Chronic in vivo nitric oxide deficiency impairs cardiac functional recovery after ischemia in female (but not male) mice

Nitric oxide (NO) is an important regulator of cardiac function and plays a key role in ischemic cardioprotection. The role of chronic NO deficiency in coordinating ischemic vulnerability in female myocardium has not been established. The aim of this study was to determine the influence of chronic in vivo NO synthase inhibition in modulating ex vivo ischemia-reperfusion responses in female hearts (relative to males). Mice were subjected to L-NAME (L-N^G-Nitroarginine-methyl-ester) treatment in vivo for 8 weeks. Cardiac fibrotic, inflammatory and cardiomyocyte Ca^{2 +} handling related gene expression changes were assessed. Hearts were Langendorff-perfused, subjected to 20 min global ischemia with 45 min reperfusion. In response to this moderate ex vivo ischemic insult, hearts derived from L-NAME treated female animals exhibited increased incidence of reperfusion arrhythmias, diastolic abnormality and reduced contractile recovery in reperfusion. This differential response was observed even though baseline performance of hearts from L-NAME treated animals was not different to vehicle controls, myocardial inflammatory and fibrotic indices were similar in males and females and the systolic blood pressure effect of L-NAME administration was equivalent in both sexes. Evaluation of a subgroup of mice with cardiomyocyte specific mineralocorticoid receptor deletion suggests involvement of this receptor in NO-deficiency mediated responses. To examine underlying pre-disposing mechanisms, expression of a panel of candidate genes encoding proteins involved in electromechanical homeostasis (particularly relevant to ischemic challenge) was evaluated in normoxic myocardial tissues from the L-NAME- and vehicle-treated animals. Analysis revealed that L-NAME treatment in females selectively regulated expression of genes related directly and indirectly to cardiomyocyte Ca^{2 +} handling in a manner consistent with destabilization of Ca^{2 +} homeostasis and arrhythmogenesis. Our investigation provides new insight into the role of sustained decrease in NO bioavailability in determining distinctive female cardiac vulnerability to ischemic challenge.