Leptin mRNA was measured in adipose tissue of fetal sheep by reverse transcription polymerase chain reaction (RTPCR). Abundance of leptin mRNA relative to beta-actin mRNA in fetal perirenal adipose tissue increased (P<0.02) with gestation, being higher at 144 d (0.73+/-0. 10, n=5) than at 90-91 d (0.40 +/- 0.08, n=6) or 125 d (0.40 +/- 0. 04, n=5) gestation (term approximately 147- 150 d). There was a positive relationship between relative abundance of leptin mRNA (y) and fetal body weight (x) between 90 and 144 d gestation (r(2) =0.27, P<0.01). The slope of the linear dependence of leptin mRNA on fetal weight was 15-fold greater (P<0.001) at 90-91d (y = 2.81x - 1.1, n=6, r(2) =0.71, P<0.025) than between 125-144 d gestation (y = 0.195x - 0.15, n=16, r(2) =0.39, P<0.01). Thus the leptin synthetic capacity of fetal adipose tissue appears to increase in late gestation but this is accompanied by constraint of its sensitivity to fetal body weight. We hypothesise that leptin synthesis in fetal adipose tissue is related to fetal nutrient supply and growth rate.
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BS Yuen, IC McMillen, ME Symonds, and PC Owens
KL Gatford, IJ Clarke, MJ De Blasio, IC McMillen, S Robinson J, and JA Owens
Poor prenatal growth is associated with limited evidence of GH deficiency in adult humans, which may contribute to their increased risk of cardiovascular and metabolic disease. We therefore examined the effects of placental restriction of fetal growth (PR) on size at birth, neonatal fractional growth rate (FGR) and the circulating GH profile in adolescent and young adult sheep of both sexes. Moderate or severe PR decreased birth size and increased neonatal FGR of weight, crown-rump length and abdominal circumference. In adolescent males, mean and baseline GH concentrations correlated negatively and independently with birth weight and FGR of weight, and mean GH concentrations correlated negatively with current weight. In young adult males, mean GH concentrations correlated negatively and independently with birth shoulder height and FGR of shoulder height whilst, in young adult females, these correlations were positive. This suggests that restricted fetal growth and reduced neonatal growth rate in sheep are followed by elevated circulating GH in adolescent and adult males, but GH deficiency or increased GH clearance in adult females.