Phenylephrine protects neonatal rat cardiomyocytes from hypoxia and serum deprivation-induced apoptosis

Previous studies have shown that alpha-adrenergic activation reduces myocardial damages caused by ischemia/reperfusion. However, the molecular mechanisms of how alpha-adrenergic activation protects the myocardium are not completely understood, The objective of this study was to test the hypothesis that alpha-adrenergic activation protects the myocardium by, at least in part, inhibiting apoptosis in cardiomyocytes. The current data has shown that apoptosis in neonatal rat cardiomyocytes, induced by 24 h treatment with hypoxia (95% N-2 and 5% CO2) and serum deprivation, was inhibited by co-treatment with phenylephrine, Pre-treatment with phenylephrine for 24 h also protected cardiomyocytes against subsequent 24 h treatment with hypoxia and serum deprivation, Exposure of cardiomyocytes to phenylephrine for up to 9 days under normoxic conditions did not cause apoptosis, The phenylephrine-mediated cytoprotection was blocked by an alpha-adrenergic antagonist, phentolamine, beta-adrenergic activation with isoproterenol did not protect cardiomyocytes against hypoxia and serum deprivation induced apoptosis, Under hypoxic conditions, phenylephrine prevented the down-regulation of Bcl-2 and Bcl-X mRNA/protein and induced hypertrophic growth. Phenylephrine mediated protection was abrogated by the phosphatidylinositol 3-kinase (PI 3-kinase) inhibitor wortmannin and was mimicked by the caspase-9 peptidic inhibitor LEHD-fmk, These results suggest that alpha-adrenergic activation protects cardiomyocytes against hypoxia and serum deprivation induced apoptosis through regulating the expression of mitochondrion-associated apoptosis regulatory genes, preventing activation of mitochondrial damage induced apoptosis pathway (cytochrome C-caspase-9), and activating hypertrophic growth.