Mitotic activity in fetal and early postnatal porcine adipose tissue

Tritiated thymidine autoradiography and histochemistry were used to study the development of subcutaneous adipose tissue of lean and obese fetuses and postnatal pigs. A pattern of tritiated thymidine uptake by pre-adipocytes and adipocyte lipid accumulation was demonstrated during the growth of the fetal pig. In the youngest fetuses there was a period of intense stromal cell mitotic activity before any adipocyte lipid accumulation. During subsequent fetal development, clusters of tightly arranged stromal cells were formed. Lipid accumulation occurred only in these cell clusters. During this time of cell cluster formation and lipid accumulation, mitotic activity was minimal. In obese fetuses, stromal cell mitotic activity overlapped temporarily with the cell cluster formation and lipid accumulation period. In early postnatal pigs, fat cell clusters increased in size until they "physically filled" the adipose tissue. In pigs 3 d and older, there was extensive mitotic activity of cells within the fat cell clusters. The synthesis of this second bed of pre-adipocytes and the altered developmental pattern in the obese fetuses is suggested to be due to the influence of a high fat diet. The significance of these findings in terms of plausible links between pre-adipocyte mitosis and lipid accumulation is discussed.