Lysosomal Enzyme Activities Are Decreased in the Retina and Their Circadian Rhythms Are Different from Those in the Pineal Gland of Rats Fed an α-Linolenic Acid–Restricted Diet

The retinal rod outer segment (ROS) is shed and digested daily by phagosomes in retinal pigment epithelial (RPE) cells. We previously observed significantly fewer large phagosomes in rats fed an α-linolenic acid (ALNA)-deficient diet. Rats fed a safflower oil diet (ALNA-restricted) or a perilla oil diet (ALNA-sufficient) through two generations were adapted to a 24-h cycle with light from 0700 to 1900 h. They were killed at 0500, 0900, 1300 and 1700 h to determine the activities of four lysosomal enzymes in retina, including β-glucosidase, β-glucuronidase, hexosaminidase and acid phosphatase. The enzyme activities at 0500 h were the lowest and then increased gradually until 1700 h, exhibiting similar circadian rhythms in the two dietary groups. However, the activities at each time point were significantly lower in the safflower group. In the pineal gland, the activities were maximum at 1300 h, except for β-glucosidase, and were not different between groups. These diets had qualitatively similar but quantitatively different effects on the fatty acid compositions of the retina and the pineal gland. These results indicate that decreased amplitudes in electroretinogram and altered size distribution of phagosomes, as induced by a restricted intake of ALNA, are associated with decreased lysosomal enzyme activities in the retina but not in the pineal gland.