No abstract

Earlier, we reported that second trimester human fetal kidney and, to a much lesser extent, human fetal liver were capable of synthesizing and secreting the beta-subunit of hCG. Recently, we also have shown that these tissues, likewise, synthesize and secrete the alpha-subunit of hCG. The hCG produced is biologically active. To determine the cellular localization of these peptides, immunocytochemical studies were performed on human fetal tissues using antibodies against beta hCG, alpha hCG, and the intact hormone. Placental syncytiotrophoblast served as an immunopositive control. In the human fetal kidney, the ascending (thick) limb of the loop of Henle, distal convoluted tubule, and occasional cells in the collecting ducts were distinctly immunopositive for both beta hCG and the alpha-subunit. Small amounts of light positive staining occurred in only a few hepatocytes. Placental syncytiotrophoblast was routinely positive for both subunits, but fetal lung and striated muscle were negative. These immunocytochemical results indicate that immunoreactive beta hCG as well as the alpha-subunit are present in placental syncytiotrophoblast, in the distal renal nephron, and in a limited population of hepatocytes. The qualitative number and intensity of immunopositive cells closely correlate with the quantitative amounts of their hCG subunit synthesis. Taken together with our previous biosynthetic data, the immunocytochemical localization reported here indicates the probable cellular sites of alpha- and beta hCG synthesis in these tissues. The presence of comparable alpha- and beta-subunit staining in identical cell populations suggests that both hCG subunits and, therefore, perhaps intact hCG are produced at these same cellular sites during fetal life.

The kidney, and to a slight extent the liver, of human fetuses were found to synthesize and secrete the alpha subunit common to glycoprotein hormones. Fetal lung and muscle did not synthesize this protein. Since fetal kidney and liver were previously found to synthesize beta chorionic gonadotropin, their ability to synthesize bioactive chorionic gonadotropin was also determined. The newly synthesized hormone bound to mouse Leydig cells and elicited a biological response: namely, the synthesis of testosterone. These results suggest that the human fetus may participate in metabolic homeostasis during its development.