Impaired Pulmonary Arterial Vasoconstriction and Nitric Oxide–Mediated Relaxation Underlie Severe Pulmonary Hypertension in the Sugen-Hypoxia Rat Model

Abstract

Pulmonary vasoreactivity could determine the responsiveness to vasodilators and, in turn, the prognosis of pulmonary hypertension (PH). We hypothesized that pulmonary vasoreactivity is impaired, and we examined the underlying mechanisms in the Sugen-hypoxia rat model of severe PH. Male Sprague-Dawley rats were injected with Sugen (20 mg/kg s.c.) and exposed to hypoxia (9% O) for 3 weeks, followed by 4 weeks in normoxia (Su/Hx), or treated with Sugen alone (Su) or hypoxia alone (Hx) or neither (Nx). After hemodynamic measurements, the heart was assessed for right ventricular hypertrophy (Fulton's index); the pulmonary artery, aorta, and mesenteric arteries were isolated for vascular function studies; and contractile markers were measured in pulmonary arteries using quantitative polymerase chain reaction (PCR). Other rats were used for morphometric analysis of pulmonary vascular remodeling. Right ventricular systolic pressure and Fulton's index were higher in Su/Hx versus Su, Hx, and Nx rats. Pulmonary vascular remodeling was more prominent in Su/Hx versus Nx rats. In pulmonary artery rings, contraction to high KCl (96 mM) was less in Su/Hx versus Nx and Su, and phenylephrine-induced contraction was reduced in Su/Hx versus Nx, Hx, and Su. Acetylcholine (ACh)-induced relaxation was less in Su/Hx versus Nx and Hx, suggesting reduced endothelium-dependent vasodilation. ACh relaxation was inhibited by nitric oxide synthase (NOS) and guanylate cyclase blockade in all groups, suggesting a role of the NO-cGMP pathway. Nitrate/nitrite production in response to ACh was less in Su/Hx versus Nx, supporting reduced endothelial NO production. Sodium nitroprusside (10 M) caused less relaxation in Su/Hx versus Nx, Hx, and Su, suggesting a decreased responsiveness of vascular smooth muscle (VSM) to vasodilators. Neither contraction nor relaxation differed in the aorta or mesenteric arteries of all groups. PCR analysis showed decreased expression of contractile markers in pulmonary artery of Su/Hx versus Nx. The reduced responsiveness to vasoconstrictors and NO-mediated vasodilation in the pulmonary, but not systemic, vessels may be an underlying mechanism of severe PH in Su/Hx rats and appears to involve attenuation of the NO relaxation pathway and a switch of pulmonary VSM cells to a synthetic less reactive phenotype.

Tsantan Sumtang Alleviates Chronic Hypoxia-Induced Pulmonary Hypertension by Inhibiting Proliferation of Pulmonary Vascular Cells

“…Based on the above results, the PGI2-cAMP pathway, NO-cGMP pathway, and the opening of K + channels (inward rectifier K + channels, large conductance Ca 2+ -activated K + channels, and voltage-dependent K + channels) seemed to be the main factors in Tsantan Sumtang-induced concentration-dependent pulmonary artery vasorelaxation. For monomer vascular dilators, acetylcholine shows weaker maximum vasorelaxation influence via the NO-cGMP pathway, but echinacoside is a very similar dilator at its highest concentration through the opening of NO-cGMP-PKG-BK Ca channels [37, 38]. According to these reports, both Tsantan Sumtang and monomers exhibited concentration-dependent vasorelaxation effects and reached their maximum rates at one specific dose, while as a compound medicine, the role of Tsantan Sumtang in vasorelaxation occurs through a combination of more pathways than that of monomers; however, further research is still needed [37, 38].…”

Adipokines and Metabolic Regulators in Human and Experimental Pulmonary Arterial Hypertension

“…Three commonly used and well described pulmonary hypertension (PH)-experimental models were utilized in this study (Schema- Figure S1 ): (i) Monocrotaline Model (MCT): A single subcutaneous injection of 60 mg/kg MCT (Sigma, St. Louis, MO, USA) was administered and rats were assessed for PH development 4 weeks after the injection. Control animals received the same volume of vehicle (normal saline), (ii) Sugen/Hypoxia rat model: Rats were administered a single subcutaneous injection of 20 mg/kg Sugen 5416 (Sigma, St. Louis, MO, USA) and were exposed to hypoxia at 9% O 2 in a chamber under the control of an Oxycycler controller (BioSpherix, Redfield, NY, USA) as previously described [ 66 , 67 , 68 ]. After three weeks of exposure to hypoxia, animals were returned to normoxia (room air at 21% O 2 ) for three days and then sacrificed.…”

Endogenous and Inhaled Nitric Oxide for the Treatment of Pulmonary Hypertension

“…Another adult rat model of severe PAH with precapillary obliterative lesion (SU/Hx model) shows similarities in the pulmonary vascular pathology to that of PAH in adults. This SU/Hx model, induced by combined SUGEN5416 (a vascular endothelial growth factor receptor II antagonist) and exposure to chronic hypoxia, showed a reduction of ACh-induced NO production and/or release in pulmonary arteries [15]. Another recent study has reported decreased CAV1 expression in the same model [16].…”

“…An inhalation study of 15 NO in rats investigated the metabolism of iNO. In the carcasses, 1.6% of total inhaled 15 N was detected, similar to the level of natural 15 N. This result suggests that iNO largely does not remain in the body.…”