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Alteration of the Lipid Composition of Rat Testicular Plasma Membranes by Dietary (n-3) Fatty Acids Changes the Responsiveness of Leydig Cells and Testosterone Synthesis¹

Nutrition and Metabolism Research Group, Department of Foods & Nutrition ^* Department of Medicine, University of Alberta, Edmonton, Alberta, Canada T6G 2C2

Experiments were conducted to assess whether changing dietary fat composition altered phospholipid composition of rat testicular plasma membranes in a manner that altered receptor-mediated action of luteinizing hormone (LH)/human chorionic gonadotropin (hCG). Weanling rats were fed diets that provided high or low cholesterol intakes and that were enriched with linseed oil, fish oil or beef tallow for 4 wk. Feeding diets high in (n-3) fatty acids decreased plasma and testicular plasma membrane 20:4(n-6) content. A marked reduction of the 22:5(n-6) content and an increase in the 22:6(n-3) content of testicular plasma membrane was found only in animals fed fish oil. A decrease in binding capacity of the gonadotropin (LH/hCG) receptor in the plasma membrane, with no change in receptor affinity, was observed for animals fed either linseed oil or fish oil diets. Dietary treatments that raised plasma membrane cholesterol content and the cholesterol to phospholipid ratio in the membrane were associated with increased binding capacity of the gonadotropin receptor. Feeding diets high in 18:3(n-3) vs. those high in fish oil altered receptor-mediated adenylate cyclase activity in a manner that depended on the level of dietary cholesterol. Feeding diets high in cholesterol or fish oil increased basal and LH-stimulated testosterone synthesis relative to that in animals fed the low cholesterol diet containing linseed oil. It is concluded that changing the fat composition of the diet alters the phospholipid composition of rat testicular plasma membranes and that this change in composition influences membrane-mediated unmasking of gonadotropin receptor-mediated action in testicular tissue.

KEY WORDS: • dietary fat • luteinizing hormone/human chorionic gonadotropin receptor • testosterone synthesis • rat • adenylate cyclase

¹ Supported by the Natural Sciences and Engineering Research Council of Canada.

² Present address: Institute of Experimental Endocrinology, CFS, Slovak Academy of Sciences, Vlarska 3, Bratislava, Czechoslovakia.

³ M. L. Garg is an Alberta Heritage Foundation for Medical Research Postdoctoral Fellow.

⁴ M. T. Clandinin is a Scholar of the Alberta Heritage Foundation for Medical Research. Reprint requests should be addressed to Dr. M. T. Clandinin, Department of Foods and Nutrition, 318f Home Economics Building, University of Alberta, Edmonton, Alberta, Canada T6G 2M8.

Manuscript received 13 July 1987. Revision accepted 27 November 1989.