Long-term intake of trans (n-3) polyunsaturated fatty acids reduces the b-wave amplitude of electroretinograms in rats.

Weanling rats were fed three diets differing in their concentrations of the cis- and trans-isomers of a-linolenic acid [18:3(n-3)] for 12 mo to study the long-term effects of these fatty acids on the electroretinogram (ERG). The diets contained 18:3(n-3) in its natural form at 2.0 g/100 g total fatty acids (C group), partially isomerized 18:3(n-3) [1.3 g/100 g cis 18:3(n-3) + 0.7 g/100 g trans 18:3(n-3); cT group] and the control level of cis 18:3(n-3) with trans 18:3(n-3) [2.0 g/100 g cis 18:3(n-3) + 0.7 g/100 g trans 18:3(n-3); CT group]. The ERG and the levels of trans-isomers of the polyunsaturated fatty acids (PUFA) of retinal and hepatic phospholipids were determined after 3, 6, 9 and 12 mo of feeding the experimental diets. Dietary trans alpha-linolenic acid altered the fatty acid composition of retinal and hepatic phospholipids by significantly increasing the Delta19trans-isomer of docosahexaenoic acid. Moreover, dietary trans-isomers of alpha-linolenic acid significantly decreased the b-wave amplitude of the ERG by 9 mo of feeding. We conclude that long-term intake of small amounts of trans-isomers of alpha-linolenic acid could disturb visual function. However, further studies are required to determine the mechanisms responsible for this phenomenon.