The effect of the epidermal G2 chalone on the mitotic duration in nude mouse epidermis and in a transplanted squamous cell carcinoma.

Balb/c/nu nude mice transplanted with a moderately differentiated squamous cell carcinoma were injected intraperitoneally with different doses of aqueous skin extracts containing the epidermal G2 chalone. The mitotic counts and the mitotic rates were determined in histological sections using a stathmokinetic method with vinblastine sulphate. The mitotic duration was calculated from the mitotic rates and counts. Skin extracts containing epidermal G2 chalone increased the mitotic duration in the epidermis, and a similar trend was seen in the tumour. The higher the dose of chalone, the longer the mitotic duration tended to be. A straight line of best fit used to indicate the dose/response relationship was steeper for the epidermis than for the tumour. The study thus shows that the epidermal G2 chalone not only prevents epidermal cells from entering mitosis, it also prolongs the mitotic duration. Further, the results do not contradict the theory that tumour cells may be less sensitive to chalone than normal cells.