Organ-specific expression pattern of the human growth hormone/placental lactogen gene-cluster in the testis.
In addition to testosterone, the essential paracrine factor for spermatogenesis, a number of potential auto/paracrine regulatory substances such as beta-endorphins, enkephalins, chorionic gonadotropin beta, growth hormone-releasing hormone (GHRH) and insulin-like growth factor I (IGF-I) have been identified in the testis of various mammalian species. The latter findings prompted us to investigate a possible eutopic production of GH, placental lactogen (PL) and PRL in human testes. Specific expression of testicular GH/PL mRNA (n = 20) was shown by reverse transcription-polymerase chain reaction (RT-PCR) using a pair of primers designed to non-selectively amplify any transcript of the five GH/PL genes (GH-N, GH-V, PL-A, PL-B, PL-L). In contrast to the classical sites of production, the pituitary (exclusively GH-N transcripts) and the placenta (PL-A/B > 99%, GH-V < 1%), radioactive semiquantitative restriction enzyme analysis of the PCR-products revealed, that the testis has its own organ-specific pattern of GH/PL gene expression: PL-A/B > GH-V > or = PL-L = GH-N. All three organs express the single PRL gene, and testis and placenta show the alternative splice variant GH-V2. Immunological analyses by immunofluorometric assays for hPL-A/B, hGH-N and hPRL, demonstrated significant amounts of protein hormones in all testicular cytosolic homogenates (means: hPL 1.0 ng/g, hGH 5.1 ng/g and hPRL 58.7 ng/g tissue wet weight). Most noteworthy, hPL serum levels in an elderly age-matched healthy subjects (n = 18) were < 0.02 ng/ml. The concept of purely endocrine functions of placental and pituitary-derived GH/PL needs to be reassessed, since human testicular synthesis of these molecules suggest auto/paracrine functions in the male reproductive tract.