The soluble guanylate cyclase stimulator, 1-nitro-2-phenylethane, reverses monocrotaline-induced pulmonary arterial hypertension in rats.

AIMS: We examined the effects of treatment with 1-nitro-2-phenylethane (NP), a novel soluble guanylate cyclase stimulator, on monocrotaline (MCT)-induced PAH in rats. MAIN METHODS: At day 0, male adult rats were injected with a single subcutaneous (s.c.) dose of monocrotaline (60 mg/kg). Control (CNT) rats received an equal volume of monocrotaline's vehicle only (s.c.). Four weeks later, MCT-treated rats were treated orally for 14 days with NP (50 mg/kg/day) (MCT-NP group) or its vehicle (Tween 2%) (MCT-V group). At the end of the treatment period and before invasive hemodynamic study, rats of all experimental groups were examined by echocardiography. KEY FINDINGS: With respect to CNT rats, MCT-V rats showed significant; (1) increases in pulmonary artery (PA) diameter, RV free wall thickness and end-diastolic RV area, and increase of Fulton index; (2) decreases in maximum pulmonary flow velocity, PA acceleration time (PAAT), PAAT/time of ejection ratio, and velocity-time integral; (3) increases in estimated mean pulmonary arterial pressure; (4) reduction of maximal relaxation to acetylcholine in aortic rings, and (5) increases in wall thickness of pulmonary arterioles. All these measured parameters were significantly reduced or even abolished by oral treatment with NP. SIGNIFICANCE: NP reversed endothelial dysfunction and pulmonary vascular remodeling, which in turn reduced ventricular hypertrophy. NP reduced pulmonary artery stiffness, normalized the pulmonary artery diameter and alleviated RV enlargement. Thus, NP may represent a new therapeutic or a complementary approach to treatment of PAH.

Soluble guanylate cyclase stimulator, trans-4-methoxy-ß-nitrostyrene, has a beneficial effect in monocrotaline-induced pulmonary arterial hypertension in rats.

The soluble guanylate cyclase (sGC)/GMPc pathway plays an important role in controlling pulmonary arterial hypertension (PAH). We investigated whether the novel sGC stimulator trans-4-methoxy-ß-nitrostyrene (T4MN), ameliorates monocrotaline (MCT)-induced PAH. At Day 0, rats were injected with MCT (60 mg/kg, s. c.). Control (CNT) rats received an equal volume of monocrotaline vehicle only (s.c.). Four weeks later, MCT-treated rats were orally treated for 14 days with T4MN (75 mg/kg/day) (MCT-T4MN group) or its vehicle (MCT-V group), and with sildenafil (SIL; 50 mg/kg) (MCT-SIL group). Compared to the CNT group, MCT treatment induced a significant increase in both the Fulton index and RV systolic pressure but significantly reduced the maximum relaxation induced by acetylcholine. Indeed, MCT treatment increased the wall thickness of small and larger pulmonary arterioles. Oral treatment with T4MN and SIL reduced the Fulton index and RV systolic pressure compared to the MCT-V group. Maximum relaxation induced by acetylcholine was significantly enhanced in MCT-SIL group. Both T4MN and SIL significantly reduced the enhanced wall thickness of small and larger pulmonary arterioles. Treatment with T4MN has a beneficial effect on PAH by reducing RV systolic pressure and consequently right ventricular hypertrophy, and by reducing pulmonary artery remodeling. T4MN may represent a new therapeutic or complementary approach for the treatment of PAH.

Vasodilatory action of trans-4-methoxy-ß-nitrostyrene in rat isolated pulmonary artery.

Trans-4-methoxy-ß-nitrostyrene (T4MN) induced more potent vasorelaxant effects in resistance arteries from hypertensive rats than its parent drug, ß-nitrostyrene 1-nitro-2-phenylethene (NPe). To better understand the influence of insertion of the electron-releasing methoxy group in the aromatic ring of NPe, we investigated vasorelaxant effects of T4MN in isolated pulmonary artery and compared them with those of NPe in view of the potential interest of T4MN in pulmonary arterial hypertension. T4MN and NPe both caused concentration-dependent vasorelaxation in pulmonary artery rings pre-contracted with either phenylephrine (1 µmol/L) or KCl (60 mmol/L), an effect unaffected by endothelium removal. In endothelium-intact preparations pre-contracted with phenylephrine, the vasorelaxant effect of T4MN was more potent than that of NPe. However, unlike NPe, this effect was significantly reduced following pretreatment with 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) (10 µmol/L, a guanylate cyclase inhibitor) or tetraethylammonium (5 mmol/L, a potassium channel blocker). T4MN abolished the CaCl2 -induced contractions in pulmonary artery preparations stimulated with phenylephrine (PHE) under Ca2+ -free conditions in the presence of verapamil, to preferentially activate receptor-operated calcium channels. From these findings, we propose that T4MN evokes endothelium-independent vasorelaxant effects in isolated rat pulmonary artery, partially by inhibiting Ca2+ influx through L-type Ca2+ channels, as well as by activating soluble guanylate cyclase and potassium channels. The present results suggest the therapeutic potential of T4MN in treating pulmonary arterial hypertension.

Vasorelaxant effect of trans-4-chloro-ß-nitrostyrene, a synthetic nitroderivative, in rat thoracic aorta.

Previously, we showed that 1-nitro-2-phenylethene, a nitrostyrene derivative of 1-nitro-2-phenylethane, induced vasorelaxant effects in rat aorta preparations. Here, we studied mechanisms underlying the vasorelaxant effects of its structural analog, trans-4-chloro-ß-nitrostyrene (T4CN), in rat aortic rings. Increasing concentrations of T4CN (0.54-544.69 µm) fully and similarly relaxed contractions induced by phenylephrine (PHE, 1 µm) or KCl (60 mm) in endothelium-intact aortic rings with IC50 values of 66.74 [59.66-89.04] and 79.41 [39.92-158.01] µm, respectively. In both electromechanical and pharmacomechanical couplings, the vasorelaxant effects of T4CN remained unaltered by endothelium removal, as evidenced by the IC50 values (108.35 [56.49-207.78] and 65.92 [39.72-109.40] µm, respectively). Pretreatment of endothelium-intact preparations with L-NAME, ODQ, glibenclamide, or TEA did not change the vasorelaxant effect of T4CN. Under Ca2+ -free conditions, T4CN significantly reduced the phasic contractions induced by caffeine or PHE, as well as the contractions due to exogenous CaCl2 in aortic preparations stimulated with PHE (in the presence of verapamil). These results suggest that in rat aortic rings, T4CN induced vasorelaxation independently from the activation of soluble guanylate cyclase/cGMP pathway, an effect that may be related to the electrophilicity of the substituted chloro-nitrostyrene. This vasorelaxation seems to involve inhibition of both calcium influx from the extracellular milieu and calcium mobilization from intracellular stores mediated by IP3 receptors and by ryanodine-sensitive Ca2+ channels.

Vasorelaxation induced by methyl cinnamate, the major constituent of the essential oil of Ocimum micranthum, in rat isolated aorta.

The aim of the present study was to investigate the vascular effects of the E-isomer of methyl cinnamate (E-MC) in rat isolated aortic rings and the putative mechanisms underlying these effects. At 1-3000 µmol/L, E-MC concentration-dependently relaxed endothelium-intact aortic preparations that had been precontracted with phenylephrine (PHE; 1 µmol/L), with an IC50 value (geometric mean) of 877.6 µmol/L (95% confidence interval (CI) 784.1-982.2 µmol/L). These vasorelaxant effects of E-MC remained unchanged after removal of the vascular endothelium (IC50 725.5 µmol/L; 95% CI 546.4-963.6 µmol/L) and pretreatment with 100 µmol/L N(G) -nitro-l-arginine methyl ester (IC50 749.0 µmol/L; 95% CI 557.8-1005.7 µmol/L) or 10 µmol/L 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (IC50 837.2 µmol/L; 95% CI 511.4-1370.5 µmol/L). Over the concentration range 1-3000 µmol/L, E-MC relaxed K(+) -induced contractions in mesenteric artery preparations (IC50 314.5 µmol/L; 95% CI 141.9-697.0 µmol/L) with greater potency than in aortic preparations (IC50 1144.7 µmol/L; 95% CI 823.2-1591.9 µmol/L). In the presence of a saturating contractile concentration of K(+) (150 mmol/L) in Ca(2+) -containing medium combined with 3 µmol/L PHE, 1000 µmol/L E-MC only partially reversed the contractile response. In contrast, under similar conditions, E-MC nearly fully relaxed PHE-induced contractions in aortic rings in a Ba(2+) -containing medium. In preparations that were maintained under Ca(2+) -free conditions, 600 and 1000 µmol/L E-MC significantly reduced the contractions induced by exogenous Ca(2+) or Ba(2+) in KCl-precontracted preparations, but not in PHE-precontracted preparations (in the presence of 1 µmol/L verapamil). In addition, E-MC (1-3000 µmol/L) concentration-dependently relaxed the contractions induced by 2 mmol/L sodium orthovanadate. Based on these observations, E-MC-induced endothelium-independent vasorelaxant effects appear to be preferentially mediated by inhibition of plasmalemmal Ca(2+) influx through voltage-dependent Ca(2+) channels. However, the involvement of a myogenic mechanism in the effects of E-MC is also possible.