EFFECT OF DIETARY-FAT AND ENVIRONMENTAL LIGHTING ON THE PHOSPHOLIPID MOLECULAR-SPECIES OF RAT PHOTORECEPTOR-MEMBRANES

We have previously shown that retinas of albino rats adapt to bright cyclic light (500-800 Ix) by lowering the levels of docosahexaenoic acid (22:6n-3) in their rod outer segment (ROS) phospholipids. In the present study, we addressed the role of dietary fat in this process. Pregnant rats were kept in I Ix or 250 Ix cyclic illuminance (12L:12D) and fed diets containing 10% (by weight) of either hydrogenated coconut oil (COG, no n-3 or n-6 fatty acids), linseed oil (LIN, n-3 and n-6 fatty acids), or safflower oil (SAF, only n-6 fatty acids), starting 4 days before delivery. Pups were weaned at 3 weeks of age and continued on the same diet and light regime. At 12 weeks of age, 3 or 4 animals in each diet-light group were killed and the remaining animals were stressed continuously with 2000 Ix light for 24 hr and then kept in 1 Ix cyclic light for 10 days. Fatty acids and phospholipid molecular species (PLMS) of ROS membranes were determined. For prestressed groups, those animals fed the LIN diet had high levels of 22:6n-3 and PLMS containing 22:6n-3, with little 22:5n-6. Compared to the LIN group, the COC and SAF groups had lower levels of 22:6n-3- and 22:6n-3)-containing PLMS and higher levels of 22:5n-6 and molecular species containing 22:5n-6, such as 22:5n-6/22:6n-3, 16:0/22:5n-6 and 18:0/22:5n-6. Within each dietary group, animals raised in 250 Ix cyclic illuminance had lower levels of 22:6n-3 and 22:5n-6 compared to those raised at 1 Ix, This light effect was greater for 22:6n-3 in the LIN group than for 22:5n-6 in the SAF group. After the acute light stress, those animals raised in I Ix showed dramatic reduction in PLMS containing 22:6 n-3 and 22:5n-6, especially polyenoic species such as 22:6n-3/22:6n-3 in the LIN group and 22:5n-6/22:6n-3 in the COC and SAF groups. In contrast, animals raised in 250 Ix showed much smaller changes. These results demonstrate that: (1) the fatty acid and PLUMs compositions of rat ROS can be dramatically altered when pregnant animals are fed diets devoid of n-3 and/or n-6 essential fatty acids; (2) the level of 22:5n-6 and 22:6n-3 in ROS phospholipids is significantly affected by the level of cyclic rearing illuminance and (3) acute light stress has a dramatic effect on ROS PUFA in dim cyclic reared rats compared to those raised in bright cyclic light.