Progesterone preserves eNOS coupling and supports endothelium-dependent vasodilation in the pulmonary artery of female rats: a potential therapeutic strategy for pulmonary arterial hypertension

Abstract Background Pulmonary arterial hypertension (PAH) is a severe vascular disease characterized by pulmonary vascular remodeling, endothelial dysfunction, and enhanced vasoconstriction, leading to progressive pulmonary arterial pressure elevation, right ventricular failure, and death. Notably, females are more susceptible to PAH but have better prognoses than males, drawing attention to the role of female sex hormones. While estradiol (E2) has been extensively studied, the role of progesterone (P4) remains largely unexplored. Purpose This study investigates effects of P4 on pulmonary arterial endothelial function and its potential as a therapeutic strategy for PAH. Methods Female Sprague-Dawley rats underwent either progesterone receptor inhibition (Mifepristone, RU486) or ovariectomy (OVX) followed by physiological doses of E2 or P4 replacement. Additionally, a monocrotaline (MCT)-induced PAH model was used to evaluate progesterone's therapeutic effects. The experimental groups were as follows: Control, RU486, Sham, OVX, OVX+E2, and OVX+P4. Cardiac function was detected by Echocardiography. Pulmonary and right ventricular pressures was measured by a polyethylene catheter with a multi-lead physiological recorder. Vasodilation function was determined by DMT620 system. Oxidative stress was observed by Dihydroethidium (DHE) staining. eNOS-related protein expression was analyzed by Western blot (WB). Nitric oxide (NO) content in pulmonary artery (PA) was detected by Griess Reagent. Sapropterin dihydrochloride (6R-BH4) was used to promote eNOS re-coupling. Results RU486-treated rats showed a time-dependent increase in eNOS and Ser1177 phosphorylation but, paradoxically, impaired endothelium-dependent relaxation and NO content at 12 and 24 hours. Similarly, 5 days post-surgery, OVX and OVX+E2 rats showed the same pattern as RU486-treated rats. In contrast, OVX+P4 rats showed no significant difference from Sham rats, suggesting progesterone deficiency may induce eNOS uncoupling. Oral administration of 6R-BH4 reversed this impairment in OVX and OVX+E2 rats, and WB analysis showed a reduced eNOS dimer/monomer (D/M) ratio in OVX and OVX+E2 rats, restored in OVX+P4 rats, suggesting progesterone's role in preventing eNOS uncoupling. In MCT-induced PAH rats, pulmonary arterial and right ventricular pressures, right ventricular transverse diameter, pulmonary artery to aortic artery diameter ratio, and arterial oxidative stress increased, while Tricuspid annular plane systolic excursion, cardiac output, D/M ratio, and NO content decreased. Importantly, progesterone reversed these effects, highlighting its protective role in PAH progression. Conclusion Progesterone maintains pulmonary endothelial function by preserving eNOS coupling under physiological conditions. In PAH, it promotes eNOS re-coupling and reduces pulmonary pressure, making it a promising therapeutic strategy.