Insulin-Like Growth Factor-I (IGF-I) is a potent mitogenic peptide produced by many cell types in mammals. In the adult, IGF-I synthesis is under control of pituitary GH and its receptor (GHr). GHr expression during fetal life is minimal and tissue specific. GHBP is a carrier protein for GH and is structurally related to GHr. Expression of GHBP and GHr are, in part, related to nutritional sufficiency in the adult, but in the neonate those factors controlling synthesis are unclear. We explored the hypothesis that GHr and GHBP are expressed in liver and intestine from suckling rats and that their expression is altered by tasting. Method: suckling rats (n=18) of 10-12 d age, either dam fed or fasted for 12 hours, were killed and intestine and liver then removed. Blood was also obtained for GHBP assay using a specific immunoassay. The presence of GHr and GHBP specific mRNA 's in liver and proximal jejunum and ileum were determined using reverse transcription (RT) of extracted RNA into cDNA, followed by the polymerase chain reaction (PCR), using rat specific primers. Results: RT-PCR on specimens from dam fed animals showed the presence of GHr specific mRNA in liver and proximal, but not distal, small bowel. The intensity of the band for GHr from liver but not intestine was diminished from fasted sucklings. RT-PCR in these same animals also detected the presence of GHBP- specific mRNA in liver, proximal and mid jejunum and ileum. The intensity of the band for GHBP from liver and intestine was diminished from fasted sucklings compared to dam fed animals. Serum GHBP concentration from dam fed animals was 347 50 pM. GHBP levels in fasted animals were significantly lower (18329 pM, p<0.01 from dam fed) and mirrored the decrease in band intensity seen using RT-PCR. Conclusion: Both Ghr and GHBP mRNA's are expressed in suckling liver and intestine and may play roles in local regulation pf IGF-I synthesis. Changes in synthesis with fasting in the neonate are suggested from this work.
|Original language||English (US)|
|Journal||Journal of Investigative Medicine|
|State||Published - Feb 1999|
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)