Cell kinetics of mouse urinary bladder epithelium

A dose of 0.2 ml propylene glycol (1,2 propanediol) was injected subcutaneously into 12 hairless mice three times a week for three months. Four animals were killed at 1, 2 and 3 months and micro-flow fluorometric histograms of the bladder epithelial cells were made. The proportion of cells in diploid S phase was not much altered, but the proportion of tetraploid S-phase cells was significantly reduced and at three months DNA synthesis in tetraploid cells completely disappeared. The proportion of diploid cells increased, the proportion of tetraploids was slightly reduced and almost all octoploid cells disappeared. The changes are qualitatively similar to those seen after the bladder carcinogen dibutylnitrosamine, and after repeated injections of cyclophosphamide, but quantitatively much less pronounced. They can be explained as a result of cell toxicity whereby propylene glycol kills some bladder epithelial cells and disturbs the mechanism of repeated DNA synthesis. Propylene glycol is thus not a completely harmless solvent and when the kinetic effects of bladder carcinogens dissolved in propylene glycol are studied, the effect of the solvent alone must be accounted for.     

Cell kinetics of mouse urinary bladder epithelium. IV. Changes in cell proliferation, nuclear DNA content, and number of diploid, tetraploid and octoploid cells after a single dose of dibutylnitrosamine.

The initial effect of a single subcutaneous injection of 0.01 ml of dibutylnitrosamine on the mouse (hr/hr strain) urinary bladder epithelium was a block in DNA synthesis in the diploid cells followed by a regenerative reaction. This did not, however, lead to a subsequent wave of increased DNA synthesis among the tetraploid cells. Later, a new wave of DNA synthesis occurred among the diploid cells, and again there was no subsequent wave of tetraploid DNA synthesis. The total cell number was not affected. These disturbances resulted in periods of reduced numbers of octoploid cells. This effect was unlike that obtained in previously published experiments using cyclophosphamide, which led to considerable hyperplasia, especially of octoploid cells, and no disturbance of tetraploid DNA synthesis. Thus the action of a single dose of dibutylnitrosamine on the epithelial cells in the mouse urinary bladder is very different from that of cyclophosphamide in a single dose, but it is not possible to say whether this has anything to do with the carcinogenicity of the nitrosamine.     

Cell kinetics of mouse urinary bladder epithelium. III. A histologic and ultrastructural study of bladder epithelium during regeneration after a single dose of cyclophosphamide, with special reference to the mechanism by which polyploid cells are formed.

In order to see whether the polyploid cells lining the mouse urinary bladder are formed by nuclear fusion, such epithelium was studied under the light and electron microscope forty-eight hours after an injection of cyclophosphamide when the bladder epithelium regenerates with rapid formation of many diploid, tetraploid and octoploid cells. The probability of seing fusion, if it occurs, ought then to be high. Serial sections of many specimens from four mice revealed no signs of fusion. Thus we found no support for the theory that polyploid cells are formed by nuclear fusion.     

Cell cycle kinetics of regenerating urothelial cells of the rat urinary bladder after partial cystectomy

The cell cycle kinetics of bladder urothelial cells regenerating after partial cystectomy were investigated in 96 female Wistar rats using the percentage labelled mitoses method. In the area of resection a mean cell cycle time (TC) of 15 h was determined. The DNA synthesis phase (TS) lasted 6 h and the premitotic-postsynthetic phase together with the mitosis phase (TG2 + M) 1.5 h, thus giving a presynthetic-postmiotic phase (TG1) of 7.5 h. Similar values were found for the urothelial cells in the stump: the mean cycle time measured 14 h, the TS-phase 6 h, the TG6 + M-phase 2 h and the TG1-phase 6 h. These data are discussed with respect to known cell cycle parameters of bladder urothelium regenerating in response to cytotoxic agents and of neoplastic urothelial cells. The reported findings provide a basis for further investigations using weak carcinogens and threshold doses of potent carcinogens to test the working hypothesis that stimulation of proliferation following partial cystectomy is capable of initiating, accelerating and/or potentiating carcinogenic cell transformation in the urinary bladder.     

Cell population kinetics of the mouse lens epithelium

The dividing lens epithelium of 8-week-old CF1 mice consists of a monocellular layer of about 31,000 cells and does not include the postmitotic cells of the meridional rows and another postmitotic zone of seven cell positions' width immediately anterior to the rows. The latter two populations contain approximately 3,600 and 9,000 cells, respectively, for a total of 44,000 cells in the entire lens epithelium. Autoradiographic analysis based upon mitotic index and cell cycle times indicates that the epithelium produces 207 new lens fibers a day. Throughout the 20-day period of study, labeled cells appeared almost entirely as pairs following a single dose of ³H-thymidine and clusters of labeled nuclei were not seen. Moreover, the number of labeled cells dropped only slowly with time, as did the grain counts. These observations indicate that logarithmic division “cascade” does not occur in the lens. The dividing cell population consists largely of a slowly cycling stem cell group, dividing once about every 17–20 days, and consisting of some 5,000 cells. A subpopulation may exist which undergoes two rapid consecutive divisions before becoming postmitotic, but this is too small to make a significant contribution to lens fiber production. Four days are required to transit the postmitotic zone, and an additional 43 or so are needed to transit the meridional rows and differentiate into anucleate lens fibers. Data from other laboratories indicate that the entire process, from mitosis to final differentiation, requires about 4 months. Hence, most of this time is spent in migration of nondividing cells.     

Changes in the kinetics of rabbit thymus DNA re-association in various time periods after gamma-irradiation

A distinction has been detected in the kinetic curves of the control and in vivo irradiated DNA at the site of the reassociation of moderate and unique genome fractions. This distinction increased with increasing Cot. It was shown that the thermostability decreased and the profiles of DNA duplex thermoelution changed in irradiated rabbits as compared with intact ones.     

Renewal of the epithelium in the descending colon of the mouse. IV. Cell population kinetics of vacuolated-columnar and mucous cells.

Proliferation and migration of cells in the vacuolated-columnar and mucous cell lines were studied in the descending colon of adult female mice given a single injection or a continuous infusion of 3H-thymidine and killed at various intervals from one hour to 12 days. This investigation was carried out using one mum-thick Epon sections which were radioautographed after staining with the periodic acid-Schiff technique and iron-hematoxylin. In the normalized crypts with ten equal segments, labeled vacuolated cells at one hour after injection of 3H-thymidine were encountered in the lower four segments and in decreasing numbers in segments 5 through 7. From the percent labeled cells in segments of the crypt, the birth rate and fluxes of cells were computed. Moreover, it was found that a cell in the vacuolated-columnar cell line would undergo three mitotic cycles on the average from its birth at the cryptal base to its extrusion from the surface; of these three cycles, the last one which took place from segment 3 to segment 7 appeared to be a changeover from dividing cells to non-dividing cells, in accordance with the "slow cut-off" model of Cairnie et al. ('65b). Mucous cells located in segments 1 through 6 of the crypt were capable of incorporating 3H-thymidine and thus capable of undergoing mitosis. However, the rate of turnover of mucous cells based on proliferative rate was found to be much lower than the rate of turnover of mucous cells based on the transit time in the non-dividing segments of the crypt. Since there was a concomitant overproduction of cells in the vacuolated cells and newly formed mucous cells in the lower portion of the crypt, it was concluded that some vacuolated cells would give rise to mucous cells. This putative transformation occurred in the lower four segments of the crypt. Mucous cells which were formed by transformation would migrate upward along the cryptal wall and accumulate more mucus in the theca; in doing so, they would undergo two divisions, on the average, before they became non-dividing mucous cells. In ascending the cryptal walls, both vacuolated-columnar cells and mucous cells appeared to migrate at a similar speed; they moved much slower at the base of the crypt and accelerated toward the upper portion of the crypt, but they migrated at a constant speed in the non-dividing segments of the crypt.     

Cell kinetics in the mouse esophageal epithelium in relation to the time of day

The kinetics of mouse esophageal epithelial cells was investigated throughout 90 h after a single injection of 3H-thymidine at 01 or at 13 h--the times of the peak and minimal magnitudes of the radioisotope index in the circadian rhythm of proliferation. The mitotic cycle parameters in the cells varied but insignificantly. For cells treated with 3H-thymidine at 01 h, T = 24.3 h, ts = 6 h, tG2 min = 1.5 h, tG2+ 1/2 M = 2.9 h and tG1+/2 M = 15.4 h; for those treated with 3H-thymidine at 13 h, T = 25.6 h, ts = 8.4 h, tG2 min = 1 h, tG2+ 1/2 M = 2.2 h, tG1+ 1/2 M = 15 h. Cells labeled at 01 h proliferated more actively for a long period of time as compared to those labeled at 13 h. The synchronism in undergoing several successive mitotic cycles was greater for cells labeled at the peak radioisotope index. The data obtained also suggest that the majority of cells enter the G0 phase after the completion of the first cycle. The duration of the G0 phase varies in different cell populations.     

Frequency of micronucleated cells in the mouse bone marrow after exposure to various doses of gamma-radiation

The frequency of micronucleated cells was determined in the bone marrow of female BALB/c mice exposed to different doses of gamma-radiation at 1, 3, 10 and 14 days post irradiation. The frequency of micronucleated cells increased with the increase in exposure dose at all time period studied. However, the frequency of micronucleated cells declined with time irrespective of exposure dose. The dose-response curve thus obtained was linear.     

Cell kinetics of vocal fold epithelium in rats.

In order to investigate the kinetics of vocal fold epithelium a bromodeoxyuridine-anti bromodeoxyuridine method has been applied in vivo at both light and electron microscopy level. This method is able to define the length of both epithelium turnover and cell-cycle in basal elements, as well as the existence of a higher proliferation rate during night time in comparison with day time. Moreover distinct labeling patterns observed in incorporating cells allow us to define the precise localization in S-phase of cycling elements.