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Deficiency of (n-6) but Not (n-3) Polyunsaturated Fatty Acids Inhibits the Secretagogue Effect of Prolactin in Lactating Rat Mammary Epithelial Cells¹

^* Laboratoire de Biologie Cellulaire et Moléculaire et Laboratoire de Nutrition et Sécurité Alimentaire, Institut National de la Recherche Agronomique, 78352 Jouy-en-Josas Cedex, France

The repercussions of various kinds of dietary polyunsaturated fatty acid (PUFA) deficiencies on the fatty acid composition of membranes and on the secretory activity of lactating female rat mammary epithelial cells were investigated. Primiparous female rats were fed different PUFA diets from weaning: adequate (n-6) and (n-3) PUFA supply; overall PUFA deficiency; specific (n-6) PUFA deficiency or specific (n-3) PUFA deficiency. Mammary gland phospholipids contained very low amount of (n-3) PUFA in control rats, and only 1% docosahexaenoic acid. The fatty acid composition of membrane phospholipids reflected the type of diet received by the animals, i.e., the diets deficient in the (n-3) or (n-6) PUFA series resulted in lower (n-3) or (n-6) PUFA, and the (n-3) + (n-6) deficient diet caused a true overall PUFA deficiency in the membranes. The morphology of cells from overall PUFA- or (n-6) PUFA-deficient rats showed an accumulation of secretory vesicles in the cytoplasm. Basal casein secretion was independent of the diet and of the composition of membrane phospholipids. However, prolactin did not have a secretagogue effect on cells from (n-6) PUFA- or overall PUFA-deficient rats but retained this effect on cells from (n-3)-deficient rats. These results emphasize the specific role of (n-6) PUFA in the functioning of the lactating mammary epithelial cell.

KEY WORDS: • rats • polyunsaturated fatty acids • mammary epithelial cells • prolactin • secretion

¹ The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

² To whom correspondence should be addressed.

Manuscript received 9 December 1992. Initial review completed 9 February 1993. Revision accepted 26 July 1993.