Evidence of accumulation of ceramides containing [14C]nervonic acid in the rat lung following injection of [14C]erucic acid.

A mixture of albumin-bound [14C]erucate and [3H]oleate was injected into rats fed a stock pellet diet containing 4% by weight of lipid. Chylomicrons containing the same labelled fatty acids were also injected into rats fed diets containing 15% by weight of rapeseed oil (48% of erucic acid), canbra oil (less than 5% of erucic acid) or ground nut oil (no erucic acid). Lung lipids were analyzed at various times after injection. In all cases, except in the rapeseed oil diet group, 14C radioactivity of lung 'monoacylglycerol' was ten times higher than 3H radioactivity. More than 85% of this 14C radioactivity was found in nervonic acid (24 : 1). It was shown by TLC and GLC analysis that 85-90% of the 14C radioactivity of this fraction was in ceramides (N-acyl-4-sphingenine). Ceramides containing [14C]nervonic acid disappeared from the lung with time and their incorporation with time into sphingomyelin was also observed. The absence of accumulation of 3H and 14C (18 : 1) in ceramides showed that oleic acid was not incorporated into sphingomyelin in the same way as nervonic acid. In the rapeseed oil diet group, there was no accumulation of 14C radioactivity in ceramides and conversion of erucic acid into nervonic acid was less, and into oleic acid more, than in other diet groups indicating a possible enzyme adaptation.