Growth hormone (GH) receptors are expressed on human fetal mesenchymal tissues--identification of messenger ribonucleic acid and GH-binding protein.

The role of GH in the fetus remains unclear, in spite of high circulating levels. In order to determine potential sites of action of GH in the human fetus, we have used a combination of immunocytochemistry and northern blotting to examine human fetal tissues for GH receptor or binding protein and its messenger RNA. Human fetal abortus tissues of 15-20 weeks gestation were obtained for sternum and skin. Decalcified paraffin sections, were prepared for immunostaining with a monoclonal antibody to the GH receptor or control antibodies. Chondrocytes were digested from sternum and costal cartilage for primary culture in monolayers for up to 14 days. Skin fibroblasts were similarly cultured and studied at passages 5-10. Polyadenylated mRNA was prepared from cultured chondrocytes and fibroblasts for subsequent northern blotting with a complementary DNA probe to the hGH receptor. Positive immunostaining for GH receptor was seen in growth plate, including chondrocytes in the proliferative and hypertrophic zones, perichondrium, osteoblasts, and erythroid precursor cells. GH receptor immunostaining was also seen in skin sections throughout epidermis, including sebaceous and sweat glands, and vessels and fibroblasts in the dermis. Cultured chondrocytes showed patchy staining, with colonies of immunopositive cells proliferating in culture. Skin fibroblasts showed uniform GH receptor immunostaining. Control sections and cultured cells did not stain. Cultured chondrocytes showed specific binding of 125I-hGH(1-3%), with a typical displacement curve for GH receptor. As for immunostaining, binding increased with time in culture. Finally, northern blotting revealed a single 5.1 kilodalton band representing GH receptor mRNA in both chondrocytes and skin fibroblasts. This study has demonstrated the presence of GH receptor protein and mRNA on human fetal tissues including growth plate chondrocytes and osteoblasts, as well as skin epidermal structures and dermal fibroblasts. These receptors are capable of binding hGH, raising the possibility that, in contrast to current dogma, GH receptors play a functional role in the human fetus by 15 weeks gestation.