Insulin-like growth factor I promotes growth selectively in fetal sheep in late gestation.
Insulin-like growth factor I (IGF-I) is required for normal fetal growth and skeletal maturation in late gestation, because null mutations of the IGF-I gene in mice reduce fetal weight and retard ossification of bones. To determine if, conversely, increased abundance of IGF-I promotes fetal growth and skeletal maturation, fetal sheep were infused intravascularly with recombinant human IGF-I (n = 7) (26 +/- 3 micrograms. h-1.kg-1) from 120 to 130 days gestation and compared with controls (n = 15). IGF-I infusion increased plasma IGF-I concentrations by 140% (P = 0.002) and weights of fetal liver, lungs, heart, kidneys, spleen, pituitary, and adrenal glands by 16-50% (P < 0.05). Weights and/or lengths of the fetus, placenta, gastrointestinal tract, individual skeletal muscles, and long bones were unchanged by IGF-I. However, IGF-I increased the percentage of proximal epiphyses of long bones present (P < 0.05) and their cross-sectional areas by 15 to 38% (P < 0.05). These results show that IGF-I promotes growth of major fetal organs, endocrine glands, and skeletal maturation in vivo, consistent with IGF-I actively controlling and not merely facilitating fetal growth. The variable response of different tissues may partly reflect tissue specificity in growth requirements for additional factors.
Lok
F
F
Department of Obstetrics and Gynaecology, University of Adelaide, Australia.
Owens
J A
JA
Mundy
L
L
Robinson
J S
JS
Owens
P C
PC
D000818:Animals; D001846:Bone Development / Q000187:drug effects*; D005314:Embryonic and Fetal Development / Q000187:drug effects*; D005260:Female; D005312:Fetal Blood; D005333:Fetus / Q000033:anatomy & histology; D006801:Humans; D007328:Insulin / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000494:pharmacology*; D007335:Insulin-Like Growth Factor II / Q000032:analysis; D009141:Musculoskeletal System / Q000196:embryology; D010920:Placenta / Q000033:anatomy & histology; D011247:Pregnancy; D011994:Recombinant Proteins; D012756:Sheep / Q000196:embryology
D007328:Insulin; D011994:Recombinant Proteins; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II