[Analysis of the depression of the mitotic activity of the corneal epithelium in white rats under chronic pyrogenal stress].

It was established previously that stable depression of cell division in corneal epithelium under chronic stress is not related to variations in the index of labeled nucleus (ILN). The paper demonstrates that five-day long pyrogenal injection did not alter the daily ILN: it was 67% in control rats and 69.7% in the experimental group. Cytophotometric logical sections showed that chronic stress led to a significant increase in the number of tetraploid nuclei (from 3.2 to 7.7%). No material changes were observed in the content of nuclei belonging to other classes. No polyploidization or G(2) growth evidence were recorded either. The absence of progressive rise in tetraploid nuclei and of more pronounced polyploidization in the presence of long-term depression of the cell cycle and stable ILN is explained by circadian variations in the mitotic activity reaction to stress. During chronic stress the depression of the cell cycle observed in the day and evening time was not recorded in the morning hours at the height of the mitotic activity. This circadian shunt is conducive to maintaining modal ploidity of corneal nuclei.