Duration Of DNA Synthesis Research Articles

Regulation of DNA Replication in Early Embryonic Cleavages.

Early embryonic cleavages are characterized by short and highly synchronous cell cycles made of alternating S- and M-phases with virtually absent gap phases. In this contracted cell cycle, the duration of DNA synthesis can be extraordinarily short. Depending on the organism, the whole genome of an embryo is replicated at a speed that is between 20 to 60 times faster than that of a somatic cell. Because transcription in the early embryo is repressed, DNA synthesis relies on a large stockpile of maternally supplied proteins stored in the egg representing most, if not all, cellular genes. In addition, in early embryonic cell cycles, both replication and DNA damage checkpoints are inefficient. In this article, we will review current knowledge on how DNA synthesis is regulated in early embryos and discuss possible consequences of replicating chromosomes with little or no quality control.

Flow cytometry after bromodeoxyuridine labeling to measure S and G2+M phase durations plus doubling times in vitro and in vivo

This protocol describes methods for calculating the proliferative parameters of cell populations. The basis of the technique is to label cells, either in vitro or in vivo, with halogenated thymidine analogs, such as bromodeoxyuridine (BrdU). Bivariate DNA-BrdU flow cytometry is used to analyze the BrdU-labeled and unlabeled cells. The enumeration of specific cohorts of cells that either have or have not divided in the interval between labeling and cell/tissue sampling permits the calculation of the potential doubling time (T(pot)) of the population, plus the durations of DNA synthesis (T(S)) and the G2+M phase (T(G2+M)) of the cell cycle. The method provides information that is not otherwise available, namely inhibition of DNA synthesis and the separate evaluation of cell-cycle effects in BrdU-labeled and unlabeled subpopulations. Ethanol-fixed samples take 1 d to prepare and stain, and reliable parameter estimates might be obtained from measurements made at a single time point after labeling.

Relationship between potential doubling time ( Tpot), labeling index and duration of DNA synthesis in 60 esophageal and 35 breast tumors: is it worthwhile to measure Tpot?

Background: In recent years T pot (potential doubling time) has been measured before treatment in human tumors in an attempt to estimate the proliferation taking place during a course of irradiation. T pot is defined as T s/ LI, where T s is the duration of DNA synthesis and LI is the labeling index (proportion of cells synthesizing DNA). T s is more difficult to measure than LI, so the question arises whether variation introduced during the determination of T s is compensated by the theoretically better relevance of the quotient T pot than of LI alone. It is not clear from comparisons with clinical outcome whether T pot is a useful indicator of proliferation or whether LI is more prognostic, as suggested by a currently ongoing multicenter analysis elsewhere. Therefore, we investigated intercomparisons between T pot and its components LI and T s in two in their proliferation rates contrasting types of tumor where multiple biopsies were taken from each tumor. Materials and methods: Sixty patients with esophageal carcinoma and 57 patients with breast cancer were included in this study. All patients were injected with IUdR 6–8 h before surgery. From each tumor three to five biopsies were taken at surgery. Using flow cytometry, LI and T s were measured on all biopsies in order to calculate T pot. Logarithmic transformations of the distributions were used to examine correlations. Kappa-tests were used to assess how reliable an LI value could be in predicting the corresponding T pot. Results: T s and LI were not completely independent, based on the within-tumor coefficients of variation ( CV w). The ratio of between-tumor coefficient of variation ( CV b) to the CV w suggested that the discriminative power of T pot was higher than LI for esophagus, but the reverse in breast tumors, which had a larger range. Pearson correlation coefficients were high for log T pot versus log LI in both types of tumor, but the predictive power was low, as shown by κ-values of only 0.3–0.41 starting with LI and trying to predict the corresponding value of T pot. Increasing widths of a central `gray zone' were investigated for improved discrimination between fast and slow proliferation. Multiples of the within-tumor standard deviation, equally on each side of the median, were used to vary the width of the gray zone. Without a gray zone no more than 70% successful matching was obtained in esophagus tumors, compared with 80% in breast tumors. However, by excluding about half of the esophageal tumors an 80% success rate was achieved. In breast tumors over 90% matching was obtained more easily, keeping 80% of the tumors classifiable. For both tumor types correlations between T s and T pot were weak, with a trend towards short T s associated with short T pot and also with low LI. The latter correlation was significant for esophageal tumors and resulted in T pot values having a smaller range than the LIs. Conclusion: Although there were good correlation coefficients between T pot and LI, the predictive power of either from the other was not reliable, except by excluding a significant number of tumors close to the medians. The predictive value of LI for T pot was higher for breast tumors because the spread in cell kinetic measurements was wide. Until more clinical data become available on outcome in comparison with LI or T pot, it is still worthwhile to measure T pot and to assess the prognostic value of both LI and T pot in relation to outcome.

Cell kinetic measurements in prostate cancer

Two approaches have been suggested for escalating the total dose in radiotherapy treatment of prostate cancer. One is conformal radiotherapy; the other is hyperfractionation using many small fractions. Both imply some possible prolongation in overall treatment time. To judge whether prolonged treatment schedules would be detrimental, it is necessary to know the proliferation rates in human prostate tumors, specifically, the potential doubling time (Tpot). There is a lack of data on this parameter in the literature. Seven patients with adenocarcinoma of the prostate were studied. A tracer dose of 100 mg/m2 of IUdR was infused intravenously 4-12 h before biopies were taken. Biopsies were fixed in 70% ethanol, stored at 4 degrees C, and later prepared and stained by standard methods for flow cytometry, using the red fluorescence signal for DNA and the green fluorescence signal (fluorescein isothiocyanate) for 5-iodo-2'-deoxyuridine. The duration of DNA synthesis (Ts) was determined by the relative movement (RM) method, knowing the interval between tracer administration and biopsy. Tpot was calculated as the quotient of Ts by labeling index (LI). In two of the seven tumors the LI was too low (<0.6%) for a reliable estimate of RM to be made, so no determination of Tpot was possible for these tumors. The mean LI values in the other five tumors were 2.4%, 1.4%, 1.0%, 3.0%, and 0.9%. The durations of Ts were 13.2, 9.5, 10.0, 11.7, and 12.7 h, respectively. The resulting values of Tpot were 23, 28, 42, 16, and 61 days, respectively. The low labeling indices in prostate tumors, also reported by others, made estimation of Ts by RM impossible in about a third of these tumors. However, five tumors yielded long estimates for Tpot, implying that prolongation from 6 to about 8 weeks should not be detrimental.

Influence of recipient oocyte cell cycle stage on DNA synthesis, nuclear envelope breakdown, chromosome constitution, and development in nuclear transplant bovine embryos

Nuclear transplantations into metaphase II (MII) and S phase oocyte cytoplasm were performed to investigate the influence of recipient cell cycle stage on nuclear function and development of bovine nuclear transplant (NT) embryos. Rate of inactivation of histone H1 kinase and duration of DNA synthesis in activated oocytes were determined. The proportion of S phase blastomeres in in vivo produced day 5.5 bovine embryos was measured. DNA synthesis was also assessed in NT embryos after transfer into MII and S phase cytoplasm. MII NT embryos were produced by fusing a blastomere into a MII oocyte; the fusion pulse served to activate the oocyte. S NT embryos were produced by fusing a blastomere into an early S phase oocyte electrically activated 4 h prior to fusion. Nuclear envelope structure, chromosome constitution, and extent of development were examined in MII and S NT embryos. Histone H1 kinase activity dropped to baseline within 2 h of electrical activation. A second electrical pulse did not alter H1 kinase activity when delivered 4 h after the first pulse. The frequency of S phase blastomeres in day 5.5 bovine embryos ranged from 79% to 100%, depending on the duration of culture in 3H-thymidine. Nuclear transplantation into MII cytoplasm resulted in a transient drop in DNA synthesis over 3.5 h. DNA synthesis resumed at 4.5 h post activation (hpa), concomittantly with initiation of DNA replication in activated oocytes. In contrast, DNA synthesis was not interrupted after transfer into S phase cytoplasm. DNA synthesis persisted until 13.5 hpa, as in activated oocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Double labelling of cells with tritiated thymidine and bromodeoxyuridine reveals a circadian rhythm‐dependent variation in duration of DNA synthesis and S phase flux rates in rodent oral epithelium

We describe a double labelling method for estimating the duration of DNA synthesis (Ts) and the flux of cells into and from the S phase of the cell cycle, based on labelling with tritiated thymidine [( 3H]TdR) followed by bromodeoxyuridine (BrdU) and combining immunohistological detection of BrdU with conventional autoradiography. In practice, the change in size of a window of double labelled cells occurs as the time interval between the two labels increases. In mouse tongue epithelium there is a marked circadian variation in the number of cells in DNA synthesis. From 0900 to 1500 h this labelling index (LI) falls, but from 2100 to 0300 h it increases. Our results show that the circadian decrease in LI is associated with a short Ts (5.8 +/- 0.3 h), a high S phase efflux and an initially low influx of cells from G1 into S. Conversely, the rising circadian LI is associated with a longer Ts (9.4 +/- 0.1 h), an initially low efflux and a moderate to high influx. Two time-points exist on the circadian LI curve when influx and efflux rates change abruptly. At 0100 h the efflux rate rises from low (5 cells %/h) to high (15-16 cells %/h) and simultaneously the influx rate changes from high to low. Similarly at 1300-1400 h, efflux rate falls from high (19-20 cells %/h) to low (4-8 cells %/h) values and influx rates change from low to high. This double labelling method has revealed that the duration of DNA synthesis varies across the circadian cycle, as do influx and efflux values which generally fall within a discrete range of high or low values. The timing of the changes in flux suggests the presence of two 'control' points on the circadian LI cycle that were previously unrecognized.

Age‐related changes in the cell kinetics of rat foot epidermis

The durations of the cell cycle and its component phases have been determined for the basal layer of the epidermis of the skin from the upper surface of the hind foot of the rat using single pulse [3H]-thymidine labelling and the percent labelled mitosis (PLM) technique. Rats of three age groups were used, namely 7, 14 and 52 weeks. The duration of DNA synthesis (Ts) and the G2 plus M phase (TG2 + M) were comparable in 7-week and 52-week-old rats (P greater than 0.1). The major difference between 7-week and 52-week-old rats was in the duration of the G1 phase (TG1). In 7-week-old rats TG1 was 15.0 +/- 0.8 h and in 52-week-old rats TG1 was 31.2 +/- 3.5 h. A consequence of this variation was that the overall duration of the cell cycle was longer in 52-week-old rats (53.9 +/- 5.3 h) than in 7-week-old rats (30.1 +/- 1.3 h). Difficulties were found in fitting a simple curve to the PLM data for 14-week-old rats. This suggests that the proliferative cell population of the epidermis of rats of this age group may be heterogeneous. A satisfactory fit to the data was obtained using a computer model which assumed that the proliferative population of the epidermis of 14-week-old rats was a mixture of cells with cell cycle parameters the same as those of the 7-week and the 52-week-old rats. These two sub-populations of relatively slowly and rapidly proliferating cells were present in the ratio of 2:1.

The cell kinetics of the epidermis and follicular epithelium of the rat: variations with age and body site.

The skin from rats of differing age was used to quantify variations in the cell kinetics of the epidermis and the follicular epithelium of different body sites. Four parameters were assessed, namely the basal cell density (BCD), the labelling index (LI), the duration of DNA synthesis (ts) and the basal cell turnover time (tT). The BCDs of the epidermis of the dorsum and the upper surface of the foot were similar in rats of 7, 14 and 52 weeks of age, but there was an indication of a progressive decline with increasing age in the BCD of the epidermis of the ear and tail. There were no age-related changes in the length of ts in any of the four body regions. The rate of cell proliferation, as indicated by the values of the LI and tT, was relatively rapid in the epidermis of the dorsum, foot and tail of rats aged 7 weeks (LI greater than 12%; tT less than 80 h). In rats aged 14 weeks this rate of proliferation was maintained in the epidermis of the dorsum. However, in the foot and tail the rate of cell proliferation was decreased (LI less than 10%; tT greater than 85 h). A fall in the rate of proliferation of the epidermis of the dorsum was only seen in 52-week-old animals. In these animals the rates of proliferation in the foot and tail were similar to those at the age of 14 weeks. In the epidermis of the ear there was no appreciable change in the rate of cell proliferation with age. The values of the cell kinetic parameters varied in the different body sites. For example, in 52-week-old animals values for tT were relatively short in the epidermis of the tail and foot and appreciably longer in the epidermis of the dorsum and ear. Considered overall, values for the cell kinetic parameters of the epidermis were comparable with those for the follicular epithelium. The only major differences between the epidermis and the follicular epithelium were in the upper surface of the foot at 7 weeks of age, and in the tail at 7 and 14 weeks of age, where the LI was higher and the tT shorter in the epidermis than in the follicular epithelium. The relevance of the observed age- and body-site-related variations in the cell kinetics of the epidermis are discussed in relation to previously described differential changes in the radiosensitivity of the skin in this strain of rat.

Cell cycle of normal bladder urothelium in developing and adult mice

The present research has employed a novel, nonradioactive technique to quantitatively study normal urothelial proliferation in foetal, neonatal, juvenile and adult mouse bladder. Using whole mount histological preparations, the total number of urothelial nuclei per mouse bladder, and per given urothelial cell layer, have been assessed to provide data of the (unstimulated) kinetic behaviour of basal urothelial cells (the proliferative population), to analyse characteristics of the normal urothelial cell cycle. The urothelial cell cycle time increases from 30.6 h (foetal) to 40 weeks (adult), the duration of mitosis from 0.23 h (foetal) to 2.71 h (adult) and the duration of DNA synthesis from 2.52 h (neonatal) to 10.83 h (adult). These are average values for the urothelial cell cycle, which do not preclude the possible existence of proliferative units. The ratio of superficial nuclei to basal and intermediate nuclei, possibly indicative of a urothelial proliferative unit, declines to reach a plateau (1:40) in adult mice. These findings indicate that rapid urothelial proliferation during early murine development was likely to be a) biologically useful, since intrauterine foetal metabolic activity may require a functional bladder urothelium at an early stage, b) kinetically similar to acutely regenerating adult urothelial cells after cytotoxic insult. During murine life, the range of durations of mitosis and DNA synthesis is much less than the range of cell cycle times. Normal unstimulated urothelium of adult mice was confirmed to proliferate slowly.

Human tumour cell kinetics using a monoclonal antibody against iododeoxyuridine: Intratumour sampling variations

Cell kinetic parameters in human tumours were determined by in vivo labelling with iododeoxyuridine (IUdR) followed by flow cytometric analysis of tumour biopsies after staining with a monoclonal antibody against IUdR-DNA. The purpose of this study was to determine the variation in these kinetic parameters from area to area within the same tumour. Each patient received a single i.v. injection of IUdR and the biopsy or operation specimen was taken several hours later. Multiple biopsies were taken or the operation specimen was cut into several pieces. Tumour material was stored in ethanol. Each piece was subsequently processed and stained for analysis separately. The duration of DNA synthesis ( T s ), the labelling index (L.I., percent IUdR-labelled cells) and the potential doubling time ( T pot) were determined for each sample. The mean and standard deviation (variation between pieces) for each parameter was calculated for each tumour. The coefficient of variation (C.V.) provided the measure of intratumoural variation. Thirteen tumours were investigated, 6 of which were transitional cell carcinomas of the bladder and 7 of which were squamous cell carcinomas, mostly of the head and neck. T s values ranged from 4.1 to 17.2 h (mean 9.5 h), L.I. values from 1.6 to 18.6% (mean 9.7%) and T pot values from 2.3 to 15.1 days (mean 7.2 days). Mean C.V.s for T s , L.I. and T pot were 10, 24 and 27%, respectively. Most of the variation in T pot (calculated from the other two parameters), came from the L.I., with T s showing much less intratumoural variations. It is concluded that this kinetic method using low IUdR doses can be successfully applied in human tumours and has sufficient accuracy for predictive assay applications in which tumours need to be classified according to their proliferation rates. Further developments are required to distinguish normal and malignant cells flow cytometrically, particularly for diploid tumours.

Cell population kinetics in pig epidermis: further studies.

The cell population kinetics of the epidermis were studied in 4-month-old pigs. Mitotic figures were confined to the basal cell (L1) and the first suprabasal cell layer (L2). The mitotic index (MI) was 0.17 +/- 0.04% for L1 and 0.08 +/- 0.03% for L2. Labelled nuclei were distributed throughout the viable epidermis, the majority (79.1 +/- 1.1%) were in L1 with 19.5 +/- 1.2% in L2. The labelling indices (LI) in layers L1 and L2 were 7.1 +/- 0.4% and 3.4 +/- 0.1%, respectively. After labelling with two injections of tritiated thymidine [3H]TdR separated by 90 min, the LI increased to 8.2 +/- 0.3% in L1 and to 4.0 +/- 0.2% in L2. This increased labelling confirmed that cell proliferation occurs in both layers, L1 and L2, of the epidermis. The cell production rate (K) in L1 and L2 had an upper limit of 10.7 +/- 1.0 and 6.2 +/- 1.8 cells per 1000 cells per hour respectively. The cell flow rate per hour (cell flux), into and out of the DNA synthesis phase (S), and the duration of DNA synthesis were determined from double-labelling studies with [3H]TdR and [14C]TdR. The cell flux into and out of S was identical and was calculated as 0.6 +/- 0.1%/hr (L1) and 0.5 +/- 0.1%/hr (L2). Values for tS varied from 8 to 10 hr. The cell turnover times (tT) were in the range 89-129 hr and 180-261 hr for L1 and L2, respectively. Log normal curves were fitted to the fraction labelled mitoses data for L1 and L2. Values for tS for cells in L1 and L2 were 9.8 hr and 11.9 hr, respectively. tG2 + 1/2tM was 7.2 hr in L1 and 9.1 hr in L2.

Pig Epidermis: A Cell Kinetic Study

The basal cell density (BCD), labelling index (LI), duration of DNA synthesis (TS) and cell cycle time (TC) have been calculated for the epidermis of pigs in the age range 4-27 months. The BCD declined progressively from 143.4 +/- 6.5 cells/mm at 4 months to 128.8 +/- 8.3 cells/mm at 15 months, whereafter the values showed little change. There was a small decrease in LI with increasing age, from 7.9 +/- 1.5% at 4 months to 5.9 +/- 1.0% at 27 months. However, the change to housing animals outdoors as compared with indoors had a greater effect on the LI (approximately 10%). Severe weathering in the skin of animals housed outdoors resulted in a very high LI (approximately 20%). Neither TS or TC varied significantly with age. TS was within the range 8.8-9.2 hr and TC 127-161 hr. In animals housed outdoors TC was reduced relative to animals housed indoors. The BCD and TS were not affected by housing conditions. The kinetic parameters investigated in the pig were similar to those reported for man.

Control of DNA synthesis in polyploid mammalian cells.

To test the hypothesis that the duration of DNA synthesis is an inverse function of nuclear size or DNA content, the S phase was calculated from PLM analysis for pseudodiploid, tetraploid, and octaploid lines of Chinese hamster cells growing as a monolayer or in suspension. S phase times were found not to be significantly different between polyploid lines and the diploid lines from which they were derived, regardless of the conformation of the nucleus. There is no evidence, therefore, that would implicate the nuclear membrane, or nuclear surface area/volume relationships, in the control of DNA synthesis.

Cell Proliferation in Normal Epidermis

A detailed examination of cell proliferation kinetics in normal human epidermis is presented. Using tritiated thymidine with autoradiographic techniques, proliferative and differentiated cell kinetics are defined and interrelated. The proliferative compartment of normal epidermis has a cell cycle duration (Tc) of 311 h derived from 3 components: the germinative labeling index (LI), the duration of DNA synthesis (ts), and the growth fraction (GF). The germinative LI is 2.7% +/- 1.2 and ts is 14 h, the latter obtained from a composite fraction of labeled mitoses curve obtained from 11 normal subjects. The GF obtained from the literature and from human skin xenografts to nude mice is estimated to be 60%. Normal-appearing epidermis from patients with psoriasis appears to have a higher proliferation rate. The mean LI is 4.2% +/- 0.9, approximately 50% greater than in normal epidermis. Absolute cell kinetic values for this tissue, however, cannot yet be calculated for lack of other information on ts and GF. A kinetic model for epidermal cell renewal in normal epidermis is described that interrelates the rate of birth/entry, transit, and/or loss of keratinocytes in the 3 epidermal compartments: proliferative, viable differentiated (stratum malpighii ), and stratum corneum. Expected kinetic homeostasis in the epidermis is confirmed by the very similar "turnover" rates in each of the compartments that are, respectively, 1246, 1417, and 1490 cells/day/mm2 surface area. The mean epidermal turnover time of the entire tissue is 39 days. The Tc of 311 h in normal cells in 8-fold longer than the psoriatic Tc of 36 h and is necessary for understanding the hyperproliferative pathophysiologic process in psoriasis.

The effect of demonstration of the Brazelton neonatal, assessment scale on the father infant relationship

Acute granulocytic hyperplasia was produced in mice by injection of endotoxin and, using the labelled mitosis method, the duration of DNA synthesis was compared to that in mormal mice. No difference was found. Taken in conjunction with previous studies using labelling indices, the results indicate that in mice showing acute granulocytic hyperplasia, there is only a moderate increase in proliferation of mitotable granulocytes. Thus the major factor responsible for hyperplasia is increased differentiation of precursor cells.

Proliferative Responses of Mouse Mammary Glands to 17&lt;italic&gt;β&lt;/italic&gt;-Estradiol and Progesterone and Modification by Mouse Mammary Tumor Virus

The responses of mammary glands of ovariectomized mice to 17 beta-estradiol and progesterone were measured by mitotic and [3H]thymidine-labeled indices in low-tumor C57BL mice and high-tumor BR6 mice. The BR6 mice were subdivided into those carrying murine mammary tumor virus (MuMTV) and those that had been freed from it by foster nursing. In all groups, continuous stimulation by the two hormones administered together resulted in a cell proliferation peak. The magnitude of response varied according to strain and the presence or absence of MuMTV. The maximal effect was seen in BR6 mice carrying the virus. Comparison of percentage of labeled mitoses curves showed that the duration of DNA synthesis was extended in BR6 mice with MuMTV, although not sufficiently to account for the observed differences in labeling indices. The responses to 17 beta-estradiol and progesterone administered separately also varied. Mice carrying the virus were more susceptible to stimulation by progesterone, whereas those without the virus responded more to 17 beta-estradiol. The results suggested that the proliferative response of the mouse mammary gland to ovarian hormones can be modified by mammary tumor virus infection.

Chronic lymphocytic leukemia: A proliferative or accumulative disorder?

In two untreated patients with progressive CLL, quantitative 14C autoradiography of lymph nodes and, subsequently, continuous infusion of [ 3H] thymidine over eight and nine days, respectively, were performed in order to analyse the lymph node cell kinetics. Simultaneously, the turnover of labelled lymphocytes in the peripheral blood was evaluated. From another CLL patient a regional lymph node was removed 6 h after an intralymphatic flash injection of [ 3H] thymidine and sectioned for autoradiographic study of the distribution of labelled cells within the lymph node tissue. While the durations of DNA synthesis were found to be normal, the labelling indices were reduced. The relative cell production rate was far lower than normal. Very small growth fractions were calculated, amounting to less than 1% in one patient, and to 2.4% in the other. The distribution of labelled cells in the lymph nodes was focal, which supports the finding of low growth fractions. According to the present data, CLL is a disorder in which a very small number of cells cycle at a roughly normal rate. A kinetic definition of accumulative and proliferative tumour growth is introduced. Tumour growth is termed accumulative if growth appears to result from a decreased relative cell loss rate rather than an increased relative cell production rate. According to this definition, the kinetics in CLL may be classified as accumulative. In absolute terms, however, the number of lymphoid cells produced per unit of time was found to be far higher in CLL than in the healthy state.

Electron microscopic autoradiographic studies on dynamics and location of DNA synthesis of duck plague virus.

Electron microscopic autoradiographic studies on the dynamics and location of DNA synthesis by means of incorporation of 8H-thymidine during the replication of duck plague virus (DPV) revealed that the duration of DNA synthesis of DPV was rather long. The replication of viral DNA occurred simultaneously with the assembly procedure of nucleocapsids, the maturation and release of viruses. DNA synthesis of DPV occurred in the matrix with lower electron density in the nucleus. The replicated viral DNA accumulated in the viroplast with high electron density where the assembly of nucleocapsids occurred. The viroplast with high electron density was not the region of viral DNA synthesis.

Proliferation kinetics of malignant non-Hodgkin's lymphomas related to histopathology of lymph node biopsies.

Since lymphomas of high and low malignancy have been differentiated by the Kiel-classification, the cell kinetics of malignant lymphomas have become an interesting subject. In 20 non-Hodgkin's lymphomas we have determined the initial labelling index, the mitosis index, the proliferation rate and the durations of DNA-synthesis and mitosis. The kinetic variables have been estimated by using an in vitro-incubation of fresh biopsies and double-labelling with radioactive DNA-precursors. in 8 lymphomas of low malignancy we found an initial labelling index of 7.8%, a mitosis index of 0.3% and a potential tumour doubling time of 100.2 h for a cell production rate without regard to cell loss. On the other hand, lymphomas of high malignancy showed a labelling index of 16.7%, a mitosis index of 0.7% and a potential tumour doubling time of 40.5 h. All these values could be differentiated with high statistical confidence. DNA-synthesis time and mitosis time of both lymphoma groups did not show any significant differences. From these findings we obtained confirmation of the cyto-morphological principles used in classifying lymphomas.

The effects of dexamethasone on the cell kinetics of a murine malignant lymphoma.

The effects of dexamethasone on the cell kinetics of a rapidly growing syngeneic B cell malignant lymphoma in Balb/c mice have been studied. Growth curves, stathmokinetic studies and frequency of labelled mitoses (FLM) experiments were performed in groups of dexamethasone treated and control animals. These studies showed that tumour growth was arrested after 8 days treatment at which time the tumour weights were approximately half those of control animals. Dexamethasone increased the duration of the cell cycle with a particular increase in the duration of DNA synthesis. The results indicated that the effect on tumour growth could be attributed to a reduction in the growth fraction.