Leptin in the ovine fetus correlates with fetal and placental size

Objective: The purpose of this study was to detect the presence of leptin and its receptor in ovine fetal tissues and to examine the relationship between circulating leptin concentrations and fetal and placental weights on gestational day 138 (GD138) of ovine pregnancy (term, 145 days). Study Design: Pregnant sheep (n = 18) were instrumented on GD 110 to facilitate measurement and chronic reduction of uterine blood flow and produce intrauterine growth restriction. Four animals that served as controls were euthanized on GD 138 to obtain fetal tissues to determine the presence of ovine leptin and its receptor by reverse transcriptase–polymerase chain reaction. Seven instrumented animals were randomized into the control group, and 7 instrumented animals were randomized into the uterine blood flow restricted group (reduction equaled approximately 50% on GD 138). Maternal and fetal blood samples were obtained on day 138 to measure plasma leptin concentrations, and animals were euthanized for the determination of fetal morphometrics and placental weight. Results: Expression of RNA for ovine leptin and its receptor were observed in fetal liver, skeletal muscle, kidney, heart, and placenta. Fetal body weight, ponderal index, and placental weight were significantly decreased by approximately 40% in the blood flow restricted group as compared with controls. Fetal leptin concentrations were increased by 45% in the uteroplacental blood flow restricted group (P = .01). Maternal leptin concentrations were not significantly different between the 2 groups and did not correlate with fetal concentrations. Fetal leptin concentrations had an inverse relationship with uterine blood flow (r = -0.73; P = .004), fetal body weight (r = -0.78; P = .002), and placental weight (r = -0.68; P = .01). Conclusion: Ovine fetal tissues express RNA for leptin and its receptor. Circulating leptin concentrations in the ovine intrauterine growth restriction fetus were significantly elevated on gestational day 138 compared with controls. Fetal leptin concentrations were inversely related to uterine blood flow and fetal and placental weight. These findings suggest that fetal leptin may be involved in an adaptive response to intrauterine growth restriction. (Am J Obstet Gynecol 2001;185:786-91.)