Effect of dietary DHA on DHA levels in retinal rod outer segments in young versus mature rats.

We compared the effect of direct supplementation with docosahexaenoic acid (DHA) on the fatty acid composition of the liver and the rod outer segment (ROS) membranes of the retina in young (five-week-old) and mature (one-year-old) rats. In young rats, a high content of DHA in the diet (9.7% of total energy) effectively increased the proportion of DHA in ROS membranes (41.8%), compared with the proportion observed in a linoleic acid (LA) diet group (control, 31.6%). The proportion of DHA was also significantly higher in the livers of young DHA-fed rats. These results show that direct supplementation with DHA is very effective in increasing DHA levels in the ROS membranes and livers of developing animals. In contrast, in mature rats there was no significant increase in the proportion of DHA in the ROS membranes, even after the highest dose (8.4% of total energy) of DHA, although the proportion of DHA was significantly higher in the livers of DHA-fed rats. The changes in fatty acid composition in the ROS membranes were different in young and mature rats fed high-DHA diets. Our findings indicate that mature rats maintain a constant level of DHA in the ROS membranes even after being directly supplemented with high doses of DHA.