Department of Cardiovascular Biology, Rhone-Poulenc Rorer Research and Development, Collegeville, PA 19426, USA

Correspondence to: H Zhu, Collateral Therapeutics, Inc. Research Center, Suite 100, 11025 Roselle Street, San Diego, CA 92121, USA. Fax: (858) 404-9350; E-mail: hzhu@collateralthx.com

Edited by CJ Thiele

Previous studies have shown that -adrenergic activation reduces myocardial damages caused by ischemia/reperfusion. However, the molecular mechanisms of how -adrenergic activation protects the myocardium are not completely understood. The objective of this study was to test the hypothesis that -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% N₂ 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 -adrenergic antagonist, phentolamine. -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 -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. Cell Death and Differentiation (2000) 7, 773-784

apoptosis; adrenergic; cardiomyocytes; hypertrophy; ischemia

ANF, atrial natriuretic factor; ISO, isoproterenol; LIF, leukemia inhibitory factor; MM, minimal medium; NO, nitric oxide; PARP, poly-adenyl ribose transferase; PE, phenylephrine; PHE, phentolamine; PI, posphoinositol; PM, plating medium