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 (0,025, 0.5, 1, 2, and 4). In 12‐day‐old suckling mice, as the n−3nn−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 δ6‐desaturation product, 18∶3n−6 (concentrated from evening primrose oil), as the source on n−6 fatty acid. This result suggests that δ6 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 δ6‐desaturation, were thus, preferentially incorporated into tissue phospholipids.