RNA biosynthesis in adipose tissue: effect of fasting.

RNA metabolism has been examined in intact adipose tissue and isolated fat cells from rats. The lipocyte contains three species of RNA with sedimentation rates corresponding to those of ribosomal and transfer RNA. The de novo biosynthesis of RNA by adipose tissue cells in vitro was demonstrated. The base ratios of the RNA formed indicate that it was synthesized from a DNA template. Actinomycin D administered in vivo and in vitro decreased total RNA synthesis with the most marked effect on the synthesis of the heavy RNA components. Actinomycin D or puromycin added in vitro was not toxic: they did not inhibit total fatty acid biosynthesis or glucose utilization by the fat pad nor did they inhibit the immediate stimulation of fatty acid biosynthesis and glucose uptake by the addition of insulin in vitro. Starvation for 48-72 hr significantly depressed the synthesis of the heavy RNA components as measured by in vitro uridine incorporation into the individual RNA classes. Refeeding the fasted rat with glucose repaired the defect in RNA biosynthesis before the biosynthesis of monoenoic fatty acid was completely restored. Actinomycin D administered at the time of refeeding prevented the repair of monoenoic fatty acid synthesis. It is concluded that RNA metabolism is intimately involved in the control of biosynthetic reactions in adipose tissue.