Taken together, these results show that E2 stimulates the expression of iNOS/eNOS in neonatal and adult cardiomyocytes in-vivo and in-vitro. These novel findings provide a potential mechanism of how estrogen may modulate NOS expression and NO formation in the myocardium.

Cardiac myocytes contain functional estrogen receptors, however, the effect of estrogen on growth-related signaling pathways such as mitogen-activated protein kinases (MAPK) in the pathogenesis of cardiac disease is unclear. MAPKs are critically involved in regulatory signaling pathways which ultimately lead to cardiac hypertrophy. Here we show that 171]-estradiol (E2) activates extracellular signal-regulated kinase (ERKI/2), c-Jun-NHz-terminal protein kinase (JNK) and p38 in rat cardiomyocytes in a distinctive pattern. As shown by immunoblot analysis and phosphorylation assays, E2 (10 9 M) induced a rapid and transient activation of ERKI/2 and a rapid but sustained increase of JNK phosphorylation. In contrast, E2 had only a marginal effect on p38 activation. Furthermore, MAPK phosphatase expression was induced by E2 and E2-stimulated expression of endothelial and inducible NO synthase was inhibited by PD 98059, an inhibitor of the ERK pathway. These novel observations may help to explain the role of estrogen in gender-based differences found in cardiac disease.