Circadian biological time influences the effect adriamycin has on DNA synthesis in mouse bone marrow, ileum and tongue but not Ehrlich ascites carcinoma.

Adriamycin (ADR; 10 mg/kg) was given to mice bearing a 5-day-old Ehrlich ascites carcinoma (EAC) at two different circadian times: 05.00 and 17.00 h. The incorporation of tritiated thymidine into DNA (DNA synthetic activity; DNA-SA) was studied in the epithelium of the tongue, ileum, bone marrow and the EAC over a 120-hour period after treatment. ADR at 05.00 h was more perturbing of DNA-SA in the normal organs than was ADR at 17.00 h. ADR at 05.00 h caused greater inhibition of DNA-SA for longer periods of time than did ADR at 17.00 h. Thus, the point in the circadian system of the host when ADR was given significantly affected the result obtained in the normal organs. This was not true for the EAC. DNA-SA in the EAC responded in an almost identical manner regardless of whether the ADR was given at 05.00 or at 17.00 h.