DIETARY DEFICIENCY OF N-3 FATTY-ACIDS ALTERS RHODOPSIN CONTENT AND FUNCTION IN THE RAT RETINA

Purpose. To investigate the possibility that previously demonstrated r eductions in photoreceptor sensitivity to light in n-3 fatty-acid-defi cient rats can be explained by alterations in rhodopsin content and/or function. Methods. Sprague-Dawley rats were reared throughout gestati on, lactation, and up to 24 weeks of age on a diet containing safflowe r oil (n-3 fatty-acid-deficient) or soybean oil as the sole source of lipids. Dark-adapted content and in vivo regeneration of rhodopsin aft er bleaching were measured by detergent extraction. The regeneration r ate constants and number of photons absorbed by rhodopsin under steady -state bleach conditions were calculated from these values. The rate o f metarhodopsin II (MII) formation in vitro was determined by flash bl eaching extracted pigment and native rod outer segment membranes. Rod outer segment length and photoreceptor cell density were determined in histologic sections through the inferior central retina. Results. Dar k-adapted rhodopsin content of retinas from rats reared on safflower o il was 12% to 15% higher than that of rats raised on soybean oil at ev ery age measured. The rate of rhodopsin regeneration was significantly slower in rats reared on safflower oil while the level of steady-stat e bleach was the same. This meant that the rats reared on safflower oi l absorbed about one half as many photons during light exposure. The r ate of metarhodopsin II formation in vitro was unaffected by n-3 fatty acid deficiency. No difference in either rod outer segment length or cell number was detected. Conclusion. A reduced capacity for photon ab sorption by rhodopsin could play a role in lowering retinal sensitivit y to light in n-3 fatty-acid-deficient rats.