Aim To observe the effects of lysophosphatidic acid(LPA) on system generation of adrenomedullin(ADM) with its receptors:calcitonin receptor like receptor(CRLR) and receptor activity modifying protein(RAMP),and the effects of ADM on proliferation of the vascular smooth muscle cells(VSMC) induced by LPA.Methods VSMC of rat aortic were cultured by explant method.DNA synthesis of VSMC were measured by 3H-TdR incorporation.The ADM concentration in VSMC were determined by radioimmunoassay.Results LPA stimulated the production of ADM on vascular smooth muscle cells in rats.LPA up-regulated the expression of mRNA of ADM and its receptors CRLR,RAMP2 and RAMP3 in VSMC.ADM can inhibit 3H-TdR incorporation of rat VSMC stimulated by LPA.ADM inhibited activation of mitogen-activated protein kinase(MAPK) in VSMC induced by LPA.Conclusions ADM and its receptors inhibit VSMC proliferation which involves in its inhibition on MAPK activity.