Progesterone inhibits vascular remodeling and attenuates monocrotaline-induced pulmonary hypertension in estrogen-deficient rats.

(Full text is available at http://www.manu.edu.mk/prilozi). Pulmonary arterial hypertension (PH) is predominantly a disease of young females. Yet, little is known regarding the effects of female sex hormones in PH. Female rats develop less severe PH compared to male rats, and ovariectomy (OVX) exacerbates PH. Although OVX rats treated with estradiol develop less severe disease, the role of progesterone in OVX-induced exacerbation of disease has not been examined. Progesterone was shown to dilate pulmonary vessels and to inhibit proliferation of endothelial and vascular smooth muscle cells. Therefore, we hypothesized that progesterone may confer protective effects in experimental PH. A total of 30 female rats were ovariectomized and OVX rats were randomly administered either saline (OVX-Control group, n = 7), monocrotaline (60mg/kg i.p.; OVX-MCT group; n = 12), or MCT plus progesterone (30microg/kg/h via osmotic minipumps; OVX-MCT+P group; n = 11). After 32 days animals were instrumented for in situ (open chest) measurements of right ventricle (RV) peak systolic (RVSP) and end diastolic (RVEDP) pressures, and tissue samples were obtained for morphometric and histological analysis. Administration of MCT elevated RVSP (22.2 +/- 1.1 vs. 46.7 +/- 2.4 mmHg) and RVEDP (1.51 +/- 0.86 vs. 11.9+/-2.2 mmHg), increased RV/left ventricle + septum (RV/LV+S) ratio (0.256 +/- 0.010 vs. 0.582 +/- 0.033, OVX vs. OVX-MCT), and induced media hypertrophy of small size pulmonary arteries. In ovariectomized pulmonary hypertensive rats, treatment with progesterone attenuated the severity of disease (OVX-MCT+P group: RVSP = 36.6 +/- 2.3 mmHg; RV/LV+S = 0.468 +/- 0.025; RVEDP = 7.5 +/-1.5 mmHg), attenuated vascular remodeling (media % index: 28.2 +/- 1.1 vs. 34.2 +/- 1.3), and reduced mortality (9% vs. 25%; OVX-MCT+P vs. OVX-MCT). This study provides the first evidence that in estrogen-deficient rats, progesterone has protective effects in MCT-induced PH. Further evaluation of the role of progesterone and its interaction with estrogens in pulmonary hypertension is warranted. Key words: Pulmonary Hypertension, Progesterone, Estrogens, Vascular remodeling.