DNA synthesis in liver and kidney of young rats. Autoradiographic studies with 3H-thymidine

Abstract

Autoradiographic studies following a single i.p. injection of3H-thymidine were performed in liver and kidney parenchyma of new-born and young adult rats at different ages (1, 2, 4, 7, 12, 18, 24, 30, 60 and 120 days). In 1-day-old animals the tritium index (i.e. percentage of DNA synthesizing nuclei) of both organs is lower than in the rat embryo. From 1–4 days fluctuations occur, then the tritium index rises at 7 and 12 days. But now an exponential decrease is observed up to day 120. This depression and fluctuation of the tritium index probably depends on a postpartal functional transposition and especially in the liver on a structural transformation. The mean grain density in the labelled nuclei increases from 1 up to 24 days, which is likely connected with a very high amount of endogenous thymidine in new-born rats. From day 24 the mean grain density can be taken as a relative measure for the rate of DNA synthesis. The reduction in the rate of DNA synthesis from 24–120 days is explained as a consequence of the commutation from the rapid to the slow mode in cellular proliferation.