Histological, histometrical and fluoride electrode studies of the effects of fluoride on the mandibular condyles in growing newborn rats

The effects of fluoride on the mandibular condyles in growing newborn rats were studied by histological, histometrical and fluoride electrode methods. The layer of cartilage of the mandibular condyle in the animals administered 5, 15, 25 and 35 mg/kg of fluoride for 3 weeks displayed a significant increase in thickness when compared with that of the mandibular condyle in the control animals. The thickening of the cartilage layer was proportioned to the amounts of fluoride administered. The volumetric density of cancellous bone of the condyle in the animals administered 25 and 35 mg/kg of fluoride also increased significantly when compared with that of the condyle in the control animals. The trabeculae of cancellous bone of the condyle in these animals contained large amounts of osteoid. The cancellous bone of the condyle in the animals of the four fluoride groups showed a significantly higher fluoride concentration when compared with that of the condyle in the control animals. The fluoride concentration proportionally increased with the amounts of fluoride administered. The results of the present study indicate that the morphologic changes and the fluoride concentrations in the mandibular condyles of rats receiving fluoride were closely correlated with each other.     

Localization of CD44 (hyaluronan receptor) and hyaluronan in rat mandibular condyle.

CD44 is a multifunctional adhesion molecule that binds to hyaluronan (HA), type I collagen, and fibronectin. We investigated localization of CD44 and HA in mandibular condylar cartilage compared with the growth plate and the articular cartilage, to clarify the characteristics of chondrocytes. We also performed Western blotting using a lysate of mandibular condyle. In mandibular condyle, CD44-positive cells were seen in the surface region of the fibrous cell layer and in the proliferative cell layer. Western blotting revealed that the molecular weight of CD44 in condyle was 78 to 86 kD. Intense reactivity for HA was detected on the surface of the condyle and the lacunae of the hypertrophic cell layer. Moderate labeling was seen in cartilage matrix of the proliferative and maturative layer. Weak labeling was also seen in the fibrous cell layer. In growth plate and articular cartilage, HA was detected in all cell layers. However, chondrocytes of these cartilages did not exhibit reactivity for CD44. These results suggest that chondrocytes in the mandibular condylar cartilage differ in expression of CD44 from those in tibial growth plate and articular cartilage. Cell-matrix interaction between CD44 and HA may play an important role in the proliferation of chondrocytes in the mandibular condyle.     

Flow cytometric measurement of cell cycle kinetics in rat Walker-256 carcinoma following in vivo and in vitro pulse labelling with bromodeoxyuridine.

Flow cytometric measurements of total DNA content, cell cycle distribution, and bromodeoxyuridine (BrdUrd) uptake were made in rat Walker-256 carcinoma cells. After both in vivo and in vitro pulse labelling with BrdUrd, Walker-256 tumor cells were stained with propidium iodide (PI) to estimate the total DNA content and a monoclonal antibody against BrdUrd to estimate the relative amount of cells in S phase. BrdUrd-labelled single cell suspensions were harvested at different time intervals to determine the movement of these cells within the cell cycle. To increase BrdUrd uptake, fluorodeoxyuridine (FDU), a thymidine antagonist, was also applied in vivo and in vitro. The results indicated exponential growth characteristics for this tumor between days 5 and 8 after implantation. Tumor doubling times, derived from changes in tumor volume in vivo and from the increase in cell number in vitro were similar. The mean time for DNA synthesis was estimated from the relative movement of BrdUrd-labelled cells towards G2. The percent of cells labelled with BrdUrd and the DNA synthesis time were similar regardless of the mode of BrdUrd administration. This study demonstrates that BrdUrd labelling of rat Walker-256 carcinoma cells in vitro yields kinetic estimates of tumor proliferation during exponential growth similar to those with the administration of BrdUrd in the intact tumor-bearing rat.     

The effects of 5-bromodeoxyuridine on the growth and morphology of transformed rat liver cells

The effects of bromodeoxyuridine (BrdUrd) on the growth, morphology, and tumorigenicity of the spontaneously transformed rat liver cell line R72/3 were studied. These cells grow either in suspension or in a monolayer and are tumorigenic. In monolayer cultures, cells treated with low concentrations (2.5 μg/ml) of BrdUrd were larger, more spread out, and more firmly attached to the substratum than were untreated controls. Treated cells failed to grow in suspension or on confluent monolayers of 3T3 cells and did not form colonies in soft agar. Scanning electron microscopy revealed extensive flattening of treated cells and a dramatic reduction in the number of microvilli on the cell surface. Transmission electron microscopy showed an increase in polyribosomes and rough endoplasmic reticulum, as well as an enlargement of endoplasmic reticulum cisternae and a complete absence of the bundles of intermediate size filaments that were conspicuous in untreated cells. The persistence of these changes required the continuous presence of BrdUrd in the medium. The effects of BrdUrd were readily reversed by withdrawal of BrdUrd and were not expressed in the presence of excess thymidine.     

Treatment of Mandibular Condyle Fractures Using a Modified Transparotid Approach via the Parotid Mini-Incision: Experience with 31 Cases

Surgery for mandibular condyle fractures must allow direct vision of the fracture, reduce surgical trauma and achieve reduction and fixation while avoiding facial nerve injury. This prospective study was conducted to introduce a new surgical approach for open reduction and internal fixation of mandibular condyle fractures using a modified transparotid approach via the parotid mini-incision, and surgical outcomes were evaluated. The modified transparotid approach via the parotid mini-incision was applied and rigid internal fixation using a small titanium plate was carried out for 36 mandibular condyle fractures in 31 cases. Postoperative follow-up of patients ranged from 3 to 26 months; in the first 3 months after surgery, outcomes for all patients were analyzed by evaluating the degree of mouth opening, occlusal relationship, facial nerve function and results of imaging studies. The occlusal relationships were excellent in all patients and none had symptoms of intraoperative ipsilateral facial nerve injury. The mean degree of mouth opening was 4.0 (maximum 4.8 cm, minimum 3.0 cm). No mandibular deviations were noted in any patient during mouth opening. CT showed complete anatomical reduction of the mandibular condyle fracture in all patients. The modified transparotid approach via the smaller, easily concealed parotid mini-incision is minimally invasive and achieves anatomical reduction and rigid internal fixation with a simplified procedure that directly exposes the fracture site. Study results showed that this procedure is safe and feasible for treating mandibular condyle fracture, and offers a short operative path, protection of the facial nerve and satisfactory aesthetic outcomes.     

A model of temporomandibular joint function in anthropoid primates based on condylar movements during mastication

The hypothesis that the shape of the bony temporomandibular joint (TMJ) is functionally related to sagittal sliding of the condyle during mastication is tested, and a model of the relation of sagittal sliding to mandibular size, TMJ shape, and diet is developed. Sagittal sliding is defined as fore-aft motion of the condyle during mandibular translation and/or angular rotation. Ascending ramus height is used as a structural correlate of the distance between the condyle and the mandibular axis of rotation (CR). Cineradiographic data on sagittal sliding and gape during mastication in Ateles spp., Macaca fascicularis, Papio anubis, and Pan troglodytes in conjunction with comparative data on mandibular size and TMJ shape are used to evaluate the hypothesis. The results show that 1) linear and angular gape are highly positively correlated with sagittal sliding, 2) pure mandibular translation is rare during mastication, 3) the CR is rarely if ever located at the condyle during mastication, 4) angular gape should be standardized in interindividual comparisons of sagittal sliding, and 5) the height of the ascending ramus (and by inference the CR-to-condyle distance) is highly positively correlated with absolute sagittal sliding. Sagittal sliding relative to the length of the articular eminence was the variable used to explore the relation between TMJ shape and sliding. This variable standardized absolute sagittal sliding relative to joint size. The relative depth and orientation of the articular eminence were not correlated with relative sagittal sliding. The anteroposterior curvature of the condyle was highly negatively correlated with relative sagittal sliding. Flat condyles are associated with large amounts of relative sagittal sliding. A flat condyle increases joint contact area, which reduces joint stress. A flat condyle also increases joint congruence, and this may facilitate the combined sliding and rolling motion of the condyle when the sliding motion is relatively large. The shape of the entoglenoid process was also positively correlated with relative sagittal sliding. A relatively large entoglenoid process may help to guide sagittal sliding and prevent excessive mediolateral sliding of the condyle. The functional model makes a number of predictions about the correlations between food consistency and food object size, mandibular size, TMJ shape, and sagittal sliding of the condyle during mastication and incision. Am J Phys Anthropol 109:67–88, 1999. © 1999 Wiley-Liss, Inc.     

Role of Articular Disc in Condylar Regeneration of the Mandible

The articular disc in the temporomandibular joint plays an important role in mandibular growth. Functional appliances induce regeneration of the condyle even after condylectomy. The aim of this study was to examine the role of the articular disc in regeneration of the condyle after unilateral condylectomy with use of a functional appliance in growing rats. Fifty growing rats were subjected to unilateral condylectomy and then half of them underwent discectomy. The functional appliance was applied to half of the rats in each group to induce regeneration of the condyle. Four and eight weeks later, morphometric and histologic analyses of the mandible were performed. Regeneration of the condyle was demonstrated in the two condylectomy groups. In the condylectomy+appliance group, the shape and cartilage of the condyle were equivalent to a normal condyle. However, regeneration of the condyle was not observed in the two discectomy groups even with the use of the functional appliance. The articular disc appears to be crucial in the regeneration of a damaged condyle, suggesting that defects or damage to the articular disc may influence mandibular growth and regeneration or repair of the condyle.     

Histochemical study of matrical components in the mandibular condyle of the neonatal mouse

In the mandibular condyle of the newborn mouse the chondroprogenitor (CP) zone is the only layer that incorporates 3H-thymidine thus serving the source for cells of the cartilage lineage. Ultrastructurally these cells have a mesenchymal appearance surrounded by collagen fibrils as well as by additional filaments that become apparent following fixation with ferrocyanide-reduced OsO4. In addition, electron-dense particles indicative of proteoglycans are scattered throughout the matrix in the CP zone as well as in the chondroblastic and hypertrophic zones. Following labeling with 35S-sulfate the CP zone as well as the other compartments revealed a substantial number of grains following processing for autoradiography. The number of grains per cell was highest in the hypertrophic zone. Indirect immunofluorescence indicated the presence of fibronectin in the articular surface, CP zone and in the hypertrophic zone. The immunogold method localized fibronectin intracellularly in CP cells and extracellularly in the hypertrophic zone. Therefore, in the mandibular condyle the CP cells which are capable for DNA synthesis are also involved in the synthesis of macromolecules of which some are specific for the cartilage phenotype, while others are associated with other functions of connective tissue cells.     

Development of a measurement system for the mechanical load of functional appliances

Devices called functional appliances are commonly used in orthodontics for treating maxillary protrusion. These devices mechanically force the mandible forward to apply traction force to the mandibular condyle. This promotes cartilaginous growth in the small mandible. However, no studies have clarified how much traction force is applied to the mandibular condyle. Moreover, it remains unknown as to how anatomical characteristics affect this traction force. Therefore, in this study, we developed a device for measuring the amount of force generated while individual patients wore functional appliances, and we investigated the relationship between forces with structures surrounding the mandibular condyle. We compared traction force values with cone-beam computed tomography image data in eight subjects. The functional appliance resulted in a traction force of 339–1477 gf/mm, with a mean value of 196.5 gf/mm for the elastic modulus of the mandible. A comparison with cone-beam computed tomography image data suggested that the mandibular traction force was affected by the mandibular condyle and shape of the articular eminence. This method can contribute to discovering efficient treatment techniques more suited to individual patients.     

Disparate effects of 5-bromodeoxyuridine on sister-chromatid exchanges and chromosomal aberrations in Bloom syndrome fibroblasts

The existence of a high frequency of spontaneous sister-chromatid exchanges (SCEs) in Bloom syndrome (BS) has thus far been supported by data on a small number of BS cell lines. To examine the cause of baseline SCEs more broadly, the frequencies of SCEs, as well as chromosomal aberrations (CAs) in 4 additional BS fibroblast strains were compared, under different assay and cell culture conditions, with those of normal cells in the range of approximately 0.9-90% 5-bromodeoxyuridine (BrdUrd) substitution into template DNA. SCEs at low levels of BrdUrd substitution were detected by an extremely sensitive immunofluorescent technique. From approximately 0.9% to 4.5% BrdUrd substitution, the SCE frequency in BS cells remained constant, at a level (40/cell) 8 times higher than that of normal cells. As BrdUrd substitution increased further, the SCE frequency in BS cells increased almost linearly, reaching 70-100 per cell at approximately 90% substitution, while the SCE increment in control fibroblasts was less than 5 per cell. Analysis of SCEs in 3 successive replication cycles similarly revealed that the SCE increment in BS cells depended on BrdUrd only at a high BrdUrd substitution level. In contrast to data on SCEs, CA induction by incorporated BrdUrd in BS cells was only slightly higher than that in normal cells. Thus, BS cells are extremely sensitive to BrdUrd for SCE induction, but much less so for CA induction.     

Ki-67 expression and BrdUrd incorporation as markers of proliferative activity in human prostate tumour models

Abstract. The validity of the use of the monoclonal antibodies Ki-67 and anti-BrdUrd to evaluate proliferative activity of human prostate tumour models was studied. Growth of the transplantable PC-82 and PC-EW prostate tumours, as assessed by tumour volume measurements, was significantly correlated with the proliferative activity as reflected by BrdUrd incorporation into DNA ( r = 0.64 and r = 0.78, respectively). The proliferative activity of PC-82 tumours detected by Ki-67 antigen expression paralleled the pattern observed with BrdUrd ( r = 0.51) and a significant correlation ( r = 0.60) between the results obtained with both markers was found. In growing PC-82 and PC-EW tumours only small variations in the Ki-67 and BrdUrd indices were observed. In contrast, Ki-67 expression in regressing PC-82 tumours varied considerably (2.7 ± 2.2%). The BrdUrd index in regressing PC-32 tumours showed less variation (1.3 ± 0.2%), but part of the BrdUrd-positive cells were found in the stromal (murine) part of the regressing tissue. It is concluded that the Ki-67 and BrdUrd proliferation markers are reliable parameters to monitor changes in growth of prostate tumour lines, but that in slow growing or regressing tumours Ki-67 and BrdUrd data should be interpreted with caution.     

Collagen I and II mRNA distribution in the rat temporomandibular joint region during growth

The distribution of type I and II collagen synthesis in the temporomandibular joint (TMJ) area of 1- to 28-day-old rats was studied after hybridization with probes to pro alpha1(I) and pro alpha1(II) collagen mRNA, and stain intensity through the various cartilaginous zones of the mandibular condyle and other areas of TMJ was assessed. The pro alpha(I) collagen mRNA was detected in the perichondrium/periosteum, in the fibrous and undifferentiated cell layers of the mandibular condyle, in the articular disc, and in all bone structures and muscles. The pro alpha1(II) collagen mRNA was found in the condylar cartilage and the articular fossa. Intensity in the condyle was highest in the chondroblastic layer and decreased towards the lower hypertrophic layer. In the condylar cartilage of the 21- to 28-day-old rats the chondroblastic cell zone was relatively narrow compared with the younger animals, whereas the reverse seems to be the case in the cartilage of the articular fossa. Changes in the pro alpha1(II) collagen mRNA were observed in the osseochondral junction area of the primary spongiosa, in that at the age of 5 days intense staining was found, whereas no staining was observed by 14 days. In the mineralizing zone, however, the majority of osteoblastic cells gave a positive signal with the pro alpha1(I) collagen probe. In conclusion, type II collagen synthesis of the mandibular condyle is restricted to its upper area. This differs from the long bone epiphyseal plate, where this type of collagen is produced virtually throughout the cartilage. Type II collagen synthesis of the fossal cartilage seems to increase as a function of age.     

A biomechanical analysis of mandibular scaling in old world monkeys

Scaling of mandibular dimensions in male Old World monkeys was investigated. Mandibular condyle length, width, and area were regressed separately against body mass and mandibular length for a total of 14 species of Cercopithecoids. Scaling of mandibular depth and width against both body mass and mandibular length were also investigated. When results of regression analysis using the two different independent variables (body mass and mandibular length) were compared, there were significant pattern differences in scaling of cercopithecines versus colobines. Compared to body mass, male cercopithecines had relatively large mandibles (length, width, and depth) and also relatively large condyles (length, width, and area). However, compared to mandibular length, cercopithecines had relatively transversely thin and shallow mandibles and relatively narrow condyles. It is shown that a “biomechanical” interpretation of mandibular scaling patterns against body mass in Old World monkeys demonstrates only that cercopithecines have prognathic faces, an already well-known and well-documented condition. When the biomechanical effects of prognathic faces are controlled for (by scaling against mandibular length), it is shown that cercopithecines possess special adaptations in condyle length while colobines possess special adaptations in condyle width and mandibular depth and width. These results clearly demonstrate the importance of selecting a relevant reference variable in scaling studies where biomechanical interpretations are attempted.     

Remodeling of the temporomandibular joint following mandibular distraction osteogenesis in the transverse dimension

Transverse mandibular distraction osteogenesis involves moving the osteotomized segments of the mandible in either a varus or valgus direction. This maneuver allows for widening of the bigonial distance or for a lateral shift of an asymmetric mandibular midline. During this process, a significant amount of torque is placed on the mandibular condyles, because they act as the pivot point for the mandibular translation. Although standard linear distraction osteogenesis induces transient, reversible changes in the temporomandibular joint, it is not known what effect the varus and valgus stresses of transverse distraction have on the temporomandibular joint. We therefore designed a study to document the temporomandibular joint changes following various degrees of transverse distraction.Bilateral transverse mandibular distraction was performed on 10 adult, female mongrel dogs using an external, multiplanar mandibular distraction device. The distraction protocol was as follows: (1) complete osteotomy at the angle of the mandible, (2) 5-day latency period, (3) distraction rate of 1 mm/day, (4) rhythm of one turn per day, (5) linear activation 16 to 30 mm bilaterally, and (6) 8-week consolidation period. A variety of varus and valgus distraction vectors were applied to the mandible only after 10 mm of initial linear distraction had been achieved. Posteroanterior and lateral cephalograms were performed throughout the entire process. Pre-distraction and post-consolidation computed tomographic scans were also performed. Changes in mandibular conformation, axis of rotation, temporomandibular joint structure, and glenoid fossa changes were directly assessed by evaluating the postmortem craniofacial skeleton. The findings were compared with those of normal, age-matched mongrel dog skulls.Significant remodeling changes were observed in the temporomandibular joints of all animals involved in the study. The mandibular condyles demonstrated varying degrees of flattening and erosion at all contact points with the craniofacial skeleton. In some cases, the condyle became part of the distraction regenerate process and was hypertrophied in all dimensions. The condyles were frequently displaced out of the glenoid fossa, particularly on the side in the direction of varus distraction. When the latter occurred, a new fossa was created on the undersurface of the zygomatic arch. Varying degrees of mandibular rotation in the sagittal plane were also observed, which led to abnormal torquing of the condyles in the coronal plane, depending on whether the axis of rotation occurred primarily around the condyle or around the distraction regenerate zone.In conclusion, transverse mandibular distraction is an effective means of producing a varus or valgus shift in the gonion relative to the midsagittal plane. However, unlike linear or angular mandibular distraction, transverse distraction has a multitude of nontransient effects on the temporomandibular joint. Therefore it must be emphasized that in clinical practice, transverse distraction should be used cautiously. One must also be aware that such a maneuver in distraction can have negative effects on the temporomandibular joint.     

Bromodeoxyuridine/DNA analysis of replication in CHO cells after exposure to UV light

The effects of ultraviolet light on cellular DNA replication were evaluated in an asynchronous Chinese hamster ovary cell population. BrdUrd incorporation was measured asa function of cell-cycle position, using an antibody against bromodeoxyuridine (BrdUrd) and dual parameter flow cytometric analysis. After exposure to UV light, there was an immediate reduction ( 50%) of BrdUrd incorporation in S phase cells, with most of the cells of the population being affected to a similar degree. At 5 h after UV, a population of cells with increased BrdUrd appeared as cells that were in G1 phase at the time of irradiation entered S phase with apparently increased rates of DNA synthesis. For 8 h after UV exposure, incorporation of BrdUrd by the original S phase cells remained constant, whereas a significant portion of original G1 cells possessed rates of BrdUrd incorporation surpassing even those of control cells. Maturation rates of DNA synthesized immediately before or after exposure by alkaline elution, were similar. Therefore, DNA synthesis measured in the short pulse by anti-BrdUrd fluorescence after exposure to UV light was representative of genomic replication. Anti-BrdUrd measurements after DNA damage provide quantitative and qualitative information of cellular rates of DNA synthesis especially in instances where perturbation of cell-cycle progression is a dominant feature of the damage. In this study, striking differences of subsequent DNA synthesis rates between cells in G1 or S phase at the time of exposure were revealed.     

Mechanism of formation of chromatid exchanges

Chinese hamster cells with different patterns of distribution of 5-bromodeoxyuridine (BrdUrd) between chromosome subunits were subjected, during the G2 stage, to UV irradiation, which only produced breaks in BrdUrd substituted DNA. The frequency of chromatid and subchromatid interchanges as well as isochromatid aberrations was estimated. It was found that only BrdUrd containing chromatids were involved into aberrations; this result challenges the so called "molecular theory" for aberration production proposed by Leenhouts and Chadwick. A very small increase of the aberration yield in chromosomes without BrdUrd may be connected with the action of UV on the frequency of recombination. The observed frequency of interchanges was not proportional to the BrdUrd content in chromosomes and depended on the time of its incorporation: more exchanges were induced in the chromatids incorporating BrdUrd during the last round of replication. These regularities may be connected with some molecular peculiarities of chromosome structure and function.     

Detection of cytosine arabinoside resistant cells at low frequency using the bromodeoxyuridine/DNA assay

This report describes a rapid and sensitive procedure for detection of cytosine arabinoside- (Ara-C) resistant mouse leukemia cells (L1210) in a predominantly Ara-C-sensitive population. L1210 cell lines sensitive or resistant to Ara-C were grown and treated with Ara-C in vitro or in vivo. Ara-C-resistant cells were detected as those cells with S-phase DNA content retaining the ability to incorporate bromodeoxyuridine (BrdUrd) after treatment with Ara-C. The BrdUrd incorporation ability of the S-phase cells was assessed by simultaneous flow cytometric measurement of cellular DNA content and amount of incorporated BrdUrd. The proportion of Ara-C-resistant cells was accurately estimated at frequencies approaching 10(-3).     

5-Bromodeoxyuridine inhibition of differentiation. Kinetics of inhibition and reversal in myoblasts

This paper describes experiments on the kinetics of inhibition of muscle differentiation in vitro in the presence of 5-bromodeoxyuridine (BrdUrd) and the recovery phenomena that occur when such inhibited cells are permitted growth in normal medium. The studies consist of a quantitation of cell fusion in the presence of the analog and during recovery in its absence coupled with simultaneous studies on changes in buoyant density of cellular DNA. We find that if myoblasts are exposed to BrdUrd during the last doubling before cell fusion would normally occur, most cells do not differentiate, but as many as 18% of the cells can fuse in spite of the incorporation of BrdUrd into their nuclei. These nuclei contain approximately the amount of BrdUrd expected for a full round of DNA synthesis. Studies on the rate of recovery of inhibition of cell fusion following one generation in BrdUrd reveal that after one doubling of inhibited cells in the presence of normal medium. fusion reaches about 50% of the control value; after two doublings it reaches 75% of control value; and after 2.5 doublings of reversal, recovery is essentially complete. We find that both the degree of inhibition after approximately one round of BrdUrd incorporation and the rate of cell differentiation after two generations of reversal are consistent with a model which assumes that BrdUrd “sensitivity” resides on single pair of chromosomes and that inhibition occurs in a dominant fashion if approximately 30% or more of the thymidine is replaced by BrdUrd in the readout strand of either chromosome.     

Dental abrasion as a factor in remodeling of the mandibular condyle.

Skulls of 100 male and female subjects of various ages and with unimpaired dental arches were examined with respect to the morphological features of the mandibular condyle. A certain number of typical shapes were distinguished. Dental abrasion was also assessed and three parameters were calculated: (1) total abrasion index; (2) working:balancing abrasion ratio, and (3) frontal abrasion index. These data were then related to condylar shape and subject age. The results show that abrasion influences changes in condyle shape due to bone remodeling. The forces applied on this bone segment are distributed over functional areas that vary both in extent and in their different characteristics.     

Cell cycle kinetic measurements in an irradiated rat rhabdomyosarcoma using a monoclonal antibody to bromodeoxyuridine

Cell cycle kinetics after X-irradiation were studied in a solid rat rhabdomyosarcoma using a monoclonal antibody to bromodeoxyuridine (BrdUrd) in cells in which the DNA was labeled by BrdUrd. It could be shown that this tumor was composed of about 80% diploid host cells, and only 20% of the cells in the dissociated tumor were actually tetraploid tumor cells. When rats were injected intraperitoneally with BrdUrd to label S-phase cells in the tumor, only a fraction of both types of cells became labeled with BrdUrd during S-phase, even 24 h after injection. The diploid BrdUrd-labeled cells progressed rapidly into cycle; 4 h after injection of BrdUrd, labeled diploid G1-phase cells could be observed. Only 25% of the tetraploid S-phase cells could be labeled by a single injection of BrdUrd (160 mg/kg body weight). These labeled tetraploid cells progressed through the cell cycle with similar velocities as did labeled diploid cells. Using a "Mini Osmotic Pump" containing bromodeoxycytidine (BrdCyd) at high concentration (0.3 mol/L) that released BrdCyd continuously into the organism where it was converted to BrdUrd, it could be shown that after 2 days about 60% of cells in S-phase and 70% of cells in G2-phase were labeled. The fraction of labeled G2-phase cells in irradiated tumors (D = 10 and 20 Gy) was enhanced between 10 and 50 h after irradiation due to a radiation-induced G2 block in cycling tetraploid tumor cells.(ABSTRACT TRUNCATED AT 250 WORDS)