Diurnal rhythms of retinal phospholipid synthetic enzymes are retained buttheir activities are decreased in rats under alpha-linolenic acid deficiency

Rats fed a safflower oil (a-linolenic acid (ALNA)-deficient) diet over the course of two generations had significantly decreased docosahexaenoic acid (22:6n-3) and increased docosapentaenoic acid (22:5n-6) contents in the maj or retinal phospholipids such as phosphatidylcholine (PC), phosphatidyletha nolamine (PE), and phosphatidylserine (PS) when compared with those fed a p erilla oil (ALNA-sufficient) diet, but the compositions of phosphatidylinos itol acyl chains were relatively unaffected. The contents of individual pho spholipids in the retina were essentially the same for the two dietary grou ps. The activities of the rate-limiting enzymes in the de novo synthesis of PC and PE, CTP:phosphocholine cytidylyltransferase (CT), and CTP:phosphoet hanolamine cytidylyltransferase (ET), respectively, were measured in the re tinas excised at 5:00, 9:00, 13:00, and 17:00 h from rats adapted to a 24-h cycle with lights on from 7:00 to 19:00 h. Both enzymes exhibited signific ant diurnal rhythms with the lowest activities at 5:00 h and gradually incr easing activities following exposure of the rats to light; the maximum acti vities were at 13:00 h for CT and 17:00 h for ET. The diurnal rhythms were not significantly affected by the above-mentioned diets. However, both enzy me activities at each collection time point were significantly lower in the safflower oil group than in the perilla oil group. These results suggest t hat retinal phospholipid turnover associated with shedding, phagocytosis, a nd resynthesis of the rod outer segments is limited by ALNA deficiency. (C) 2000 Academic Press.