Short communication: Dietary conjugated linoleic acid down-regulates fatty acid transporters in the mammary glands of lactating rats.

Recent studies indicated that reduction of milk triacylglycerol concentrations by dietary conjugated linoleic acid (CLA) involves an impairment of both de novo fatty acid synthesis and uptake of fatty acids from circulating triacylglycerol-rich lipoproteins into the mammary gland. However, nonesterified fatty acids (NEFA) in the plasma released from adipose tissue and taken up into the mammary gland by fatty acid transporters are a further important source of fatty acids available for milk triacylglycerol synthesis. Therefore, the aim of the present study was to investigate the effect of dietary CLA on plasma concentrations of NEFA and the expression of fatty acid transporters in the mammary glands of lactating rats fed either a CLA diet or a control diet. Dams fed diets with CLA had a greater concentration of NEFA in plasma than those fed the control diet. In addition, relative mRNA concentrations of fatty acid transporters (fatty acid translocase/CD36, fatty acid transport protein, and plasma membrane fatty acid binding protein) were about 45, 75, and 70% lower, respectively, in the mammary gland of dams fed diets with CLA compared with those fed the control diet. In conclusion, the present findings indicate that reduced uptake of circulating NEFA released from white adipose tissue into the mammary gland could also contribute to the reduction of milk triacylglycerol concentrations by dietary CLA in rats. The mechanism through which CLA inhibits expression of fatty acid transporters deserves further study.