Selectivity of fatty acid mobilization: a general metabolic feature of adipose tissue

Abstract

This study extends our earlier work (T. Raclot and R. Groscolas. J. Lipid Res. 34: 1515-1526, 1993), which showed that, under norepinephrine-stimulated lipolysis, fatty acids of rat retroperitoneal fat cells are selectively mobilized. The present study examines whether this selective mobilization of fatty acids 1) is based on their proportions in adipose 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. Fatty acid composition of in vitro released free fatty acids was compared with that of fat cell triacylglycerols, the ratio of percent in free fatty acid to percent in triacylglycerol being defined as the relative mobilization rate (RMR). The RMR of individual fatty acids was related to their molecular structure. It increased exponentially with unsaturation for a given chain length and decreased with increasing chain length for a given unsaturation. The selectivity of fatty acid mobilization was similar regardless of the fatty acid composition of adipose tissue, the tissue location, and the lipolytic agent used. Under conditions of stimulated lipolysis, the selectivity of fatty acid mobilization 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 other fatty acids, RMR was close to unity.(ABSTRACT TRUNCATED AT 250 WORDS)

Fatty acid composition of blubber of the Baikal seal Phoca sibirica and its marine relative, the ringed seal P. hispida

“…In addition, experiments with laboratory rats suggest that continuous weight-cycling, that is especially likely to occur in the metabolically very active inner blubber, will increase the proportion of long-chain MUFA and SFA in adipose tissue triacylglycerols through the preferential hydrolysis of C16 and C18 MUFA and PUFA (Raclot et al 1995).…”

What Does the Measurement of Whole-Body Fatty Acid Rate of Appearance in Plasma by Using a Fatty Acid Tracer Really Mean?

“…This extrapolation assumes that the R a of the fatty acid being traced is representative of the release of other fatty acids from adipose tissue and that the relative concentration of this fatty acid in plasma represents its relative release rate from adipose tissue. Data from studies conducted in isolated adipocytes and in regional subcutaneous adipose tissue suggest that the relative rate of release of specific fatty acids from adipose tissue into plasma is influenced by fatty acid structure (7)(8)(9)(10)(11)(12)(13)(14). However, the relationship between whole-body systemic fatty acid kinetics and adipose tissue fatty acid composition is not known.…”

The Relation between Non-adipose Muscle Fat and Hepatic Steatosis Studied with Localized 1H Magnetic Resonance Spectroscopy (1H MRS) and LC-MS Techniques

“…E.g. if we consider for rodents only the adipose tissue there are in principle four adipose pools: retroperitoneal, epididymal, mesenteric and subcutaneous [17].…”

“…In mice, in principle, fat cells can be isolated from four adipose pools: retroperitoneal, epididymal, mesenteric and subcutaneous [17]. However, little information is available about the role of fat from non-adipose tissue stores like intramuscular fat in relation to organs like the liver.…”