Circadian rhythm of eicosanoid formation as affected by dietary linoleate.

Circadian rhythms of eicosanoid formation were investigated in linoleic acid (LA) rich (sunflower seed oil, 13.3 cal% LA) and LA deficient (hydrogenated palm kernel fat, 0.5 cal% LA) diet fed male Wistar rats adapted to an artificial lighting regimen of 12 hours light and 12 hours darkness. Over a period of 24 hours we examined at 4 hour intervals eicosanoid formation in the aorta (PGI2, PGE, PGF2 alpha), in the heart (6-keto-PGF1 alpha, PGE, PGF2 alpha, TXB2), in the kidney (PGE, PGF2 alpha) and in the brain (PGE, PGF2 alpha). Two types of circadian variation curves were observed: Low eicosanoid formation in the light period and increase in the dark cycle (PGE in aorta and heart, TXB2 in heart). The increase in eicosanoid formation in the dark cycle was diminished after an LA deficient diet. Continuous decrease (PGI2 in aorta) and increase (PGE in the brain), respectively, in the course of the day, without differences between the two dietary groups. We assume that the circadian oscillations of eicosanoid formation might be of importance for the development of the circadian time structure of the organism.