In this study, we demonstrate production and secretion of adrenomedullin (AM) from cultured vascular smooth muscle cells (VSMCs). In addition to endothelial cells (ECs), we found immunoreactive (ir-) AM in culture media of rat and bovine VSMCs in the survey for AM-producing cells. Although the secretion level of ir-AM was at most 1/6 that of rat ECs, all the examined VSMCs were shown to produce AM. By gel filtration, reverse phase high-performance liquid chromatography, and biological characterization, ir-AM in the culture medium was identified to be rat AM of 50 residues. By RNA blot analysis, a positive band of AM mRNA was detected in cultured VSMC at an intensity 3-4 fold higher than that in adrenal gland. Gene expression and production of AM were markedly augmented by tumor necrosis factor-alpha. Based on these data as well as the presence of AM specific receptors on VSMCs, AM secreted from VSMC is deduced to function as an autocrine or paracrine regulator in vascular cell communication.