Modulation by Docosahexaenoic Acid of the Epinephrine‐Stimulated Adenylate Cyclase Activity of the Bovine Retina

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Abstract
This work shows that unsaturated fatty acids enhance the epinephrine-stimulated adenylate cyclase activity in bovine retina. The modulating effect on the epinephrine-stimulated formation of cyclic AMP seems to be linked to the degree of unsaturation of the fatty acid. Treatment of the intact retina with docosahexaenoic acid in the concentration range 0.5 .times. 10-6 -1 .times. 10-3 M does not affect the enzyme activity measured in the absence of the hormone but markedly increases the cyclase activity when the tissue is incubated in the presence of 0.1 mM epinephrine. Docosahexaenoic acid enhances the maximal response to epinephrine without affecting the apparent ED50 value for this effector. Docosahexaenoic acid at 0.5 mM also increases the hormone-stimulated adenylate cyclase activity in retinal cell-free homogenate, whereas it has not effect on the epinephrine-sensitive enzyme solubilized from the membrane fraction with 1% Triton X-305. When docosahexaenoic acid-preincubated intact retina and cell-free homogenate are incubated inthe presence of defatted albumin, both the observed activating effect of the fatty acid on the epinephrine-stimulated adenylate cyclase activity and the enhancement of the enzyme response to the hormone significantly diminish.