Recovery kinetics of epidermal cell proliferation after two intraperitoneal injections of epidermal extracts (chalone).

The cell kinetic effect of two intraperitoneal (IP) injections of 5 mg of crude lyophilized skin extracts given 12 h apart was assessed during the recovery period (5 to 52 h after last injection) by measuring epidermal labelling indices and the specific activity after tritiated thymidine (3HTdR) injection, and by determining the cell cycle phase distribution by flow cytometry. The skin extracts produced an epidermal chalone effect and inhibited both DNA synthesis and mitosis. A slow recovery took place from 5 to between 22 and 36 h after the last chalone injection. During this period the cell flux into DNA-synthesis and mitosis slowly recovered, but the exits were blocked and cells accumulated in the respective phases. The fluxes out opened up at the S phase about 22 h, and at the M phase about 30 h after the second chalone injection. A secondary inhibitory effect was observed at about 40 h, followed by a subsequent recovery to normal at 52 h. The similarity between the recovery kinetics after chalone and that observed after hydroxyurea (HU) is emphasised.