RESUMEN
1. The effect of fish oil administration by gavage (0.4% body weight) on activities of superoxide dismutase (SOD), catalase and glutathione peroxidase (GSH-Px) and on content of thiobarbituric acid reactive substances (TBARs) of the lymphoid organs [thymus, spleen and mesenteric lymph nodes (MLN)] and liver was investigated in 21-day pregnant rats. The results were compared with those obtained by administration of soybean oil, cocoa butter and coconut oil. 2. Oil administration did not have any significant effect on antioxidant enzyme activities of the liver, whereas marked changes were found in the lymphoid organs. The MLN presented the most pronounced changes: SOD and catalase activities were increased by the four oils; GSH-Px activity was raised by soybean and fish oils; coconut oil reduced the activity of the three antioxidant enzymes in this organ. 3. Fish oil given by gavage does affect the antioxidant capacity of the lymphoid organs; however, similar effect was also observed for cocoa butter and soybean oil. These changes in the antioxidant enzyme activities were able to prevent the lipid peroxidation process in the lymphoid organs.