Histoautoradiographical detection of DNA repair synthesis in different organs of mice after methylnitrosourea "in situ".

Methylnitrosourea (MNU) was applied by gavage into the stomach in a dose of 123.1 mg/kg. Hydroxyurea (250 mg/kg) and 6 (3)H thymidine (dTh - 2 MBq/g) were injected intraperitoneally. DNA repair synthesis as the labelling of non-proliferating cells was most reliably established in the testicles, bronchi, duodenum, kidney, liver and pancreas after 3 months to 3 years exposure of the histoautoradiograms. The findings in the stomach and rectum are near to this group. Less reliable positivity was found in the adrenals, urinary vesicle, spleen and heart, while in the musculature of the abdominal wall and in the thymus the results were negative. There is some correlation of these results with literary data about organ specific development of tumors after orally applied MNU to mice. This suggests wide applicability of this autoradiographical method. The possibility of increasing the dose of 3H thymidine is also discussed.