Distribution and specific activities of RNAs in isolated adipose cells with relation to exogenous lipids

Abstract

Several observations suggested that the rate of adipose cell formation is influenced by the fatty acid composition of the dietary fat: morphological studies, counting of cells, nuclear and mitochondrial DNA specific activities (SA). Therefore adipose cell RNAs were fractionated in an attempt to localize the site of this increased activity. Weanling rats were fed a diet containing 20% of sunflower oil (SO) or lard (L) for 21 days and fasted for 18 hr. They were then injected with either (6-¹⁴C) orotic acid or³²P-phosphate and killed 210 min or 18 hr later. The adipose cell ribosomal and nuclear RNAs were extracted and fractionated by ultracentrifugation in a sucrose gradient. Comparison of the SA of the fractions revealed that: (1) after 210 min of incorporation, ribosomal RNAs were more active in cells from rats fed SO; after 18 hr, nuclear RNAs of these cells were more active; (2) in each extract, 18S RNAs were always more active in SO than in L; (3) in the cells from the rats fed SO, at the nuclear level the synthesis of rapidly labeled heterodisperse RNAs seemed accelerated; at the ribosomal level they seemed to be utilized more rapidly. This is interpreted as indicative of stimulated enzymic induction.