Leptin resistance during pregnancy is also exerted at the periphery.

Pregnancy is a physiological state with a great demand of energy and nutrients in mammals and is characterized by hyperphagia, increase in fat mass, hyperleptinemia, and central resistance to leptin. In order to evaluate whether pregnancy is also a state of leptin resistance at the periphery, we studied the response to leptin in the liver and subcutaneous adipose tissue (SAT). We demonstrated reduced levels of phosphoryalated signal transducer and activator of transcription 3 (p-STAT3) and phosphorylated protein kinase B (p-AKT) after intravenous leptin in both tissues in mid-term pregnant rats (G13) and a restored response in late pregnancy (G18). As underlying mechanisms of the peripheral leptin resistance of mid-gestation we found decreased leptin receptor b (LepRb) mRNA levels and increased content of suppressor of cytokine signaling 3 (SOCS3). Furthermore, we demonstrated that in G13 rats the main lipogenic molecules and activity (sterol regulatory element binding transcription protein 1 (SREBP-1) and fatty acid synthase (FAS)) were elevated in the liver and SAT, and the molecules involved in β-oxidation (peroxisome proliferator activated receptor α (PPARα) and carnitine palmitoyltransferase 1 (CPT-1)) were reduced, as it happens in early pregnancy. In G18, the opposite pattern is observed. This probably reflects that in G13 the peripheral resistance to the hyperleptinemia might help maintaining the lipogenic metabolism of early pregnancy. In contrast, the recovery of the response to leptin in late pregnancy would favor a catabolic metabolism. Finally, using a pseudogestation model we showed that progesterone and prolactin are not involved in the gestational peripheral leptin resistance. In conclusion, during mid-pregnancy a state of leptin resistance is also exerted at the periphery, and is probably involved in the characteristic lipid regulation of this physiological state.