Intermedin (IMD), a novel member of the adrenomedullin (AM) peptide family stimulates cAMP production through AM receptors in endothelial cells (EC). It was recently shown by us that manoeuvres increasing cAMP levels in EC from the coronary microvasculature causes failure of endothelial barrier function. Therefore, the effects of IMD on endothelial barrier function of coronary microvasculature was studied. In cultured EC from rat coronary microvasculature IMD (10nM) increased permeability (albumin flux) by 145 ± 7%, reduced isometric tension (force production of EC cultured on collagen gels) by 180 ± 6%, and phosphorylation of the regulatory myosin light chain by 65 ± 7%. IMD caused inhibition of RhoA and Rac1 (pull down assay), two key regulators of EC cytoskeleton. This inhibition was accompanied by disassembly of actin filaments and loss of cadherin from cell-cell contacts (confocal microscopy) leading to rapid stellation of EC. These IMD effects are blocked by PKI (peptide inhibitor of PKA).

Conclusion: These data demonstrate that IMD has opposing effects on EC from coronary microvasculature mediated by PKA. It can stabilize EC barrier by inactivation of the contractile apparatus. However, IMD destabilizes EC barrier through destruction of actin cytoskeleton and inhibition of RhoA and Rac1, which overrules its barrier stabilizing effect.