Dopamine receptors exist in many tissues, including rat cardiac tissue. However, the physiological importance of dopamine receptors in the homeostatic regulation of cardiac function is unclear. In this study, a model of ischaemia/ reperfusion was established by culturing primary neonatal rat cardiomyocytes in ischaemia-mimetic solution for 2 hr, followed by incubation in normal culture medium for 24 hr. Lactate dehydrogenase activity, superoxide dismutase activity and malondialdehyde content were determined colorimetrically with a spectrophotometer. Apoptotic cell death was assayed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling staining and flow cytometry, and morphological alterations were observed with transmission electron microscopy. The intracellular free calcium concentration ([Ca 2+ ] i ) was measured by confocal laser scanning microscopy. Finally, the expression of dopamine receptor 1 (DR1), caspase-3, -8 and -9, Fas, Fas ligand and Bcl-2 and the release of cytochrome c were analysed by Western blot. The results showed that DR1 expression was increased markedly during ischaemia/reperfusion. Treatment with 10 μ M SKF-38393 (DR1 agonist) significantly increased lactate dehydrogenase activity, decreased superoxide dismutase activity and increased malondialdehyde content in the culture medium. The DR1 agonist promoted the release of cytochrome c , accumulation of [Ca 2+ ] i , and apoptosis induced by ischaemia/reperfusion. Furthermore, SKF-38393 up-regulated the expression of caspase-3, -8 and -9, Fas and Fas ligand, and down-regulated Bcl-2 expression. In contrast, 10 μ M SCH-23390 (DR1 antagonist) had no significant effects on the above indicators. In conclusion, DR1 activation is involved in the apoptosis of cultured neonatal rat cardiomyocytes in simulated ischaemia/ reperfusion through the mitochondrial and death receptor pathways.Ischaemia/reperfusion injury is a major cause of morbidity and mortality in many diseases such as stroke, myocardial infarction and acute renal tubular necrosis. Ischaemic conditions result in ATP depletion and accumulation of toxic metabolites. Reperfusion causes production of reactive oxygen intermediates [1]. These alterations contribute to ischaemia/reperfusion injury, which is characterized by the presence of necrotic and apoptotic areas in the affected organs [1,2]. Apoptosis has been recognized as a cellular mechanism of myocardial ischaemia/reperfusion injury. Dopamine receptors belong to the G protein-coupled receptor family [3]. Five distinct dopamine receptors have been isolated, characterized and divided into two subfamilies, D1-and D2-like receptors, on the basis of their biochemical and pharmacological properties. The D1-like subfamily is composed of D1 and D5 receptors, and the D2-like subfamily includes D2, D3 and D4 receptors [4] Dopamine receptors not only are abundant in brain tissue but also exist in cardiac tissue [7]. A selective D1-like rec...
