The contribution of lipogenesis in situ to the accumulation of fat by rat adipose tissue

The purpose of this study was to assess the contribution of lipogenesis in situ for the accumulation of fat by the adipose tissue of rats. [U-¹⁴C] Glucose was injected into animals that had been fed diets containing increasing amounts of corn oil. Under these conditions the recovery of labelled fatty acids from the adipose tissue of the animals fed diets containing 4 and 9% corn oil was significantly decreased. On the other hand, when the adipose tissue of these animals was incubated in vitro in the presence of [U-¹⁴C] glucose, the synthesis of labelled fatty acids was significantly increased. Increasing amounts of dietary fat did not alter the adipose tissue lipoprotein lipase activity. Under these conditions the uptake of labelled triglyceride fatty acids by the adipocytes of rats fed fat is probably very limited when compared with the uptake by the adipocytes of rats fed on a fat-free diet. In the liver of the animals fed fat the synthesis of labelled fatty acids was decreased both in vitro and in vivo. By reducing the in vivo lipogenesis by the liver the amount of labelled triglyceride fatty acids of hepatic origin secreted into the plasma was also reduced. It is argued, therefore, that in the animals fed on a fat-free diet the radioactivity recovered in the adipose tissue fatty acid fraction can probably be credited to synthesis in situ and uptake of plasma triglyceride fatty acids, while in the adipose tissue of the animals fed on a high-fat diet the radioactive fatty acids recovered in the adipose tissue can be credited mainly to synthesis in situ.