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Background: Myocardial ischemia/reperfusion injury is the major cause of morbidity and mortality for cardiovascular diseases. Dopamine D2 receptors are expressed in cardiac tissues. However, the roles of dopamine D2 receptors in myocardial ischemia/reperfusion injury and cardiomyocyte apoptosis are unclear. Here we investigated the effects of both dopamine D2 receptors agonist (bromocriptine) and antagonist (haloperidol) on apoptosis of cultured neonatal rat ventricular myocytes induced by ischemia/reperfusion injury. Methods: Myocardial ischemia/reperfusion injury was simulated by incubating primarily cultured neonatal rat cardiomyocytes in ischemic (hypoxic) buffer solution for 2 h. Thereafter, these cells were incubated for 24 h in normal culture medium. Results: Treatment of the cardiomyocytes with 10 μM bromocriptine significantly decreased lactate dehydrogenase activity, increased superoxide dismutase activity, and decreased malondialdehyde content in the culture medium. Bromocriptine significantly inhibited the release of cytochrome c, accumulation of [Ca2+]i, and apoptosis induced by ischemia/reperfusion injury. Bromocriptine also down-regulated the expression of caspase-3 and -9, Fas and Fas ligand, and up-regulated Bcl-2 expression. In contrast, haloperidol (10 μM) had no significant effects on the apoptosis of cultured cardiomyocytes under the aforementioned conditions. Conclusions: These data suggest that activation of dopamine D2 receptors can inhibit apoptosis of cardiomyocytes encountered during ischemia/reperfusion damage through various pathways. [ABSTRACT FROM AUTHOR]

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 ([Ca2+]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 µM 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 [Ca2+]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 µM 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. [ABSTRACT FROM AUTHOR]