Analysis of pulmonary vasodilator responses to the Rho-kinase inhibitor fasudil in the anesthetized rat

Abstract

Badejo AM Jr, Dhaliwal JS, Casey DB, Gallen TB, Greco AJ, Kadowitz PJ. Analysis of pulmonary vasodilator responses to the Rho-kinase inhibitor fasudil in the anesthetized rat. Am J Physiol Lung Cell Mol Physiol 295: L828 -L836, 2008. First published August 8, 2008 doi:10.1152/ajplung.00042.2008.-The small GTP-binding protein Rho and its downstream effector, Rho-kinase, are important regulators of vasoconstrictor tone. Rho-kinase is upregulated in experimental models of pulmonary hypertension, and Rho-kinase inhibitors decrease pulmonary arterial pressure in rodents with monocrotaline and chronic hypoxia-induced pulmonary hypertension. However, less is known about responses to fasudil when pulmonary vascular resistance is elevated on an acute basis by vasoconstrictor agents and ventilatory hypoxia. In the present study, intravenous injections of fasudil reversed pulmonary hypertensive responses to intravenous infusion of the thromboxane receptor agonist, U-46619 and ventilation with a 10% O2 gas mixture and inhibited pulmonary vasoconstrictor responses to intravenous injections of angiotensin II, BAY K 8644, and U-46619 without prior exposure to agonists, which can upregulate Rho-kinase activity. The calcium channel blocker isradipine and fasudil had similar effects and in small doses had additive effects in blunting vasoconstrictor responses, suggesting parallel and series mechanisms in the lung. When pulmonary vascular resistance was increased with U-46619, fasudil produced similar decreases in pulmonary and systemic arterial pressure, whereas isradipine produced greater decreases in systemic arterial pressure. The hypoxic pressor response was enhanced by 5-10 mg/kg iv nitro-Larginine methyl ester (L-NAME), and fasudil or isradipine reversed the pulmonary hypertensive response to hypoxia in control and in L-NAME-treated animals, suggesting that the response is mediated by Rho-kinase and L-type Ca 2ϩ channels. These results suggest that Rho-kinase is constitutively active in regulating baseline tone and vasoconstrictor responses in the lung under physiological conditions and that Rho-kinase inhibition attenuates pulmonary vasoconstrictor responses to agents that act by different mechanisms without prior exposure to the agonist.Rho-kinase pathway; Ca 2ϩ sensitization; pulmonary vascular bed; U-46619; isradipine; hypoxia; nitro-L-arginine methyl ester THE SMALL GTP-binding protein Rho and its downstream effector Rho-kinase play an important role in the regulation of vascular smooth muscle tone (3,4,6,18,20,28,34,36). It has been hypothesized that the Rho-kinase system is constitutively active in regulating vasoconstrictor tone and that upregulation of this pathway occurs in a variety of cardiovascular diseases (8,19,21,22,32,33,35). Rho-kinase has been shown to be a potential therapeutic target in a number of cardiovascular diseases including pulmonary hypertension (1,2,10,12,15,16,26,27,29,38). It has been reported that Rho-kinase is upregulated in monocrotaline and chronic hypoxia-induced pulmonary hypertensio...

Enhancement of myofilament calcium sensitivity by acute hypoxia in rat distal pulmonary arteries

“…Exoenzyme C3 and toxin B, which prevent activation of Rho kinase by the monomeric GTPase RhoA, and the Rho kinase inhibitors Y-27632 and HA-1077 blocked hypoxiainduced decreases in MLCP activity and increases in Rho kinase activity and [P-MLC 20 ] (74,75). Consistent with these findings, Y-27632 or HA-1077 also inhibited phase 2 HPV in precontracted pulmonary arteries (53,74) and HPV in isolated and intact lungs (2,8,16,43,53 …”

“…For example, Y-27632 and/or HA-1077, another Rho kinase inhibitor, blocked hypoxia-induced MLC 20 phosphorylation in PASMC (74,75) and HPV in pulmonary arteries (53,74), isolated lungs (16,53,73), and intact animals (2,8,43); however, Y-27632 and HA-1077 blocked [Ca 2ϩ ] i responses to hypoxia, Ca 2ϩ release from sarcoplasmic reticulum, and Ca 2ϩ entry through store-and voltage-operated Ca 2ϩ channels in rat PASMC (73), indicating that the effects of these agents could be due to blockade of [Ca 2ϩ ] i responses, rather than Ca 2ϩ desensitization. In this case, inhibition of MLC 20 phosphorylation in hypoxic PASMC by exoenzyme C3 and toxin B (74), which block activation of Rho kinase by RhoA, could also be due to inhibition of [Ca 2ϩ ] i responses.…”

Effects of Rho-Kinase Inhibition on Pulmonary Hypertension, Lung Growth, and Structure in Neonatal Rats Chronically Exposed to Hypoxia

“…Therefore, it is not possible, taking the present pharmacological approach, to distinguish indirect consequences of ROCK inhibitor-induced vasodilatation from limiting effects on other ROCK-mediated pathways. Other mechanisms, not explored in this study, by which ROCK inhibitors may have limited vascular remodeling include attenuated vascular production of endothelin-1 (27), inhibited downstream signaling of G-protein-coupled receptor ligands (11,28), and augmented function of the NO/ cyclic GMP pathway (29).…”

Analysis of Pulmonary Vasodilator Responses to SB-772077-B [4-(7-((3-Amino-1-pyrrolidinyl)carbonyl)-1-ethyl-1H-imidazo(4,5-c)pyridin-2-yl)-1,2,5-oxadiazol-3-amine], a Novel Aminofurazan-Based Rho Kinase Inhibitor

“…The left jugular and femoral veins were catheterized with PE50 tubing for intravenous injections and infusions. For measurement of pulmonary arterial pressure, a 3F single lumen catheter with a curved tip and radio-opaque marker was passed form the right jugular vein into the pulmonary artery under fluoroscopic guidance (Picker-Surveyor Fluoroscope) as described previously (Dhaliwal et al, 2007;Badejo et al, 2008). In some experiments, a 3F catheter was passed into the left ventricle from the right carotid artery to measure left ventricular end-diastolic pressure as a measure of left atrial pressure.…”

“…Rho kinase activity is up-regulated in a number of cardiovascular diseases, including pulmonary hypertension, and Rho kinase inhibitors have a beneficial effect in the treatment of pulmonary hypertensive disorders (Uehata et al, 1997;Seko et al, 2003;Abe et al, 2004;Rikitake and Liao, 2005;Budzyn et al, 2006). In addition to the potential role of Rho kinase in pulmonary hypertension, it has been proposed recently that Rho kinase is involved in the regulation of baseline tone in the cardiovascular system and that ROCK inhibition can blunt vasoconstrictor responses independent of the method used to promote vasoconstriction (Dhaliwal et al, 2007;Badejo et al, 2008). The studies on the role of ROCK have been assisted by the development of selective Rho kinase inhibitors, and Y-27632 and fasudil are the prototypical agents that selectively target p1601 ROCK (Asano et al, 1987;Ishizaki et al, 1996;Leung et al, 1996;Uehata et al, 1997).…”