EFFECT OF REPRODUCTIVE STATES ON LIPID MOBILIZATION AND LINOLEIC-ACIDMETABOLISM IN MAMMARY-GLANDS

Effects of pregnancy and lactation on lipid metabolism in mouse mammar y fat pads and nonmammary adipose tissues have been studied. In order to address the question whether the influence of hormonal milieu on li pid metabolism in mammary epithelial cells during pregnancy and lactat ion is the same as in fat cells, we have studied the mobilization of l ipids and metabolism of fatty acids in the intact mammary glands, pare nchyma-free mammary fat pads and in the perimetrial rat tissues of vir gin, pregnant and lactating mire. Compared to parenchyma-free mammary fat pads, the perimetrial adipose tissues accumulated 5-fold higher le vels of triglycerides during pregnancy. Mammary fat cells maintained o verall lipid levels during pregnancy and lactation (16-20 mu g/fat pad ). In contrast, lactation depleted total lipid stores from 108 +/- 5 t o 24 +/- 4.5 mu g/fat pad in perimetrial fat pads. Results of comparat ive analysis of fatty acid composition of mammary fat pads, with and w ithout epithelial tissue, from virgin and lactating mice showed stimul ation of 18:2 omega 6 metabolism leading to 130% increase in the ratio 20:4 omega 6 to 18:2 omega 6 in the epithelial compartment. Pregnancy and lactation resulted in the elevation of 20:406 levels probably due to a 4-fold increase in Delta 5 desaturase activity and a decrease in oxidative degradation of 18:2 omega 6. These results suggest that, un like other adipose tissues, the metabolic pathways in mammary fat cell s are not dedicated to sequestration and accumulation of dietary lipid s during pregnancy. Lactation favors mammary epithelial cell-stimulate d production of precursors of eicosanoids which are known to have agon ist-like effect on mammary epithelial cells.