Effect of IGF-I on serine metabolism in fetal sheep

Acute infusion of IGF-I to the fetus has been shown to inhibit amino acid o xidation and appears to increase fetoplacental amino acid uptake. This stud y was designed to investigate further the effects of IGF-I on fetal amino a cid metabolism. Radiolabeled serine was used to test the hypothesis that fe tal IGF-I infusion enhances serine uptake into the fetus and/or placenta an d inhibits serine oxidation. Eight fetal sheep were studied at 127 days of gestation before and during a 4-h infusion of IGF-I (50 mu g/h per kg). During the infusion there was no change in uptake of serine or its oxidation by fetus or placenta. However, both uptake and oxidation of serine and glycine decreased in the fetal car cass. There was also a decrease in fetal blood serine and glycine concentra tions which could indicate a decrease in protein breakdown, although reduce d amino acid synthesis cannot be excluded. Thus IGF-I appeared to influence the distribution of these amino acids as oxidative substrates between diff erent fetal tissues. In addition, fetal IGF-I infusion increased the conver sion of serine to glycine which is Likely to have increased the availabilit y of one-carbon groups for biosynthesis. Our data provide further evidence that IGF-I plays a role in the regulation of fetoplacental amino acid metab olism.