Localization of the growth hormone receptor, identified by immunocytochemistry, in second trimester human fetal tissues and in placenta throughout gestation

Pituitary GH secretion appears largely unnecessary for the attainment of normal birth size in many species, including man. This is believed to be due to an immaturity and/or an absence of GH receptors in many fetal tissues. However, in vitro studies using late first trimester human fetal tissues have demonstrated mitogenic actions of GH on liver and stimulation of insulin biosynthesis in pancreas. To resolve this discrepancy, we have employed immunocytochemistry to identify the presence and distribution of GH receptors in various human fetal tissues. Fetuses of 14-16 weeks gestation were obtained after therapeutic abortion, tissues were fixed, and immunocytochemistry was performed using monoclonal antibodies against purified rat or rabbit GH receptor. The specificity of staining was confirmed by preabsorbtion of the antibodies with 1) adult rat liver membranes or 2) human fetal liver membranes, both of which possess specific GH-binding sites, or 3) human fetal skeletal muscle membranes, which do not specifically bind GH. Positive staining was seen in a subpopulation of liver parenchymal cells, in the ductal and endocrine tissue of pancreas, in the germinal layer of the epidermis and the deeper dermal layers of skin, and in the tubular epithelium of kidney. No immunopositive staining was seen in skeletal or cardiac muscle, epiphyseal growth plate, lung, intestine, or adrenal. Positive staining was present in the neuronal cell bodies of the cerebral cortex. GH receptor was also detectable as early as 8 weeks gestation in syncytial layers of the placenta and was maintained until term. Results demonstrate the presence of immunoreactive GH receptor/binding protein in some human fetal tissues early in development. In particular, these results would support a role for GH in the growth and function of liver and pancreas