Expression of the growth hormone-binding protein messenger RNA in the liver and extrahepatic tissues in the rat: co-expression with the growth hormone receptor.

A cDNA encoding a growth hormone-binding protein (GH-BP) was recently cloned from mouse and rat liver. The GH-BP in these species is identical to the extracellular part of the GH receptor (GH-R) with the transmembrane and intracellular domain substituted for a hydrophilic tail. In the present study the expression of the GH-BP and GH-R was studied in rat liver and extrahepatic tissues. Specific transcripts with estimated sizes of 1.2 kb (GH-BP) and 4.0 kb (GH-R) were found in the liver from both sexes. The expression of GH-BP increased with age up to puberty suggesting that it is developmentally regulated in a similar manner as GH-R. GH-BP mRNA was found in all extrahepatic tissues examined that contained GH-R mRNA. The ratio between the 1.2 kb and 4.0 kb transcripts varied between tissues indicating that GH-R and GH-BP transcripts may be separately regulated. The co-expression of GH-BP and GH-R suggests a functional role for the GH-BP in the local regulation of GH action.