Fate of Intraintestinal Thymocytes Labeled with 125lododeoxyuridine or Tritiated Thymidine12

A suspension of thymocytes labeled with 125IUdR or 3HTdR was injected into the jejunum of mice. The bulk of the radioactivity disappeared within few hours from the intestine and was recovered principally in the urine. This indicated a very rapid breakdown of labeled thymic cells, reabsorption and subsequent elimination of the tracer in the kidney. In mice injected with cells labeled with 3HTdR, the initial rapid loss of radioactivity was of shorter duration, and slower during the second phase, presumably due to more extensive reutilization and/or prolonged persistence of acid-soluble radioactivity. Pretreatment of the recipients with antibiotics did not significantly reduce the rate of radioactivity loss.