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Abstract
PURPOSE: To investigate the possibility that previously demonstrated reductions in photoreceptor sensitivity to light in n-3 fatty-acid-deficient rats can be explained by alterations in rhodopsin content and/or function. METHODS: Sprague-Dawley rats were reared throughout gestation, lactation, and up to 24 weeks of age on a diet containing safflower oil (n-3 fatty-acid-deficient) or soybean oil as the sole source of lipids. Dark-adapted content and in vivo regeneration of rhodopsin after bleaching were measured by detergent extraction. The regeneration rate constants and number of photons absorbed by rhodopsin under steady-state bleach conditions were calculated from these values. The rate of metarhodopsin II (MII) formation in vitro was determined by flash bleaching 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: Dark-adapted rhodopsin content of retinas from rats reared on safflower oil was 12% to 15% higher than that of rats raised on soybean oil at every age measured. The rate of rhodopsin regeneration was significantly slower in rats reared on safflower oil while the level of steady-state bleach was the same. This meant that the rats reared on safflower oil absorbed about one half as many photons during light exposure. The rate 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 absorption by rhodopsin could play a role in lowering retinal sensitivity to light in n-3 fatty-acid-deficient rats.