ROLE OF INHIBITION OF NITRIC-OXIDE PRODUCTION IN MONOCROTALINE-INDUCED PULMONARY-HYPERTENSION

Monocrotaline (MCT)induced pulmonary hypertension (PH) is associated w ith impaired endothelium-dependent nitric oxide (NO)-mediated relaxati on. To examine the role of NO in PH, Sprague-Dawley rats were given a single subcutaneous injection of normal saline [control (C)], 80 mg/kg MCT, or the same dose of MCT and a continuous subcutaneous infusion o f 2 mg.kg-(1).day(-1) of molsidomine, a NO prodrug (MCT+MD). Two weeks later, plasma NO3- levels, pulmonary arterial pressure (Ppa), ratio o f right-to-left ventricular weights (RV/LV) to assess right ventricula r hypertrophy, and pulmonary histology were evaluated. The plasma NO, level in the MCT group was reduced to 9.2 +/- 1.5 mu M (n = 12) vs. C level of 17.7 +/- 1.8 mu M (n = 8; P 0.02). In the MCT+MD group, plasm a NO3- level was 12.3 +/- 2.0 mu M (n = 8). Ppa and RV/LV in the MCT g roup were increased compared with C [Ppa, 34 +/- 3.4 mmHg (n = 6) vs. 19 +/- 0.8 mmHg (n = 8) and 0.41 +/- 0.01 (n = 9) vs. 0.25 +/- 0.008 ( 12 = 8), respectively; P < 0.001]. In the MCT+MD group, Ppa and RV/LV were not different when compared with C [19 +/- 0.5 mmHg (n = 5) and 0 .27 +/- 0.01 (n = 9), respectively; P < 0.001 vs. MCT]. Medial wall th ickness of lung vessels in the MCT group was increased compared with C [31 +/- 1.5% (n = 9) vs. 13 +/- 0.66% (n = 9); P < 0.001], and MD par tially prevented MCT-induced pulmonary vascular remodeling [22 +/- 1.2 % (n = 11); P < 0.001 vs. MCT and C]. These results indicate that a de fect in the availability of bioactive NO may play an important role in the pathogenesis of MCT-induced PH.