ULTRASTRUCTURAL DIFFERENTIATION OF BROWN ADIPOSE TISSUE IN RAT

The development of interscapular brown adipose tissue has been observed in rats from 6 days ante partum to some days after birth. The most obvious alterations prior to birth were increases in cell volume, triglycerides, and glycogen stores as well as considerable growth of the chondriome. There was a marked differentiation of mitochondrial structure, including the formation of large intramitochondrial dense granules. At birth there was a rapid decrease in amount of glycogen and temporarily a depletion of stored triglycerides, simultaneously with increased numbers of autophagic vacuoles. The large intramitochondrial dense granules disappeared and chondriome growth was rapid during this time. In the days after birth the chondriome volume in the cells appeared to increase still further, and the triglyceride droplet fractional volume in the tissue also continued to grow. Evidence for the hypothesis that capillary endothelial cells are a major type of stem cell for adipocytes in brown adipose tissue, is discussed. © 1969 Academic Press, Inc.