EXPRESSION OF GROWTH-HORMONE RECEPTOR IN THE BOVINE MAMMARY-GLAND DURING PRENATAL DEVELOPMENT

Growth hormone (GH) is known to play a key role in postnatal growth an d differentiation. The role of GH and its receptor (GHR) in prenatal d evelopment, however, is still controversial. Using reverse transcripti on polymerase chain reaction (RT-PCR), in situ hybridization (ISH) and immunohistochemistry we demonstrated the presence of GHR mRNA and pro tein in bovine mammary glands during fetal development. RT-PCR reveale d GHR transcripts in fetal mammary glands from the third to the ninth month of pregnancy. By non-radioactive ISH, GHR mRNA was localized in the glandular epithelium, the surrounding mesenchymal cells, endotheli al cells of vessels and in the stratum basale of the epidermis of feta l mammary glands. From the sixth month of fetal life onwards, GHR tran scripts were also found in the cytoplasm of adipocytes. Immunohistoche mical studies using the monoclonal antibody mAb 263 revealed the same distribution pattern as the mRNA. Our results imply that the growth ho rmone receptor is distinctly expressed in the immature mammary gland, suggesting that GH is involved in growth and differentiation of the fe tal mammary gland.