Effectiveness of a nonselective ET(A/B) and a selective ET(A) antagonist in rats with monocrotaline-induced pulmonary hypertension.

Background: Both nonselective ET(A/B) receptor and selective ET(A) receptor antagonists can reduce pulmonary hypertension (PH) and right ventricular hypertrophy (RVH) in various animal models. Depending on their net effects after blockade of endothelial and smooth muscle ET(B) receptors, nonselective ET(A/B) antagonists could be more or less effective than selective ET(A) antagonists.

Methods And Results: Two weeks after injection of saline or 60 mg/kg monocrotaline (MCT), rats received 50 mg x kg(-1) x d(-1) of a selective (LU135252) or nonselective (BSF420627) antagonist for 3 weeks. This resulted in 4 groups: control (n=15), MCT (n=60), MCT+ET(A) (n=39), and MCT+ET(A/B) (n=40). Five-week survival was 35% in the MCT group; this was increased to 56% in the MCT+ET(A) group (P:=0.10) and to 67% in the MCT+ET(A/B) group (P:=0.0015). Drug administration was stopped 48 hours before hemodynamic measurements to evaluate the chronic effects of therapy: PH in the MCT group (RV systolic pressure 87+/-1 mm Hg) was improved similarly in both MCT+ET(A) and MCT+ET(A/B) groups (72+/-3 and 70+/-3 mm Hg, respectively, P:<0.05). Severe RVH in the MCT group (RV/left ventricle+septum weight ratio 73+/-1%) was not affected by the selective antagonist (70+/-2%) but was reduced to 54+/-2% in the MCT+ET(A/B) group (P:<0.01). Pulmonary resistive properties, assessed from isolated lung pressure-flow relationships, were improved similarly in survivors from both treated groups.

Conclusions: Both the nonselective ET(A/B) antagonist BSF420627 and the selective ET(A) antagonist LU135252 are effective in this model of PH. Similar direct comparative studies in other models of PH and with various dosage regimens are warranted to define the optimal pharmacological approach of PH when ET receptor antagonists are used.