Comparison of multiple injections with continuous infusion of tritiated thymidine, and estimation of the cell cycle time.

Labelled nuclei were counted in stratified squamous epithelium in mice killed after 24 h intraperitoneal administration of tritiated thymidine to label cells synthesizing deoxyribonucleic acid. Multiple injections produced the same result as an infusion of tritiated thymidine given after 24 h infusion of saline, but infusion of tritiated thymidine alone produced a different result. Thus, cell proliferation was depressed during the first 24 h of continuous infusion but was normal during the second 24 h. Comparison of proliferation of the oesophageal epithelium at the level of the thyroid and at the level of the diaphragm showed no difference between the two. Comparison of male with female mice given 72-h infusions of tritiated thymidine showed that cell proliferation occurred at the same rate in both. The cell cycle time was estimated in the epithelium of the oesophagus and tongue by comparison of mice given a single injection with mice given multiple injections of tritiated thymidine.