Although leptin is important in the control of appetite and energy expenditure in adulthood, its actions before birth are unclear. This study investigated the effects of leptin on hepatic carbohydrate metabolism and insulin signalling in fetal sheep. Twelve sheep fetuses were chronically-catheterised at 115120 d of gestation (term 145±2 d), and infused intravenously with saline (0.9% NaCl; n=6) or recombinant ovine leptin (0.51.0 mg/kg/d; Protein Laboratories Rehovot, Israel; n=6) for 5 d from 125 to 130 d. Arterial blood was collected daily from 2 d before and throughout infusion. At 130 d, ewes and fetuses were killed by sodium pentobarbitone administration, and fetal liver was frozen and stored at −80 °C. Hepatic glycogen content was measured enzymatically, and glucose-6-phosphatase activity was determined from phosphate production. Insulin signalling protein levels (insulin receptor β-subunit, IRβ; phosphatidylinositol-3-kinase subunits, p85 and P110β; phosphokinase C subunit, PKCζ) were determined by Western blot. Plasma leptin and insulin were measured using ovine-specific RIA and ELISA, respectively; plasma glucose was determined using an autoanalyser. Data (mean±S.E.M) were analysed by two-way ANOVA and t-test. On each infusion day, plasma leptin in the leptin-infused fetuses was higher than in the saline-infused fetuses. On the fifth day of infusion, plasma leptin in the leptin-infused fetuses (3.32±0.23 ng/ml) was significantly greater than in fetuses infused with saline (0.77±0.09 ng/ml, P<0.05). Plasma insulin and glucose did not differ between fetuses on any treatment day. Hepatic glycogen content and glucose-6-phosphatase activity in the leptin-infused fetuses (12.2±1.8 mg/g and 15.1±2.7 U/mg protein) were significantly lower than in the saline-infused fetuses (21.7±3.0 mg/g and 29.9±5.2 U/mg protein, P<0.05). There were no differences in hepatic insulin signalling protein levels between fetuses. Therefore, in fetal sheep, leptin suppresses hepatic glycogen deposition and glucose-6-phosphatase activity. These actions of leptin in utero do not appear to be mediated by changes in hepatic insulin signalling pathways. Funded by the BBSRC.
06 - 07 Nov 2006
Society for Endocrinology