Hypoxia-induced adrenomedullin production in the kidney

Hypoxia-induced adrenomedullin production in the kidney.BackgroundAdrenomedullin (AM) is a newly discovered peptide that has a potent vasorelaxant activity. To investigate its potential roles in hypoxia-induced renal injury, we examined whether AM production in the kidney increased under hypoxic conditions.MethodsThe AM transcript levels in Madin-Darby canine kidney (MDCK) cells, rat vascular smooth muscle cells (VSMCs), and rat mesangial cells were assessed by Northern blot analyses under normoxic and hypoxic conditions. The AM peptide in culture media was measured by radioimmunoassay. The effects of hypoxia on accumulation of cAMP in VSMCs were also examined. The stability of AM transcripts under normoxic and hypoxic conditions was compared in the presence of actinomycin D. The effects of hypoxia on AM promoter activity was assessed by transient transfection assays using the AM promoter subcloned upstream of luciferase gene.ResultsThe expression of AM transcripts increased significantly in MDCK cells, rat VSMCs, and rat mesangial cells under hypoxic conditions without changes in the stability of AM transcripts; however, the AM promoter activity under hypoxia was not elevated significantly. The accumulation of AM peptide in culture media also increased significantly under hypoxic conditions in MDCK cells (2.2 ± 0.1 fmol/105 cells in normoxia vs. 3.5 ± 0.3 fmol/105 cells in hypoxia, 6hr after hypoxia induction, P < 0.001), and in rat VSMCs (5.5 ± 0.3 fmol/105 cells in normoxia vs. 7.8 ± 0.4 fmol/105 cells in hypoxia, 8hr after hypoxia induction, P < 0.01). Under hypoxic conditions, cAMP levels in rat VSMCs increased significantly compared with those under normoxic conditions (13.3 ± 1.4 pmol/well vs. 4.6 ± 0.4 pmol/well, P < 0.01).ConclusionsRenal parenchymal cells as well as renal vessels may produce AM under hypoxic conditions