Conservation of Docosahexaenoic Acid in the Retina

Docosahexaenoic acid (22:6n-3), a polyunsaturated fatty acids (PUFA) of the n-3 family, makes up about half of the total fatty acids of vertebrate rod outer segment (ROS) phospholipids (see review by Fliesler and Anderson, 1983). This level of 22:6n-3 is among the highest reported for any membrane. The reason for the large amount of 22:6n-3 in ROS is not known, although it has been observed that membranes that are active metabolically, as in ROS, mitochondria, sperm, and synaptic vesicles, have high levels of PUFAs, while relatively inactive membranes such as myelin have low PUFA levels (Dratz and Deese, 1986; see books edited by Simopoulos et al., 1986 and Lands, 1987). Over the past 15-20 years, evidence has accumulated suggesting that 22:6n-3 is important in maintaining the normal structure and function of the retina.