Developmental changes of lipogenic enzyme activities and lipogenesis in brown adipose tissue and liver of the rat.

1. Brown adipose tissue (BAT) and liver lipogenesis in vivo estimated by using 3H2O as tracer was very low and did not change significantly between 10 and 20 days after birth. Lipogenesis increased dramatically in both tissues by weaning at 20 days, peaking between 25 and 30 days of age. Since that time the rate of fatty acid synthesis in BAT decreased gradually to reach adult level after 2 months, whereas in the liver there was a sharp decrease of lipogenesis. 2. The activities of fatty acid synthase, citrate cleavage enzyme, malic enzyme and glucose 6-phosphate dehydrogenase essentially followed a similar course of developmental changes as lipogenesis. 3. In contrast to the enzymes listed above NADP-linked isocitrate dehydrogenase remained unaltered over the period studied, whereas lactate and malate dehydrogenases exhibited very high activity at 10 days after birth and from then decreased to reach adult level at the age of about 20 days. 4. The data obtained indicate that no substantial differences could be detected in the developmental pattern of lipogenesis and lipogenic enzyme activities between BAT and liver up to 30 days of age but after this time these processes were not co-ordinated in both tissues. Beyond this time the BAT was characterized by a much higher rate of lipogenesis than the liver. 5. The results are discussed in terms of the nutrient changes and the relationship between thermogenesis and lipogenesis in BAT.