Release of individual fatty acids from human adipose tissue in vivo after an overnight fast

K J Halliwell,B A Fielding,J S Samra,S M Humphreys,K N Frayn

doi:10.1016/s0022-2275(20)37549-0

Abstract

The objective of this study was to investigate the mobilization of individual fatty acids from human subcutaneous adipose tissue in vivo. Concentrations of individual non-esterified fatty acids were measured in arterialized plasma and in the venous drainage from subcutaneous abdominal adipose tissue in eight normal subjects, after an overnight fast, and for the subsequent 6 h. Whilst the veno-arterial concentration difference for non-esterified fatty acids increased over this period, the relative proportions of different fatty acids remained constant. There was a close relationship between veno-arterial difference and arterialized concentration for the different fatty acids. The arterialized concentration of stearic acid consistently lay above the regression line drawn for unsaturated fatty acids (P = 0.001), probably reflecting lower clearance of stearic acid. The release of individual fatty acids was compared with their prevalence in adipose tissue triacylglycerol in biopsies taken from six subjects. Relative release decreased with increasing chain length, and for a given chain length increased with increasing unsaturation, in agreement with animal studies (P < 0.001 for differences in relative mobilization according to these two factors). The results suggest that the systemic plasma concentration of individual non-esterified fatty acids is determined by their release from adipose tissue, but that the relationship between release and systemic concentration for stearic acid is different from that for other fatty acids. The results confirm, in humans, differences in relative mobilization found previously in animal studies.

Highlights

The objective of this study was to investigate the mobilization of individual fatty acids from human subcutaneous adipose tissue in vivo
In the postprandial period non-esterified fatty acids (NEFA) release from adipose tissue reflects the action of lipoprotein lipase (LPL) as well as that of the intracellular hormone-sensitive lipase (HSL) [8]
A catheter (SecalonHydrocath 22-gauge, 10 cm; Ohmeda, Swindon, UK) was introduced into a superficial vein draining the subcutaneous abdominal adipose tissue and threaded anterogradely over a guide wire until its tip lay near to the inguinal ligament, as described previously [11].We have shown that blood drawn from such a catheter represents almost pure drainage from adipose tissue with at most a minor contribution from the overlying skin and no detectable contribution from muscle [12].The catheter was filled with saline, taped to the skin, and the subject slept in the hospital overnight

Summary

Introduction

The objective of this study was to investigate the mobilization of individual fatty acids from human subcutaneous adipose tissue in vivo. Studies in rats and rabbits have suggested that the mobilization of non-esterified fatty acids (NEFA) from adipose tissue may be selective,with preferential release of shorter-chain rather than longer-chain, and of polyunsaturated rather than saturated, fatty acids [1,2,3,4]. In these studies the animals have usually been fed on special diets in order to enrich the adipose depots with particular fatty acids [1,2,3,4]. By taking sequential samples over a 6-h period we have increased the precision of measurement of these concentrations

Objectives

Methods

Results