Growth fraction and cycle duration of hepatocytes in the three-week-old rat

The proliferation of hepatocytes in the liver of 3-week-old rats has been investigated by autoradiographic methods. This investigation is a continuation of earlier work on the same topic (Schultze & Maurer, 1972; 1973). 21 days after birth, 102 rats received a single injection of 3H-TdR. The percentage of labelled mitoses was then determined 1 hr later and at various times throughout the interval up to 12 days after application of 3H-TdR. In agreement with earlier work, a first peak of labelled mitoses was found 7 hr after 3H-TdR injection. The area under the peak indicates an S phase duration of 8 hr. In addition a second very broad peak of labelled mitoses was found between 2 and 12 days after pulse labelling. The analysis of the results leads to the conclusion that the hepatocytes of the 3-week-old rat have a growth fraction close to 1 and a doubling time of 6-7 days. This is at variance with earlier results of Post, Huang & Hoffman (1963) and Grisham (1969) who had derived a value of 21.5 hr for the duration of the cell cycle and a value of only 0.1-0.2 for the growth fraction of the hepatocytes.