Daily variations of the biosynthesis and composition of fatty acids in rats fed on complete and fat-free diets.

This report describes the daily changes in fatty acid composition and fatty acid desaturation in rats feeding on a complete diet and a fat-free diet successively. Rats on a complete diet showed a good homeostasis in the percentage of fatty acid in plasma, with a possible palmitic acid rhythm, but the fat-free diet initiated an essential fatty acid-deficient pattern in a few hours. The light-dark period in animals feeding on a complete diet motivates a feeding rhythm that causes changes in linoleic and arachidonic acids in the whole liver and microsomes that are related to delta 6 and delta 5 desaturase activities. The patterns of delta 6 and delta 5 desaturase changes were different. Linoleic acid intake during the dark periods (complete diet feeding) caused a decrease of delta 6 desaturase activity and the activation of delta 5 desaturation that led to an increase of arachidonic acid biosynthesis. The feeding of a fat-free diet eliminated the rhythm observed in linoleic and arachidonic acid composition in the liver and changed the desaturase rhythms. The delta 9 desaturase activity in the liver also showed a daily rhythm in the complete-diet period that disappeared with the change to a fat-free diet, while the activity increased markedly. A negative correlation existed between the percentage of linoleic acid in the liver and the delta 9 desaturase activity. However, no correlation was found between delta 9 desaturase activity and the percentage of 16:1 and 18:1 in the complete-diet period.