Interconversion of alpha-linolenic acid in rat intestinal mucosa: studies in vivo and in isolated villus and crypt cells.

The desaturation-elongation of [14C]linolenic acid (n-3) in the rat small intestine was examined in homogenates of villus and crypt cells in vitro and in mesenteric lymph duct cannulated rats in vivo, using high performance liquid chromatography of fatty acid methyl esters with continuous flow measurement of 14C. Desaturation-elongation of [14C]18:3 to [14C]18:4, [14C]20:4, and [14C]20:5 (n-3) could be demonstrated in both villus and crypt cell homogenates, the rate of interconversion generally being highest in the villus cell fraction. For example, during incubation with 20 nmol [14C]linolenic acid (n-3), the average rates of delta 6 desaturation were 1.35 pmol/min per mg protein in villus and 0.93 pmol/min per mg protein in crypt cell homogenates. The acylation of [14C]linolenic acid (n-3) into phospholipids in crypt cells was twofold higher than in villus cells. Addition of 1-palmitoyl-sn-glycero-3-phosphocholine (20-240 microM) increased the incorporation of [14C]linolenic acid (n-3) into phosphatidylcholine, and decreased the interconversion of [14C]linolenic acid (n-3) to delta 6 and delta 5 desaturation products in both villus and crypt cells. 1-Palmitoyl-sn-glycero-3-phosphocholine also decreased the incorporation of 14C into triacylglycerols and phosphatidic acid, the decrease being more pronounced in the crypt cells.(ABSTRACT TRUNCATED AT 250 WORDS)