Downregulation of Soluble Guanylate Cyclase and Protein Kinase G in the Pulmonary Artery Leads to the Sensitization to Thromboxane A2 in the Monocrotaline‐induced Pulmonary Hypertensive Rats

Abstract

Thromboxane A2(TXA2) relates to physiological and pathophysiological conditions of pulmonary artery (PA). Here, we examined the role of TXA2 receptor (TP)-mediated signaling in the pathophysiology of pulmonary arterial hypertension (PAH). The responsiveness to contractile agonist in PA could be determined by signals related to vasodilation such as nitric oxide (NO), soluble guanylate cyclase (sGC) and cGMP-dependent kinase (PKG) pathway. In this study, the TP receptor agonist (U46619)-induced contraction and modulatory role of NO/cGMP signaling were investigated in a monocrotaline-induced PAH rat model (PAH-MCT). PA from PAH-MCT exhibited higher sensitivity to U46619, that is decreased EC50. Lower expression of eNOS, sGC, and PKG were observed while higher expression of RhoA-dependent kinase 2 (ROCK2) was revealed by immunoblot analysis in the PA from PAH-MCT and control. The higher sensitivity to U46619 in PAH-MCT was ameliorated by 8-Br-cGMP, a membrane-permeable cGMP analogue, but not by NO donor, sodium nitroprusside (SNP 30 µM). In contrast, in the control PA, sGC inhibition by 1H- [1,2,4] oxadiazolo [4,3-a] quinoxalin-1-one (ODQ) 10 µM lowered the threshold of U46619-induced contraction. In the presence of ODQ, SNP treatment did not present its regulatory effect whereas the addition of 8-Br-cGMP lowered the sensitivity to U46619. The inhibition of ROCK by Y-27632 also lowered the sensitivity to U46619 in both control and PAH-MCT. The study suggests that the attenuation of NO/cGMP signaling and the upregulation of ROCK2 increase the sensitivity to TXA2 in the PAH animal, which might have pathophysiological implications in patients with PAH.