EFFECT OF MATERNAL DIETARY FATS WITH VARIABLE N-3/N-6 RATIOS ON TISSUE FATTY-ACID COMPOSITION IN SUCKLING MICE

This report examines the distribution of n-3 and n-6 fatty acids in heart, kidney and liver phosphatidylcholine and phosphatidylethanolamine of suckling mice from dams fed a fat-supplemented diet with variable n-3/n-6 ratios. After conception and throughout the pregnancy and lactation period, dams were fed a fat-free liquid diet supplemented with 20% by energy of oil mixtures (fish oil concentrate, rich in 20:5n-3 and 22:6n-3, and safflower oil concentrate, rich in 18:2n-6). The diets contained similar amounts of combined n-3 and n-6 fatty acids but variable ratios of n-3 to n-6 fatty acids (0, 0.25, 0.5, 1, 2 and 4). In 12-day-old suckling mice, as the n-3/n-6 ratio in the maternal diet increased (up to approx. 0.5), the tissue levels of 20:5n-3, 22:5n-3 and 22:6n-3 increased, whereas those of 18:2n-6 and 20:4n-6 decreased. The responses were similar in both phospholipid subclasses, but varied between different tissues. Generally, the n-3/n-6 ratios were significantly greater in pup tissues than in milk fat, indicating preferential incorporation of n-3 over n-6 fatty acids into phospholipids during growth. However, the incorporation of n-3 fatty acids in pups was significantly suppressed whereas that of n-6 fatty acids was increased when 18:2n-6 was replaced by its DELTA-6-desaturation product, 18:3n-6 (concentrated from evening primrose oil), as the source of n-6 fatty acid. This result suggests that DELTA-6 desaturase activity in neonate tissues is low, and consequently, the metabolism of 18:2n-6 to longer chain n-6 fatty acids is reduced. The preformed long-chain n-3 fatty acids, which bypass DELTA-6-desaturation, were thus, preferentially incorporated into tissue phospholipids.