Somatomedin-C or insulin-like growth factor I (Sm-C/IGF-I) and insulin-like growth factor I1 (IGF-11) have been implicated in the regulation of fetal growth and development.In the present study 3ZP-labeled complementary DNA probes encoding human and mouse Sm-C/IGF-I and human IGF-I1 were used in Northern blot hybridizations to analyse rat Sm-C/IGF-I and IGF-I1 mRNAs in poly(A+) RNAs from intestine, liver, lung, and brain of adult rats and fetal rats between day 14 and 17 of gestation.In fetal rats, all four tissues contained a major mRNA of 1.7 kilobases (kb) that hybridized with the human Sm-CflGF-I cDNA and mRNAs of 7.5, 4.7, 1.7, and 1.2 kb that hybridized with the mouse Sm-C/IGF-I cDNA.Adult rat intestine, liver, and lung also contained these mRNAs but Sm-C/ IGF-I mRNAs were not detected in adult rat brain.These findings provide direct support for prior observations that multiple tissues in the fetus synthesize immunoreactive Sm-C/IGF-I and imply a role for Sm-C/IGF-I in fetal development as well as postnatally.The abundance of a 7.5-kb Sm-CflGF-I mRNA in poly(A+) RNAs from adult rat liver was 10-50-fold higher than in other adult rat tissues which provides further evidence that in the adult rat the liver is a major site of Sm-C/IGF-I synthesis and source of circulating Sm-C/IGF-I.Multiple IGF-I1 mRNAs of estimated sizes 4.7, 3.9, 2.2, 1.75, and 1.2 kb were observed in fetal rat intestine, liver, lung, and brain.The 4.7-and 3.9-kb mRNAs were the major hybridizing IGF-I1 mRNAs in all fetal tissues.Higher abundance of IGF-I1 mRNAs in rat fetal tissues compared with adult tissues supports prior hypotheses, based on serum IGF-I1 concentrations, that IGF-I1 is predominantly a fetal somatomedin.IGF-I1 mRNAs are present, however, in some poly(A+) RNAs from adult rat tissues.The brain was the only tissue in the adult rat where the 4.7-and 3.9kb IGF-11 mRNAs were consistently detected.Some samples of adult rat intestine contained the 4.7-and 3.9-kb IGF-I1 mRNAs and some samples of adult liver and lung contained the 4.7-kb mRNA.These findings

Somatomedin-C/insulin-like growth factor-I and insulin-like growth factor-II mRNAs in rat fetal and adult tissues.