Fasting-induced adipose factor identified as a key adipokine that is up-regulated in white adipose tissue during pregnancy and lactation in the rat

Adipokines, which are expressed and secreted from white adipose tissue (WAT), are potential factors that could contribute to the changes in energy homeostasis that occurs in pregnancy and lactation to meet the nutrient demands of fetal growth and milk production. The aim was to identify adipokines that could be involved by measuring the pattern of their mRNA expression in adipose tissue. Adipokine mRNAs were measured by quantitative RT-PCR in RNA isolated from white and brown adipose tissue (BAT) of rats at days 7, 14 and 21 of pregnancy, day 7 of lactation and virgin at dioestrus phase. The results for leptin, adiponectin and resistin expression in WAT essentially confirmed previous studies and it is unlikely that they are directly involved in the metabolic adaptations. The relative amounts of the mRNAs of the adipokines in BAT were comparable with those in WAT, but the patterns of expression did not follow those in WAT, except for apelin. Visfatin mRNA in WAT was elevated 2.5-fold only at day 21 of pregnancy. Apelin mRNA in WAT was increased 2.2-fold at day 7 of pregnancy. Retinol-binding protein 4 mRNA in WAT decreased to 46% of control at day 14 of pregnancy. Fasting-induced adipose factor (FIAF) mRNA in WAT was 2.2- to 2.5-fold higher throughout pregnancy and lactation. The marked induction of FIAF identifies this adipokine as a potential regulator of the metabolic adaptations that occur during pregnancy and lactation.