Growth hormone-releasing hormone (GH-RH) can stimulate not only growth hormone (GH) secretion by anterior pituitary gland but also proliferation of many cancer cell lines in vitro and in xenografts tumor models in vivo. Several antagonists of GH-RH have been shown to inhibit several cancer growths, but the role of GH-RH antagonists in the regulation of neuroendocrine cancers cell proliferation and tumor progression remains obscure. The aim of the study was to evaluate the influence of JV-1-36 (synthetic GH-RH antagonist) on proliferation and VEGF secretion by human neuroendocrine lung non-small cell carcinoma (NCI-H727) using cell culture model. The in vitro effect of JV-1-36 on the proliferation of NCI-H727 cells was assessed by the measurement of BrdU incorporation by colorimetric immunoassay. The presence of VEGF and membrane GH-RH receptors on the surface of H727 cells were visualized by immunocytochemistry using specific anti-GH-RH receptor antibody directed to the carboxy-terminal region. VEGF secretion to the cell cultures supernatants was assessed by ELISA methods. Immunoreactive cell membrane GH-RH receptors and VEGF-immunopositive cytoplasmatic granules were clearly confined on the surface of nearly all cancer cells. JV-1-36 at the concentration of 10(-6)-10(-10)M significantly inhibited growth of H727 cells, compared with untreated controls. In H727 cells, the antiproliferative JV-1-36 effect was associated with a dose-dependent reduction of VEGF secretion. In conclusion, our findings demonstrate the strong evidence for the antiproliferative action of GH-RH antagonist JV-1-36 for the NCI-H727 cells. In addition the suppression of VEGF secretion by H727 cells might contribute, at least in part, to the antitumor action of GH-RH antagonists.