The effects of dietary protein on the fatty acid composition and delta 6 desaturase activity of rat hepatic microsomes.

Recently, significant differences between rats fed a casein diet and rats fed a soybean protein diet have been observed in hepatic phospholipid fatty acid patterns (Sjöblom, L., and Eklund, A., Biochim. Biophys. Acta 1004, 187-192, 1990). The influence of these two diets on the delta 6 desaturase activity was investigated in the present study because the hepatic desaturase system is a source of unsaturated fatty acids. The rats fed a casein diet showed higher desaturase activity than those fed soybean protein when using either linoleic acid (P less than 0.005) or oleic acid (P less than 0.05) as substrates. The phosphatidylcholine fraction of hepatic microsomes showed increases in oleic acid (P less than 0.005) and 20:3 omega 9 (P less than 0.001) levels as well as decreases in stearic acid (P less than 0.001), linoleic acid (P less than 0.005) and arachidonic acid (P less than 0.005) levels in rats which were fed casein rather than soybean protein. Similar differences between the two groups were also observed in the phosphatidylethanolamine and phosphatidylinositol fractions. These data indicate that the qualitative properties of the dietary protein source may influence the fatty acid pattern of rat hepatic microsomes by interfering with delta 6 desaturase activity.