p38 MAPK-dependent eNOS upregulation is critical for 17β-estradiol- mediated cardioprotection following trauma-hemorrhage

Studies have shown that p38 MAPK and nitric oxide (NO), generated by endothelial NO synthase (eNOS), play key roles under physiological and pathophysiological conditions. Although administration of 17β-estradiol (E₂) protects cardiovascular injury from trauma-hemorrhage, the mechanism by which E₂ produces those effects remains unknown. Our objective was to determine whether the E₂-mediated activation of myocardial p38 MAPK and subsequent eNOS expression/phosphorylation would protect the heart following trauma-hemorrhage. To study this, male Sprague-Dawley rats underwent soft-tissue trauma (midline laparatomy) and hemorrhagic shock (mean blood pressure 35-40 mmHg for 90 min), followed by fluid resuscitation. Animals were pretreated with specific p38 MAPK inhibitor SB-203580 (SB; 2 mg/kg), and nonselective NO synthase inhibitor N^G-nitro-L-arginine methyl ester (L-NAME; 30 mg/kg) 30 min before vehicle (cyclodextrin) or E₂ (100 μg/kg) treatment, followed by resuscitation, and were killed 2 h thereafter. Cardiovascular performance and other parameters were measured. E₂ administration following trauma-hemorrhage increased cardiac p38 MAPK activity, eNOS expression and phosphorylation at Ser¹¹⁷⁷, and nitrate/nitrite levels in plasma and heart tissues; these were associated with normalized cardiac performance, which was reversed by SB administration. In addition, E₂ also prevented trauma-hemorrhage-induced increase in cytokines (IL-6 and TNF-α), chemokines (macrophage inflammatory protein-2 and cytokine-induced neutrophil chemoattractant-1), and ICAM-1, which was reversed by L-NAME administration. Administration of E₂ following trauma-hemorrhage attenuated cardiac tissue injury markers, myeloperoxidase activity, and nitrotyrosine level, which were reversed by treatment with SB and L-NAME. The salutary effects of E₂ on cardiac functions and tissue protection following trauma-hemorrhage are mediated, in part, through activation of p38 MAPK and subsequent eNOS expression and phosphorylation.