Dietary 204n-6 and 226n-3 Modulates the Profile of Long- and Very-Long-Chain Fatty Acids, Rhodopsin Content, and Kinetics in Developing Photoreceptor Cells

The objective of this study was to determine whether addition of dietary 204n-6 and 226n-3 to a conventional infant formula fat blend influences membrane long-chain and very-long-chain fatty acid composition, rhodopsin content, and rhodopsin kinetics in developing rat photoreceptor cells. The dietary fats were formulated based on the fat composition of a conventional infant formula providing an 182n-6/183n-3 ratio of 71 (SMA, Wyeth Nutritionals), which served as the control fat blend. This dietary fat blend was modified to contain 204n-6 arachidonic acid (AA), 226n-3 docosahexaenoic acid (DHA), AA DHA, or an 182n-6/183n-3 ratio of 41 (-linolenic acid). Dams were fed diets from birth, and rat pups were fed the same diet after weaning. Retinas and rod outer segments were prepared in the dark from pups at 2, 3, and 6 wk of age for fatty acid analysis of individual phospholipids, rhodopsin content, and rhodopsin disappearance kinetics after light exposure. Feeding AA DHA in the diet increased 226n-3 levels in phosphatidylcholine and phosphatidylethanolamine. In phosphatidylcholine, total n-6 tetraenoic very-long-chain fatty acids and total n-3 pentaenoic and n-3 hexaenoic very-long-chain fatty acids increased after feeding AA and DHA, respectively. Developmental changes were characterized by a decrease in 204n-6 in the major phospholipids, whereas 226n-3 increased with age in rod outer segments. The highest rhodopsin content occurred in the retina of rats fed diets containing AA and/or DHA. The kinetics of rhodopsin disappearance after light exposure was highest in rats fed DHA at 6 wk of age. This study demonstrates that small manipulations of the dietary level of 204n-6 and 226n-3 are important determinants of fatty acid composition of membrane lipid and visual pigment content and kinetics in the developing photoreceptor cell.