EFFECT OF INVIVO MODULATION OF MEMBRANE DOCOSAHEXAENOIC ACID LEVELS ON THE DOPAMINE-DEPENDENT ADENYLATE-CYCLASE ACTIVITY IN THE RAT RETINA

Abstract: We have studied the effect of a dietary deprivation of n‐3 fatty acids on the activity of the dopamine (DA)‐de‐pendent adenylate cyclase in the rat retina. Experiments were conducted in 6‐month‐old rats raised on semipurified diets containing either safflower oil (n‐3 deficient diet) or soybean oil (control diet). The levels of docosahexaenoic acid [22:6 (n‐3)] in retinal phospholipids were significantly decreased in n‐3 deficient rats (35–42% of control levels). This was compensated by a rise in 22:5 (n‐6), the total content of poly‐unsaturated fatty acids (PUFA) remaining approximately constant. Adenylate cyclase activity was measured in retinal membrane preparations from dark‐adapted or light‐exposed rats. The enzyme activity was stimulated by DA and SKF 38393 in a light‐dependent fashion. The activation was lower in rats exposed to light than in dark‐adapted animals, suggesting a down‐regulation of the DI DA receptors by light. The activation by guanine nucleotides and forskolin was also decreased in light‐exposed rats. There was no significant effect of the dietary regimen on the various adenylate cyclase activities and their response to light. Furthermore, the guanine nucleotide‐ and DA‐dependent adenylate cyclase activities of retinal membranes were found to be relatively resistant to changes in membrane fluidity induced in vitro by benzyl alcohol. The results indicate that in the absence of changes in total PUFA content, a decreased ratio of n‐3 to n‐6 fatty acids in membrane phospholipids does not significantly affect the properties of adenylate cyclase in the rat retina. Copyright © 1990, Wiley Blackwell. All rights reserved