1-C-14-Linoleic acid distribution in various tissue lipids of guinea pigs following an oral dose

A recent study on the metabolism of 1-C-14-alpha -linolenic acid in the gui nea pig revealed that the fur had the highest specific activity of all tiss ues examined, 48 h after dosing. The present study investigated the pattern of tissue lipid labeling following an oral dose of 1-C-14-linoleic acid af ter the animals had been dosed for the same time as above. Guinea pigs were fed one of two diets with a constant linoleic acid content (18% total fatt y acids) and a different content of alpha -linolenic acid (0.3 or 17.3%) fr om weaning for 3 wk and 1-C-14-linoleic acid was given orally to each anima l for 48 h prior to sacrifice. The most highly labeled tissues (dpm/mg of l inoleic acid) were liver, followed by brain, lung and spleen, heart, kidney and adrenal and intestines, in both diet groups. The liver had almost a th reefold higher specific activity than skin and fur which was more extensive ly labeled than the adipose and carcass. Approximately two-thirds of the la bel in skin plus Fur was found in the fur which, because of a low lipid mas s, would indicate that the fur was highly labeled. All tissues derived from animals on the diet With the low alpha -linolenic acid level were signific antly more labeled than the tissues from the animals on the high alpha -lin olenic acid diet, by a factor of 1.5 to 3. The phospholipid fraction was th e most highly labeled fraction in the liver, free fatty acids were the most labeled fraction in skin & fur, while triacyglycerols were the most labele d in the carcass and adipose tissue. In these tissues, more than 90% of the radioactivity was found in fatty acids with 2-double bonds in the tissue l ipids. These data indicate that the majority of label found in guinea pig t issues 48 h after dosing was still associated with a fatty acid fraction wi th 2-double bonds, which suggests there was little metabolism of linoleic a cid to more highly unsaturated fatty acids in this time frame. In this stud y, the labeling of guinea pig tissues with linoleic acid, 48 h after dosing , was quite different from the labeling with alpha -linolenic acid reported previously. The retention of the administered radioactivity from C-14-lino leic acid in the whole body lipids was 1.6 times higher in the group fed th e low or-linolenic acid diet (diet contained a total of 1.8 g PUFA/100 g di et) compared with the group fed the high a-linolenic acid diet (diet contai ned 3.6 g PUFA/100 g diet). The lack of retention of C-14-labeled lipids in the whole body would be consistent with an increased rate of beta -oxidati on of the labeled fatty acid on the diet rich in PUFA, a result supported b y other studies using direct measurement of labeled carbon dioxide.