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Abstract. We investigated whether increased contractile responsiveness to epidermal growth factor (EGF) is associated with altered activation of mitogen-activated protein kinase (MAPK) in the aortic smooth muscle of deoxycorticosterone acetate (DOCA)-salt hypertensive rats. EGF induced contraction and MAPK activity in aortic smooth muscle strips, which were significantly increased in tissues from the DOCA-salt hypertensive rats compared with those from shamoperated rats. AG1478, PD98059, and LY294002, inhibitors of EGF receptor (EGFR) tyrosine kinase, MAPK/ extracellular signal-regulated kinase (ERK) kinase, and phosphatidylinositol 3-kinase (PI3K), respectively, inhibited the contraction and the activity of ERK1 / 2 that were elevated by EGF. Y27632 and GF109203X, inhibitors of Rho kinase and protein kinase C, respectively, attenuated EGF-induced contraction, with no diminution of ERK1 / 2 activity. Although EGF also elevated the activity of EGFR tyrosine kinase in both sham-operated and DOCA-salt hypertensive rats, the expression and the magnitude of activation did not differ between strips. These results strongly suggest that EGF induces contraction by the activation of ERK1/ 2, which is regulated by the PI3K pathway in the aortic smooth muscle of DOCA-salt hypertensive rats.

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