Abstract
The fatty acid composition of microsomal lipids and the activities of Delta 9- and Delta 6-desaturases in liver microsomes of rats fed diets supplemented with beta -carotene and two levels of 13-cis-retinoic acid were studied. Four groups of male, weanling rats were fed semipurified diets containing 0 or 100 mg beta -carotene per kg diet, and 20 or 100 mg 13-cis-retinoic acid per kg diet. After 11 weeks of feeding, the rats were killed, liver microsomes were prepared and assayed for Delta 9-desaturase and Delta 6-desaturase activities. The activity of Delta 9-desaturase was lower in liver microsomes of rats fed beta -carotene-supplemented diet or the diet supplemented with the higher level of 13-cis-retinoic acid. Microsomal Delta 6-desaturase activity was, however, higher in liver of rats fed 13-cis-retinoic acid; there was no effect of beta -carotene on Delta 6-desaturase activity. The fatty acid compositional data on total lipids of liver microsomes were consistent with the diet-induced changes in fatty acid desaturases. Phospholipid composition of liver microsomes was also altered as a result of feeding beta -carotene or 13-cis-retinoic acid-containing diets. The proportions of phosphatidyl-ethanolamine were generally higher, whereas those of phosphatidylcholine were lower in the experimental groups as compared with the control.