Incorporation of 14C into tissue lipids after oral administration of [1-14C]linoleic acid in rats fed different levels of essential fatty acids.

Rats from an inbred Sprague-Dawley strain were fed purified diets with a low (0.3% of the total energy), normal (3%) or high (10%) content of essential fatty acids (EFA) for several generations. Thirty- to 34-d-old male rats of at least the sixth generation to be fed these diets were given a single intragastric dose of [1-14C]linoleic acid in olive oil, and the respiratory CO2, urine and feces were collected for 20 h. The 14C activity was determined in the respiratory CO2, urine and feces as well as in total lipids and lipid classes of the whole animal and in nine tissue groups. The content of total lipids and lipid classes was similar in all groups. The rats in the low EFA group retained significantly more radioactivity (51%) in the tissues than the rats fed the normal EFA (34%) or the high EFA (27%) diets. In all groups most of the radioactivity was found in the skeletal muscles, skin, liver and white fat, but the retention was greater in the low EFA group than in the other groups, except in the white and brown fat. In the carcass and most tissues, the proportion of the retained 14C activity recovered in the phospholipids increased with decreasing EFA level in the diet, whereas in the triglycerides the opposite was found. Expressed as percent of administered dose, the total retention of radioactivity in the phospholipids was 31, 13 and 8% in the low, normal and high EFA group, respectively, while the retention in the triglycerides was about the same in all groups (17-18%).