Selective incorporation of docosahexaenoic acid in rat brain.

The incorporation of [14C]docosahexaenoic acid (22:6) into various lipid classes was compared with that of [3H]arachidonic acid (20:4) in developing rat brains in order to characterize the retention of 22:6. The percentage distribution of 20:4 in neutral glycerides was similar to the mass distribution and, of the phospholipids, 20:4 was incorporated into choline glycerophospholipids and inositol glycerophospholipids in relatively higher amounts. The incorporation of labeled 22:6 differed from that of 20:4, as it was incorporated into ethanolamine glycerophospholipids and triacylglycerols in greater amounts in comparison with its mass distribution. Further division of ethanolamine glycerophospholipids into diacyl, alkylacyl and alkenylacyl types revealed that the high incorporation of radioactive 22:6 in ethanolamine glycerophospholipids was predominantly due to its rapid incorporation into diacyl and alkylacyl compounds. The distributions of both radioactively labeled 20:4 and 22:6 among the three types of ethanolamine glycerophospholipids were compared with those of radioactively labeled glycerol. The value of [3H]20:4/[3H]glycerol was much higher in alkenylacyl-GPE than in alkylacyl-GPE, and this indicates that 20:4 is incorporated into alkenylacyl-GPE by a deacylation-reacylation mechanism. In addition, [14C]22:6 was incorporated into ether-linked ethanolamine phospholipids in a similar manner to 20:4. This observation suggests that 22:6 may be incorporated into alkenylacyl-GPE by the same rearranging system, while another possibility is that preferential synthesis of hexaene species may occur in the desaturation of alkylacyl-GPE.