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Sildenafil-mediated acute cardioprotection is independent of the NO/cGMP pathway

¹Division of Cardiology, Department of Medicine, and Department of Pathology, Albert Einstein College of Medicine, Bronx, New York; and ²Department of Molecular and Cellular Physiology, Louisiana State University Health Sciences Center, Shreveport, Louisiana

Submitted 24 March 2006 ; accepted in final form 27 August 2006

Sildenafil, a potent inhibitor of phosphodiesterase type 5, has recently been investigated in animal models of myocardial ischemia-reperfusion (MI/R) injury. Previous studies have suggested that the protective effects of sildenafil are mediated via activation of endothelial nitric oxide (NO) synthesis (eNOS) and inducible NOS (iNOS). To further investigate the protective mechanism of sildenafil, we subjected wild-type, eNOS, and iNOS null animals to 30 min of myocardial ischemia and 24 h of reperfusion. Treatment with 0.06 mg/kg sildenafil 5 min before reperfusion significantly reduced myocardial infarct size in wild-type, eNOS null mice (eNOS^–/–), and iNOS^–/– animals. Additionally, the low dose utilized in this study did not alter myocardial cGMP. These results suggest that acute low-dose sildenafil-mediated cardioprotection is independent of eNOS, iNOS, and cGMP. In a second series of experiments, we investigated sildenafil in db/db diabetic mice subjected to MI/R. We found that sildenafil failed to protect diabetic mice against MI/R. However, NO^· donor therapy was found to significantly protect against MI/R injury in both nondiabetic and diabetic mice, suggesting that protection could be conferred in diabetic mice and that the upstream modulator of soluble guanylyl cyclase, NO^·, may mediate protection independent of cGMP signaling. The present study suggests that further research is needed to delineate the precise mechanisms by which sildenafil exerts cardioprotection.

cyclic guanosine monophosphate; nitric oxide; diabetes mellitus; phosphodiesterase type 5; myocardial infarction; endothelial nitric oxide; inducible nitric oxide; db/db mouse

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