In vivo synchronization of murine sarcoma 37 ascites tumor cells by use of hydroxyurea

Synchrony of DNA synthesis in mouse sarcoma 37 ascites cells was achieved in vivo by injection of 0.75 mg hydroxyurea per gram weight of mouse. DNA synthesis was gauged by comparing 3H-labeled thymidine incorporation, under defined conditions, to total DNA measured colorimetrically. DNA synthesis in the sarcoma 37 cells fell to negligible levels 4 hours after injection and remained at or below levels observed in randomly dividing cells up to 18 hours after injection. A sharp increase in DNA synthesis occurred at 20 hours, followed by a decline again at 22 hours after hydroxyurea injection. DNA synthesis in the intestine remained below control values at 20 hours.