MITOTIC RATE IN THE EPIDERMIS OF WARM- AND COLD-ACCLIMATED RATS

Abstract

The effect of the environmental, temperature on the mitotic activity in the skin of warm- and cold-acclimated rats was estimated with the colchicine method. On rats kept at 30 °C for 3 months, the skin temperature was found to vary from 30.4 °C on the ear, to 35.3 °C on the back. Least-square linear relationships were established between log induction rate (rate at which cells start division), log mitotic duration, and tissue temperature. The colder the epithelium, the lower was the induction rate and the longer was the mitotic duration. Depending on their temperature, the different epithelia studied could be classified as far as their mitotic activity was concerned, in the following decreasing order: duodenum, back, tail, foot, and ear. For a 7 °C difference in temperature between duodenum and ear, there was a sevenfold difference in mitotic duration, which reveals an unusual Q₁₀ of 10.The data obtained on similar epithelial tissues of cold-acclimated rats supplied some evidence of adaptation in the mitotic rate of the back skin. In the ear, foot, and tail skin the colchicine method failed to give quantitative data because mitosis was proceeding too slowly. It even failed in rats maintained in the cold for 118 days. When this finding is considered together with the observations reported previously that after 3 weeks of cold exposure, mitotic activity in the ear is resumed, after having been stopped almost completely, it appears that the adaptation that has taken place in this cold tissue is one that allows the cells to overcome the mitotic blocking effect of cold but not one which allows mitosis to proceed at a much faster rate than would be indicated by the Q₁₀ observed on the epithelia of the "30 °C rats".