Determination of Lymphocyte Turnover by Continuous Infusion of H³ Thymidine

The use of an osmotic pump for continuous infusion of H³ thymidine in rats is described. Estimates of turnover times of cells in the peripheral blood are 4 days for granulocytes, 60 days for large lymphocytes and in excess of 100 days for small lymphocytes. These turnover times include initial delay in release or maturation after the last mitosis in the marrow or nodes, and any time spent outside the circulation prior to final disappearance of a given cell from the peripheral blood. The data exclude reutilization as an explanation for the observed longevity of lymphocytes.