Studies on cell proliferation in inguinal adipose tissue during early development in the rat.

[2-14C] Thymidine was injected into rats aged 3,5 and 10 days, and incorporation of the precursor into deoxyribonucleic acid (DNA) of the inguinal fat tissue was measured for short time periods. Using chromatographic procedures to measure the distribution of thymidine and its metabolites in the soluble fraction of the tissue, degradation of the precursor was found to be similar at all ages. The data indicate that thymidine was more rapidly utilized for DNA synthesis in 3-day-old rats than in older animals. When 14C-thymidine was injected in vivo and adipocytes and stromal cells were then separated from the inguinal tissue of 3-and 5-day-old rats, the incorporation into DNA was significant in both types of cells already 30 min after pulse labeling. Stromal cells took up twice as much of label as the adipocytes. Furthermore, real incorporation into DNA was found in the adipocytes when incubated in vitro in a culture medium supplemented with 14C-thymidine. The possibility is discussed that early in postnatal life adipocytes might synthesize DNA for further cell division.