Induction of adrenomedullin by hypoxia in cultured retinal pigment epithelial cells

PURPOSE. To explore the effects of hypoxia on the production and secretion of adrenomedullin (ADM) and endothelin (ET)-1 in human retinal pigment epit helial (RPE) cells. METHODS. RPE cells were cultured under normoxic or hypoxic (1% O-2) conditi ons. Expression of ADM and ET-1 was examined by Northern blot analysis and radioimmunoassay. Effects of ADM and ET-1 on the number of RPE cells were e xamined by modified 3-(4,5-dimetylthiazol-2-yl)-2,5-diphenyltetrazolium bro mide (MTT) assay. RESULTS. ADM mRNA expression levels and immunoreactive ADM levels in the me dium were increased by hypoxia in all three human RPE cell lines (ARPE-19, D407, and F-0202). Immunoreactive ET was detected in the cultured media of D407 cells and ARPE-19 cells and identified as ET-1 by reversed-phase high performance liquid chromatography. Hypoxia treatment for 48 hours increased immunoreactive ET levels approximately 1.3-fold in the cultured media of D 407, but not ARPE-19 cells. Hypoxia decreased the number of ARPE-19 cells a nd F-0202 cells, and the treatment with ADM ameliorated the hypoxia-induced decrease in the cell number. In contrast. exogenously added ET-1 had no si gnificant effects on the number of ARPE-19 cells under normoxia and hypoxia . CONCLUSIONS. Hypoxia increased the expression of ADM in all three human RPE cell lines, whereas the induction of ET-1 by hypoxia was found only in D40 7 cells. ADM induced by hypoxia may have protective roles against hypoxic c ell damage in RPE cells.