Development of perirenal adipose tissue in the neonatal lamb: effects of dietary safflower oil.

Perirenal adipose tissue development was investigated in lambs from birth until 17 days of age. Changes in the morphology, the lipid, protein, RNA and DNA content, the adipocyte number and size, and the rate of protein, RNA and DNA synthesis of the perirenal fat-pads are reported. During the first 9 days after birth the tissue lost the morphological characteristics of brown adipose tissue and acquired those of white adipose tissue. As there was no change in either the number of adipocytes or the DNA content of the fat-pads between birth and 9 days of age it is concluded that there was a differentiation of brown into white adipocytes. Over 80% of the increase in tissue weight between birth and 17 days of age was due to lipid deposition. Administration of safflower oil to the lambs had no apparent effect on the change from brown to white fat, but it markedly reduced the rate of lipid deposition between days 9 and 17 post partum.