Endocrine Abstracts

Introduction: In sheep, modest maternal nutrient restriction over the period of rapid placental growth restricts placentome growth. Maternal plasma IGF-I concentration is unaffected but effects on placental IGF-I receptor mRNA expression are not known.

Methods: Twenty singleton-bearing ewes of similar body weight and parity were entered into the study. Ten ewes consumed 60% of their total energy requirements (i.e. nutrient restricted, NR) from 28 to 80 days gestation and ten consumed 150% of their total energy requirements (i.e. controls, C). All ewes were then fed 150% of their total energy requirements up to 140 days gestation. Placental tissue was sampled after euthanasia from both NR and C ewes at either 80 or 140 days gestation (n= 4-6 per group). Total RNA was extracted. IGF-I receptor mRNA abundance was examined by RT-PCR, using oligonucleotide primers specific to the IGF-I receptor (forward 5'-GCCTCCAACTTTGTCTTTGC-3' and reverse 5'-GCTGAAATACTCCGGGTTCA-3'). Results, in arbitrary units (a.u.; mean plus/minus s.e.m) are a ratio of an 18S rRNA internal control.

Results: At 80 days gestation nutrient restriction resulted in reduced IGF-I receptor mRNA (C: 77.7 plus/minus 9.0; NR: 53.1 plus/minus 2.2 a.u. (P< 0.05)) when placental weight was also decreased. By 140 days gestation these differences had been negated (C: 80.6 plus/minus 12.2; NR: 71.2 plus/minus 3.4 a.u.).

Conclusion: Maternal nutrient restriction restricts placental growth and IGF-I receptor mRNA abundance, an effect no longer apparent following nutrient restoration. The extent to which such a reduction in placental IGF-I receptor expression may influence nutrient partitioning to the developing fetus remains to be established.