SELECTIVITY OF FATTY-ACID MOBILIZATION - A GENERAL METABOLIC FEATURE OF ADIPOSE-TISSUE

This study extends our earlier work (T. Raclot and R. Groscolas. J. Li pid Res. 34: 1515-1526, 1993), which showed that, under norepinephrine -stimulated Lipolysis, fatty acids of rat retroperitoneal fat-cells ar e selectively mobilized. The present study examines whether this selec tive mobilization of fatty acids 1) is based on their proportions in a dipose tissue, 2) is a metabolic feature common to all adipose tissues , and/or 3) depends on the lipolysis-stimulating agent. Rat fat cells with two markedly different fatty acid compositions were isolated from four white adipose tissues and treated with three lipolytic agents. F atty acid composition of in vitro released free fatty acids was compar ed with that of fat cell triacylglycerols, the ratio of percent in fre e fatty acid to percent in triacylglycerol being defined as the relati ve mobilization rate (RMR). The RMR of individual fatty acids was rela ted to their molecular structure. It increased exponentially with unsa turation for a given chain length and decreased with increasing chain length for a given unsaturation. The selectivity of fatty acid mobiliz ation was similar regardless of the fatty acid composition of adipose tissue, the tissue location, and the lipolytic agent used. Under condi tions of stimulated lipolysis, the selectivity of fatty acid mobilizat ion is therefore a general metabolic feature of adipose tissue. Fatty acids with 16-20 carbon atoms and 4 or 5 double bonds had the highest RMR (from 1.4 to > 5), whereas fatty acids with 20-22 carbon atoms and 0 or 1 double bond had the lowest RMR (from 0.3 to 0.7). For the-othe r fatty acids, RMR was close to unity. Accordingly, they were schemati cally classified as highly, weakly, and moderately mobilizable fatty a cids.