the control level by the tenth day. The above experimental results were analysed using a two‐compartment model with a feedback term. A logistic proliferation was assumed for the proliferative crypt cells, while for the postmitotic villus cells the compartment was assumed to be a first in‐first out type. The calculated results with this model are in general consistent with the experimental ones. The model seems to possess some essential features of the dynamics of cell renewal in the intestinal mucosa.
REGULATION AND KINETICS OF SPERMATOGONIAL PROLIFERATION IN ARENICOLA MARINA (ANNELIDA, POLYCHAETA) I. THE ANNUAL CYCLE OF MITOTIC INDEX IN THE TESTIS
Authors: Olive P. J. W.
Published: May 2008

The annual variation in the mitotic index of the testis of Arenicola marina after 48 hr treatment with colchicine has been determined. This mitotic index in the population is distributed log‐normally. The mean mitotic index is low in winter but increases during the spring to a maximum in early summer. The mean mitotic index remains high until September when it decreases temporarily. There is a second minor increase in the mean mitotic index prior to spawning.

Decerebration of animals prior to the spring increase in the mitotic index did not prevent this increase occurring in decerebrate animals maintained in the laboratory. Removal of the coelomic gametes was effective in stimulating the testicular mitotic index only when performed during the period of low mitotic activity in early autumn.
REGULATION AND KINETICS OF SPERMATOGONIAL PROLIFERATION IN ARENICOLA MARINA (ANNELIDA, POLYCHAETA) II. KINETICS
Authors: Olive P. J. W.
Published: May 2008

The rate of accumulation of mitoses in the testis of Arenicola marina has been estimated by the colchicine method. The rate is low in February but increases during spring to a maximum in June. The rate remains high during July and August but decreases in September. A second temporary and minor rise was observed in October or November prior to spawning.

The rate of accumulation of mitoses (with respect to the duration of metaphase arrest) is logarithmic from February to June, but is arithmetic during the latter part of the reproductive cycle (July‐October). The transition from one phase to the next coincides with the initiation of spermatocyte release from the testis into the coelom.

The rate of accumulation of mitoses has also been recorded in testes cultured in vitro. The rate in vitro does not differ from that in vivo in May when the rate is high, but in September when the rate in vivo is depressed, culture in vitro significantly increases the mitotic rate.

The cell cycle time of the proliferating spermatogonia has been estimated by a modified per cent labelled mitosis technique. The cell cycle time is unusually long (in excess of 20 days) and the G2 period is at least 5 days. It is suggested that the testis of A. marina is an exponentially growing cell population from February until early June when coelomic spermatocytes first appear. The rate of cell release then temporarily exceeds the rate of renewal: eventually they become equal and the testis remains in steady state until September when the mitotic rate is depressed due to the presence of maturing spermatocytes. The depression of the mitotic rate in September is achieved by the arrest of spermatogonia in G2. Explanting the gonads in organ culture removes the inhibition and causes an increased flow of cells from G2 into mitosis.
OBSERVATIONS ON HUMAN MONOCYTE KINETICS AFTER PULSE LABELING
Authors: Whitelaw D. M.
Published: May 2008

Monocyte kinetics were studied in seven hematologically normal individuals using in vivo pulse labeling with tritiated thymidine. Although occasional labeled cells appear in the peripheral blood within 4 or 5 hr of the administration of label, a significant outflow from the marrow begins 13–26 hr later. This interval is occupied by the G2 and M phases of the mitotic cycle since mitotic cells are not observed in the peripheral blood. The duration of the DNA synthesis phase of monocytes is measured at 34 hr ≈ 1.8 hr. Cells do not enter this phase while circulating since exposure of circulating cells to tritiated thymidine does not result in any uptake. If monocytes are not ‘end’cells which have completed their mitotic activity before leaving the marrow they must at least be inhibited from further proliferative activity until they are permanently sequestered in other tissues.

The generation time is probably not less than 40 hr and data derived from the mean grain counts of labeled cells suggest that it is often more than 70 hr. The total daily output of monocytes in man is 9.4 × 108 cells per 24 hr ≈ 3.3 × 108.

Cells leave the bloodstream with a half‐time of about 71 hr thereby proving themselves to be considerably more durable than neutrophils which have a half‐life in the neighborhood of 6 hr.
SUBCULTIVATIONS, SPLITS, DOUBLINGS, AND GENERATIONS IN CULTURES OF HUMAN DIPLOID FIBROBLASTS
Authors: Good Phillip I.
Published: May 2008

Mathematical expressions are provided relating subcultivations to population doublings and population doublings to generations. Account is made for the increasing number of cells which do not attach upon subcultivation as well as the increasing number of non‐dividers. The expressions reconcile published differences in longevity and reveal that the in vitro lifetime of human diploid cells measured in cell generations is far greater than previously suspected.
RELATION BETWEEN THE CIRCADIAN RHYTHMS OF MITOTIC RATE AND CHOLESTEROL‐7α‐HYDROXYLASE ACTIVITY IN THE REGENERATING LIVER
Authors: Van Cantfort Jacques J. , Barbason Hervé R.
Published: May 2008

The evolution of mitoses and cholesterol‐7α‐hydroxylase activity were studied in parallel in the regenerating liver after a partial hepatectomy performed at two different hours of the nycthemeral period, i.e. 10 a.m. and 8 p.m.

The mitotic index was used to assess the function of cell division while cholesterol‐7α‐hydroxylase activity was taken as a test of the tissue‐specific function. The results showed a different evolution of these two functions according to the time of the surgery. The data indicated that a mutually exclusive relationship took place between the function of cell‐division and the tissue‐specific function.

These observations suggested that, during liver regeneration, the derepression of the genes coding the enzymes of these two different functions takes place in a complementary fashion, at two different phases of the nycthemeral period.
MULTIPLICATION OF HAEMOPOIETIC COLONY FORMING UNITS (CFU) IN MICE AFTER X‐IRRADIATION AND BONE MARROW TRANSPLANTATION
Authors: Vos O.
Published: May 2008

Kinetics of the multiplication of haemopoietic CFUs was studied in lethally irradiated mice receiving various numbers of syngeneic bone marrow cells. After transplantation of a small number of bone marrow cells, the growth rate of CFU in femoral bone marrow appeared to decrease after about 10 days after transplantation, before the normal level of CFU in the femur was attained. In the spleen it was found that the overshoot which was observed about 10 days after transplantation of a large number of bone marrow cells is smaller or absent when a small number of cells is transplanted. Experiments dealing with transplantation of 50 x 106 bone marrow cells 0, 4 or 10 days after a lethal irradiation indicated that the decline in growth rate of CFUs about 10 days after irradiation could not be attributed to environmental changes in the host.

The results are explained by the hypothesis that a previous excessive proliferation of CFUs diminishes the growth rate thereafter. This hypothesis is supported by experiments in which 50 x 106 bone marrow cells derived from normal mice or from syngeneic chimaeras were transplanted. The slowest growth rate was observed when bone marrow that had been subjected to the most excessive proliferation in the weeks preceding the experiment was transplanted.
CELL KINETICS OF GROWTH CARTILAGE IN THE RAT TIBIA II. MEASUREMENTS DURING AGEING
Authors: Walker K. V. R. , Kember N. F.
Published: May 2008

A number of cell kinetic techniques using labelled thymidine and autoradiography have been applied to study growth cartilage in the rat tibia during ageing. No change in the duration of the synthesis phase was found from 4 to 13 weeks of age but there was a reduction in cell proliferation rate during this period. Measurements of labelling index, proliferation zone size and height of hypertrophic cells were used to calculate the growth rate of the bone from 7 days to 1 year. The results agreed well with radiographic measurements of bone growth.
QUALITATIVE EFFECT OF CYTOSINE ARABINOSIDE UPON TRANSCRIPTION IN CULTURED HUMAN LYMPHOCYTES
Authors: Flickinger R. A. , Roche F. M. , Rodriguez L. V.
Published: May 2008

Previous work has shown that more kinds of DNA‐like RNA are transcribed by more rapidly dividing frog embryo cells than by more slowly dividing cells in another region of the embryo (Flickinger & Daniel, 1972). In order to learn if such a difference in transcription is due to the difference in rate of cell division, rather than to differences in RNA and protein synthesis, the compound cytosine arabinoside was used to reduce the rate of cell division in cultured human lymphocytes without decreasing RNA and protein synthesis (Chu & Fischer, 1962; Kim & Eidinoff, 1965; Selagi, 1965). Human lymphocytes were cultured in the presence of cytosine arabinoside (1‐β‐D‐arabinofuranosyl‐cytosine) and the qualitative effect upon transcription ascertained by comparison with normal lymphocytes utilizing the method of DNA‐RNA hybridization. The normal human lymphocytes have been cultured (Moore et al., 1969) in stationary and spinner flasks for about a year at Roswell Park Memorial Institute. In the present work cells from one stationary culture were seeded into spinner flasks containing 150 ml of R.P.M.I. medium No. 1703 plus 10% (v/v) heat inactivated fetal calf serum without antibiotics. Culture medium is added periodically (200 ml each 48 hr) as cell concentrations rise.
REGULATION OF HAEMOPOIETIC STEM CELL TURNOVER IN PARTIALLY IRRADIATED MICE
Authors: Gidali Julia , Lajtha L. G.
Published: May 2008

The existence of a possible local control of CFU turnover was studied in mice in which one tibia only was irradiated (LR mice) and in mice in which one tibia was shielded during whole‐body irradiation (‘TBR’mice). In both the LR and ‘TBR’mice, the increased CFU turnover continued in the irradiated tibiae even after the time when in the unirradiated (shielded) tibiae it returned to normal levels. The early temporary decrease in the CFU numbers in the shielded tibiae of ‘TBR’mice is attributed to a temporary demand for increased differentiation rather than to migration of CFU. The direct control of CFU turnover appears to be local in nature, in contrast to the stimulus for CFU differentiation.
THE TEMPO OF LYMPHOCYTE RECIRCULATION FROM BLOOD TO LYMPH IN THE RAT
Authors: Ford W. L. , Simmonds S. J.
Published: May 2008

Radioactively labelled thoracic duct lymphocytes were obtained either by incubation in vitro with 3H‐uridine or 14C‐uridine or by giving potential donors repeated injections of 3H‐thymidine finishing 17 days before thoracic duct cannulation. These labelled TDL were injected i.v. into syngeneic recipients which had been subjected to splenectomy and thoracic duct cannulation on the previous day. The tempo of lymphocyte recirculation from blood to lymph was reflected by the time at which radioactivity was recovered in the thoracic duct lymphocyte output of the recipient. This was measured by scintillation counting of 2‐hourly fractional collections for 36 hr after the injection. Two lines of evidence showed that the majority of small lymphocytes which label intensely with radioactive uridine in vitro were uniform in their ‘migration potential’with a modal blood to lymph transit time of 14–18 hr. By contrast the cells which were labelled in vivo with 3H‐thymidine included a slower population with a modal transit time of 24–28 hr. These conclusions can be more fully interpreted in the light of recent evidence on thymic‐independent (‘B’) lymphocytes.
CELL POPULATION KINETICS OF PLUCKED AND UNPLUCKED MOUSE SKIN I. UNIRRADIATED SKIN
Authors: Hegazy M. A. H. , Fowler J. F.
Published: May 2008

A detailed study of the cellular proliferation kinetics in interfollicular plucked and unplucked mouse skin has been made in Swiss albino mice, using tritiated thymidine autoradiography. Diurnal variations in mitotic and labelling indices were demonstrated in both systems.

The mean cell cycle times for unplucked and plucked skin were estimated by four different methods and found to be 100 ± 10 and 47 ± 3 hr respectively. Most of the difference was due to the shortening of G1 phase after plucking. Repeated labelling at intervals shorter than the DNA synthesis times resulted in all the basal layer cells becoming labelled, so that the growth fraction was unity, in unplucked and plucked skin.

A well‐defined second wave of labelled mitoses was seen at about 100 hr after labelling the unplucked (i.e. normal) mouse skin.

A double labelling technique using 14C‐TdR and 3H‐TdR with a single layer of emulsion gave reasonable values for the duration of the DNA synthesis phase.
THE EFFECT OF METHYL CCNU (NSC‐95441) ON THE CELLULAR KINETICS OF NORMAL AND LEUKEMIC MURINE TISSUES IN VIVO
Authors: Young Robert C.
Published: May 2008

The effect of MeCCNU on the cellular kinetics of normal and leukemic murine tissues is examined in vivo. A prolongation in the S phase is noted after doses of MeCCNU as low as 4 mg/kg, and this prolongation persists for approximately 4 hr after the dose. No persistent alteration in the growth fraction is produced by MeCCNU. The generation time of the cells regrowing after MeCCNU is slightly prolonged, compared to normal L1210 leukemia. Simultaneous studies on ascites tumor, normal bone marrow, and normal gastrointestinal mucosa, using the in vivo uptake of 3H‐thymidine into DNA, have shown a differential effect on the tumor and normal tissues.
KINETICS OF MURINE HAEMOPOIETIC CELL PROLIFERATION IN DIFFUSION CHAMBERS
Authors: Bøyum Arne , Breivik Harald
Published: May 2008

Murine bone marrow cells were cultured in cell impermeable diffusion chambers in the abdominal cavities of mice. The kinetics of granulocyte and macrophage formation were studied by stathmokinetic and autoradiographic techniques. During the period of most rapid growth of proliferative granulocytes, their generation time and its different phases were: tc∽ 8 hr, tG1∽ 1·5 hr, ts∽ 5·5 hr, tG2∽ 0·7 hr and tM∽ 0·25 hr.

The generation time of macrophages and their precursors was approximately 8 hr. Formation of macrophages was significantly reduced when chamber inoculum was increased, as judged by 3H‐TdR labelling index.
A MATHEMATICAL MODEL OF THE CELL CYCLE OF L5178Y
Authors: Roti Roti J. L. , Okada S.
Published: May 2008

Given the starting cell cycle age distribution and the growing conditions, the model developed through modification of Hahn's vector analysis predicts the age distribution of the population after a growth period. The model was able to simulate changes in growth and the per cent of cells in each stage of the cell cycle for cells growing in excess thymidine, in colcemid, in normal medium, and after successive treatments of these drugs, specifically the chemical synchronization method of L5178Y cells.
CYTOKINETICS OF THE S‐180 ASCITES TUMOR SYSTEM
Authors: Schiffer L. M. , Nelson Janet S. R. , Dilettuso Barbara , Migliorato Dolores , Randolph William
Published: May 2008

The cytokinetics of the S‐180 mouse ascites tumor system was determined on Days 2, 4, 6 and 9 of growth. Studies included volume tumor growth, per cent labeled mitoses curves, and repeated injections of tritiated thymidine. It was possible to extrapolate the cytokinetic compartment values to Day 0 of growth. Results indicate that the growth fraction of the S‐180 system remains close to 1 throughout its growth, with progressive lengthening of G1, S and G2 times. Cell loss is minimal through 6 days but becomes significant thereafter. A theoretical growth curve constructed from cytokinetic values is similar to the actual volume growth curve.
HYDROXYUREA EFFECTS IN THE C3H MOUSE II. MAMMARY TUMOR CELL KINETICS
Authors: Dethlefsen Lyle A. , Riley Reba M.
Published: May 2008

The cellular kinetics of C3H mouse mammary tumors were studied following a single dose (3 mg/g body weight) of hydroxyurea (HU). This dose was large enough to cause a significant perturbation in the growth curves of these tumours. This was accomplished by labeling the cells with tritiated 5‐iodo‐2′‐deoxyuridine and performing detailed autoradiographic analysis. This dose of HU caused a temporary inhibition in growth and completely inhibited DNA synthesis for 4–5 hr. The HU‐killed cells (pyknotic and karyorrhectic) reach a maximum around 10–12 hr and are apparently all removed in about 1 day. Tumors from a fast‐growing line (S102F) showed some evidence for cell synchrony upon recovery from HU inhibition but desynchronization occurred within one cell cycle. The cell generation time was not decreased during the acute recovery phase, but the growth fraction shifted from 0·6 to 1·0, and the data suggested that the normal flow of cells from the proliferating pool to the degenerate pool was temporarily interrupted. The cellular kinetic parameters have probably returned to normal by 48 hr after the HU injection.
LOCAL AND SYSTEMIC CONTROL OF GRANULOCYTIC AND MACROPHAGE PROGENITOR CELL REGENERATION AFTER IRRADIATION
Authors: Chan S. H. , Metcalf D.
Published: May 2008

Agar cultures of C57BL bone marrow cells were used to determine colony stimulating factor (CSF) and serum CSF‐inhibitor levels in C57BL and BALB/c mice following irradiation. Whole‐body irradiation caused an acute, dose‐dependent, rise in serum CSF levels and fall in CSF‐inhibitor levels. The regeneration of granulocytic and macrophage progenitor cells (in vitro CFCs) in the femur after 250 rads whole‐body irradiation was preceded or paralleled by a fall in serum CSF‐inhibitors and a dramatic rise in the capacity of bone‐adherent cells in the marrow (‘stromal cells’) to produce material with colony‐stimulating activity. No comparable changes were observed in the activity of marrow haemopoietic cells during regeneration or in the lungs or spleen. A similar rise in the activity of bone‐adherent cells was observed in shielded femurs during regeneration of in vitro CFCs.

Regeneration of granulocytic and macrophage progenitor cells following irradiation may be regulated by fluctuations in circulating CSF‐inhibitor levels and local production of CSF within the marrow cavity.