Abstract: AIM: To study the mechanisms of effects of the κ-opioid receptor (κ-OR) on neonatal rat hypertrophic myocardial cells induced by isoproterenol (ISO). METHODS: Myocardial cells of neonatal rats were cultured in vitro.The total protein content was detected by the Lowry's assay.The volume of myocardial cell was measured by computer photogragh analysis system and the protein synthesis was assayed with [³H] leucine intake method.The degree of extracellular signal-regulated kinase (ERK) phosphorylation was determined by western- blotting.RESULTS: U0126(an inhibitor of ERK) decreased the total protein content, the cell size, the[³H] leucine incorporation and the ERK phosphorylation degree in hypertrophic myocardial cells induced by ISO.1 μmol/L U50, 488H(a κ-opioid receptor antagonist) could decrease the total protein content, the cell size, the[³H] leucine incorporation and the degree of ERK phosphorylation.But these effects could be diminished when incubated with U0126. CONCLUSION: κ-opioid can abolish the hypertrophic response induced by ISO of cardiac myocytes, which was associate with ERK pathway.The inhibitor of ERK significantly inhibits the ISO-induced hypertrophied effect.

Key words: κ-opioid, β-receptor, myocardial hypertrophy, extracellular signal-regulated kinase