SELECTIVE MOBILIZATION OF FATTY-ACIDS FROM WHITE FAT-CELLS - EVIDENCEFOR A RELATIONSHIP TO THE POLARITY OF TRIACYLGLYCEROLS

Fatty acids are selectively released from white fat cells in accordanc e with well-defined rules relating their molecular structure and their mobilization rate, emphasizing the possible role of their physicochem ical properties. Lipolysis is widely reported to work for conditions w here only small amounts of substrate are available. We hypothesize tha t the preferential hydrolysis of a substrate fraction enriched in the most polar triacylglycerols (TAGs) reflects the pattern of selective f atty acid mobilization. Rat adipose tissue was first manipulated by di etary means to obtain a wide spectrum of fatty acids, Fat cell TAGs we re separated into eight fractions according to polarity by liquid-liqu id partition chromatography and their fatty acid proportions and compo sitions were determined by GLC. In the most polar TAG fractions, the r elative enrichment of fatty acids (percentage in a TAG fraction divide d by percentage in total TAGs) increased with the number of double bon ds for a given chain length, whereas it decreased with increasing chai n length for a given degree of unsaturation. The relative enrichment o f highly mobilized fatty acids (16-20 carbon atoms and four or five do uble bonds) was very high (more than 2.5) in the most polar TAG fracti ons, whereas that of weakly mobilized fatty acids (20-24 carbon atoms and no or one double bond) was very low (less than 0.5). The relative enrichment of moderately mobilized fatty acids (comprising all the oth ers) was close to unity. Our study shows that the relative enrichment of fatty acids in the most polar adipose tissue TAGs is consistent wit h their relative mobilization rates. This supports our hypothesis and raises the possibility that the molecular species of TAGs might be one of the regulating factors.