In vivo metabolism of plasma free fatty acids by intestinal mucosa of man

Abstract

Intestinal metabolism of plasma free fatty acids was studied in 12 patients in vivo. After rapid intravenous injection of [14C]palmitic acid complexed to human albumin, serial jejunal biopsies were performed with a hydraulic biopsy tube. Specimens of jejunal mucosa were homogenized and assayed for lipids and radioactivity. The mean half-time of initial 14C-free fatty acid disappearance from plasma was 2.0 min. Uptake of 14C-plasma free fatty acids by the mucosa of the entire small bowel was estimated as 0.7%. Of mucosal radioactivity, 25.2% was recovered in water-soluble metabolites, suggesting local oxidation of plasma free fatty acids; 31.7% was incorporated into phospholipids, 16.5% into triglycerides, and 9.7% was esterified with cholesterol. The specific activity of mucosal triglyceride-fatty acids was about 10-fold higher than the specific activity of serum triglyceride-fatty acids during the first 15 min after the intravenous injection of [14C]palmitate, thereby establishing for the first time in man in situ esterification of plasma free fatty acids by intestinal mucosa. We therefore conclude that in man, plasma free fatty acids also serve as a constantly available source of energy and of precursors for more complex lipids in the absorptive intestinal epithelium. It is speculated that, as in rats, part of the ester lipid synthesized in situ from plasma free fatty acids may subsequently leave the absorptive epithelial cells incorporated in lipoproteins. Quantitatively this pathway must be minute, however, under normal conditions.