TISSUE-SPECIFIC DEVELOPMENTAL REGULATION OF THE MESSENGER RIBONUCLEIC-ACIDS ENCODING THE GROWTH-HORMONE RECEPTOR AND THE GROWTH-HORMONE BINDING-PROTEIN IN RAT FETAL AND POSTNATAL TISSUES

Tissue responsiveness to growth hormone is likely to be regulated by local concentrations and availability of the membrane-bound growth hormone receptor (GHR) and perhaps by the actions of the soluble growth hormone binding protein (GHBP). To determine whether the developmental regulation of the GHR and GHBP might vary among tissues, we have measured the relative abundance of the 4.3-kb GHR and 1.3-kb GHBP mRNA in rat fetal and postnatal liver, kidney, lung, and ileum by Northern hybridization of polyadenylated RNA with a P-32-labeled antisense riboprobe prepared from a rat GHR cDNA. The GHR and GHBP mRNA were both present in the four tissues studied at fetal age 19 d (E19). In postnatal liver, both transcripts increased in abundance 3- to 4-fold after 14 d to mature levels at 42 d (p = 0.0001). Similar changes were seen in postnatal kidney for GHR mRNA abundance; however, GHBP mRNA abundance increased only 2- to 3-fold to mature levels by 28 d (kidney GHR versus GHBP mRNA profile, p = 0.0001). In lung, a 2-fold linear increase in GHR mRNA abundance was observed (p = 0.0019), but the GHBP mRNA did not change (GHR versus GHBP mRNA profile, p = 0.0006). Both transcripts decreased in abundance by 2- to 3-fold from E19 to 42 d in ileum (p < 0.05). The abundance of both transcripts was three to 10 times greater in 60-d liver than in the other three tissues at 60 d. The variation in abundance and in the developmental profiles of the GHR and GHBP mRNA observed in these fetal and postnatal tissues suggests that the GHR and GHBP could mediate differences within and between tissues in the responsiveness to growth hormone. The differential regulation of the two transcripts evident in kidney and lung supports the emerging evidence that the GHBP may have a function distinct from that of the GHR.