Effects of rat epidermal chalone on uptake of thymidine, uridine, sorbitol and water by rat epidermis

A water soluble, endogenous substance (chalone) has been isolated from animal tissues in the past decade which has been shown to have mitotic depressant properties. This substance is further claimed to be tissue specific but not species specific. The present investigation was conducted to determine the effect of chalone on epidermal uptake of tritiated thymidine and tritiated uridine as an indirect index of DNA and RNA synthesis respectively. Additionally, studies were conducted to determine the effect of chalone, if any, on the extracellular fluid volume and cell membrane permeability using sorbitol C and tritiated water respectively. A chalone solution was prepared from rat epidermis by homogenization in aqueous buffer, pH 7.0. A portion of this solution was heated in an attempt to inactivate the chalone. Slices of epidermis taken by dermatome sectioning were incubated with either active chalone extract, heated chalone extract, or Bullough's Solution. In the thymidine and uridine uptake studies, epidermal sections were also treated with known inhibitors of DNA and RNA synthesis, cytosine arabinoside and actinomycin D respectively. These sections so treated were incubated for 15, 30, 45, 60, 90 and 120 minutes in each of the studies. After incubation, the epidermal slices were solubilized for counting in a liquid scintillation counter, and results were expressed both as disintegrations per minute per milligram of wet tissue weight and disintegrations per minute per milligram of protein. The results showed that chalone treated epidermis had less tritiated thymidine and uridine uptake at all incubation time periods than did epidermis treated with the Bullough's Solution, suggesting that chalone reduced mitosis by way of depressed nucleic acid synthesis. The chalone appeared to have no effect on the extracellular space or cell membrane permeability as there were no significant differences in sorbitol or tritiated water uptake at any of the incubation time periods.