Maladaptive right ventricular (RV) hypertrophic responses lead to RV dysfunction and failure in patients with pulmonary arterial hypertension, but the mechanisms responsible for these changes are not well understood. The objective of this study was to evaluate the effect of treatment with bosentan on RV hypertrophy (RVH), fibrosis and expression of protein kinase C (PKC) isoforms in the RV of rats exposed to chronic hypoxia. Methods Adult Sprague Dawley rats were housed in normoxia or hypoxia (FiO2: 10%) and administered vehicle or 100mg/kg/day of bosentan. After 3 weeks, echocardiographic, hemodynamic assessment was performed. PKC, procollagen-1, and collagen expression was assessed using immunoblot or colorimetric assay. Results RV systolic pressure (RVSP) and RVH were higher in hypoxic compared to normoxic animals (RVSP: 72 ± 4 vs. 25 ± 2 mmHg, p<0.05; RVH: 1.2 ± 0.06 vs. 0.5 ± 0.03 mg/g body wt., p<0.05). Bosentan had no effect on RVSP or mass in normoxic animals, but did attenuate RVH in hypoxic animals (Hypoxic/vehicle: 1.2 ± 0.06; Hypoxic/bosentan: 1.0 ± 0.05 mg/g body wt., p<0.05). Hypoxia increased RV procollagen-I, and total collagen expression, effects that were attenuated by bosentan treatment. Hypoxia increased RV total and cytosolic PKC-δ protein expression, but had no effect on PKC-α or -ε isoforms. Administration of bosentan did not affect total PKC-δ protein expression. However, animals treated with bosentan had an increase in membranous PKC-δ when exposed to hypoxia. Conclusion Bosentan inhibits RVH and RV collagen expression in rats exposed to chronic hypoxia possibly via alteration of PKCδ activity.

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