GROWTH HORMONE-RELEASING HORMONE-LIKE MESSENGER-RIBONUCLEIC-ACID AND IMMUNOREACTIVE PEPTIDE ARE PRESENT IN HUMAN TESTIS AND PLACENTA

Although the sequence of human GH-releasing hormone (GHRH) has been determined, all of the information concerning gene expression has been based on pathological sources of ectopic GHRH, since the only established physiological source of GHRH in humans is the hypothalamus. We recently reported the presence of extrahypothalamic GHRH-like mRNA and immunoreactive material in rat testis and placenta. To determine if human testis and placenta also contain immunoreactive GHRH-like peptides, tissue extracts were analyzed using enzyme-linked immunosorbent assay methodology. Both tissues had detectable quantities of immunoreactive peptide recognized by a monoclonal antibody to synthetic human GHRH-(1-44) (testis, 2.4 ng/g tissue, 0.68 ng/mg protein; placenta, 2.6 ng/g tissue, 0.36 ng/mg protein). The origin of these peptides was confirmed by extracting total RNA from human testis and placenta, with analysis on Northern blots probed with riboprobes for rat hypothalamic GHRH cDNA and human pancreatic tumor GHRH cDNA. Human testis and placenta total RNA both contain an approximately 790-nucleotide RNA species similar in size to that reported in ectopic GHRH-producing human tumors. In addition, two larger hybridization signals were seen at 3000 and 4900 nucleotides. These data suggest that testis and placenta are extrahypothalamic sites of expression of the human GHRH gene. Normal expression of the GHRH gene in extrahypothalamic sites may include transcription of larger mRNA species than those observed in ectopic pathological sources of GHRH expression.