THE EFFECTS OF OVINE PLACENTAL-LACTOGEN INFUSION ON METABOLITES, INSULIN-LIKE GROWTH-FACTORS AND BINDING-PROTEINS IN THE FETAL SHEEP

It has been suggested, but not shown, that in the fetus placental lact ogen (PL) may affect the regulation of the IGFs and fetal metabolism. To examine the effects of PL on the circulating concentrations of the IGFs, IGF-binding proteins (IGFBPs), glucose, free fatty acids (FFAs) and amino nitrogen (AN), we infused late gestation sheep fetuses with recombinant ovine PL (roPL). Five chronically-catheterised sheep fetus es were infused intravenously with three 24 h infusions of saline, roP L (100 mu g bolus then 500 mu g over 24 h) and then saline again. Feta l roPL infusion increased plasma oPL from 0.4+/-0.1 to 3.3+/-0.5 nM (m ean+/-S.E.M.; P<0.05; factorial analysis of variance and Scheffe's tes t). Fetal plasma IGF-I, IGF-II, insulin, FFAs and blood glucose were u naffected by the roPL infusion. Fetal plasma IGFBP-3, as measured by W estern ligand blotting, decreased by 30% during fetal roPL infusion wh ile other fetal plasma IGFBPs were unaffected. Fetal roPL infusion dec reased fetal blood AN from 7.3+/-0.5 to 6.6+/-0.2 mM (P<0.05). Materna l plasma IGF-I, IGF-II, IGFBPs, insulin, FFAs, blood glucose and AN we re unaffected by the fetal roPL infusion. Saline infusion had no effec t on any parameter. The data suggest that PL is not a significant dete rminant of plasma IGFs in the late gestation sheep fetus although ther e may be an indirect effect via alterations in levels of IGFBP-3. The effect of fetal roPL infusion on fetal blood AN concentrations may sug gest some role for PL in the regulation of fetal amino acid metabolism .