Long-term hypoxia increases leptin receptors and plasma leptin concentrations in the late-gestation ovine fetus

This study was designed to test the hypothesis that long-term hypoxia (LTH) increases fetal plasma leptin and fetal adipose or placental leptin expression and alters hypothalamic and adrenocortical leptin receptor (OB-R) expression. Pregnant ewes were maintained at high altitude (3,820 m) from day 30 to ∼130 days of gestation. Reduced PO₂ was maintained in the laboratory by nitrogen infusion through a maternal tracheal catheter. On day 132, normoxic control and LTH fetuses underwent surgical implantation of vascular catheters (n = 6 for each group). Five days after surgery, maternal and fetal arterial blood samples were collected for leptin, insulin, and glucose analysis. Placental tissue, periadrenal fat, and fetal hypothalami and adrenal glands were collected from additional control (n = 7) and LTH (n = 8) fetuses for analysis of leptin mRNA by quantitative, real-time, RT-PCR (qRT-PCR). There was a significant (P < 0.03) elevation in fetal plasma leptin in the LTH fetuses (3.5 ± 0.7 ng/ml) vs. control (1.1 ± 0.1 ng/ml). There were no differences in either glucose or insulin concentrations between the two groups. Periadrenal adipose leptin mRNA was significantly higher in the LTH group compared with control, as was placental leptin expression. The levels of leptin mRNA in adipose were ∼70 times higher vs. placenta. LTH significantly reduced expression of OB-Ra (short-isoform) in the hypothalamus (P = 0.0156), while resulting in a significant increase in adrenal OB-Rb (long-form) expression (P < 0.03). Our data suggest that leptin is a hypoxia-inducible gene in the ovine fetus and OB-R expression is altered by LTH. These changes may be responsible in part, for our previously observed alterations in fetal hypothalamic-pituitary-adrenal function following LTH.