Increased secretion of adrenomedullin from cultured human astrocytes by cytokines

Adrenomedullin, originally discovered from pheochromocytoma, is a member of the calcitonin gene-related peptide family. The production and secretion o f adrenomedullin by cultured human astrocytes were studied by northern blot analysis and radioimmunoassay. Northern blot analysis showed the expressio n of adrenomedullin mRNA in cultured human astrocytes. Immunoreactive adren omedullin concentrations in the culture medium were 29.6 +/- 1.2 fmol/10(5) cells/24 h (mean +/- SEM, n = 4). Treatment with interferon-gamma (100 U/m l), tumor necrosis factor-alpha (1 and 10 ng/ml), or interleukin-1 beta (1 and 10 ng/ml) for 24 h caused >20-fold increases in immunoreactive adrenome dullin levels in the culture medium of human astrocytes. On the other hand, northern blot analysis showed only small increases (similar to 40%) in the adrenomedullin mRNA expression of human astrocytes with either 100 U/ml in terferon-gamma or 10 ng/ml interleukin-1 beta and no noticeable change with tumor necrosis factor-alpha. Reverse phase HPLC of the medium extracts of human astrocytes treated with interferon-gamma, tumor necrosis factor-alpha , or interleukin-1 beta showed that most Of immunoreactive adrenomedullin w as eluted in the position of adrenomedullin-(1 -52). On the other hand, imm unoreactive adrenomedullin in the medium of human astrocytes without cytoki ne treatment was eluted earlier than the adrenomedullin standard, suggestin g that this immunoreactive adrenomedullin represents adrenomedullin with so me modifications or fragments of the adrenomedullin precursor. The present study has shown the production and secretion of adrenomedullin by human ast rocytes and increased secretion of adrenomedullin by cytokines.