Effect of normal and tumor factors on different phases of cell populationscycle

In the present experiments we studied the effect of extracts from intact li ver (LE), ES2 tumor extract (TE), plasmas from intact mice (PI), and from t umor bearing animals (PT) on different phases of hepatocytes and renocytes cell cycles. C3HS 28-day-old male mice, standardized for periodicity analys is, were injected at 16:00 hours and killed every 4 hours during a circadia n cycle at 20:00/04; 00:00/08; 04:00/12; 08:00/16; 12:00/20 and 16:00/24 (t ime of day/ hours post treatment). Colchicine (2 mu g/g) was injected 4 hou rs before killing them. Samples of livers and kidneys were processed for hi stology and mitotic index determinations. The results were expressed as col chicine arrested metaphases per 1000 nuclei. The TE, LE and PI had a promot ing effect on the mitotic activity of hepatocytes during the first 12 hours post treatment. During the subsequent 12 hours, not only these treatments but also the PI had an inhibiting effect on the mitotic activity of the sam e cell population. Also the TE and the PT had a promoting effect on the mit otic activity of the renocytes during the first 12 hours while the effect o f all treatments showed a clear inhibition of the mitotic activity studied during the last 12 hours. Taking into account the time elapsed between the injections and the measurements made in these light-dark synchronized anima ls, we conclude that the increase in mitotic index observed in those tissue s stemmed from a reinitiation of cell-cycle traverse in a subpopulation of G(2)-arrested, noncycling cells.