Rho kinase and Ca²⁺ entry mediate increased pulmonary and systemic vascular resistance in l-NAME-treated rats

Abstract

The small GTP-binding protein and its downstream effector Rho kinase play an important role in the regulation of vasoconstrictor tone. Rho kinase activation maintains increased pulmonary vascular tone and mediates the vasoconstrictor response to nitric oxide (NO) synthesis inhibition in chronically hypoxic rats and in the ovine fetal lung. However, the role of Rho kinase in mediating pulmonary vasoconstriction after NO synthesis inhibition has not been examined in the intact rat. To address this question, cardiovascular responses to the Rho kinase inhibitor fasudil were studied at baseline and after administration of an NO synthesis inhibitor. In the intact rat, intravenous injections of fasudil cause dose-dependent decreases in systemic arterial pressure, small decreases in pulmonary arterial pressure, and increases in cardiac output. L-NAME caused a significant increase in pulmonary and systemic arterial pressures and a decrease in cardiac output. The intravenous injections of fasudil after L-NAME caused dose-dependent decreases in pulmonary and systemic arterial pressure and increases in cardiac output, and the percent decreases in pulmonary arterial pressure in response to the lower doses of fasudil were greater than decreases in systemic arterial pressure. The Ca(++) entry blocker isradipine also decreased pulmonary and systemic arterial pressure in L-NAME-treated rats. Infusion of sodium nitroprusside restored pulmonary arterial pressure to baseline values after administration of L-NAME. These data provide evidence in support of the hypothesis that increases in pulmonary and systemic vascular resistance following L-NAME treatment are mediated by Rho kinase and Ca(++) entry through L-type channels, and that responses to L-NAME can be reversed by an NO donor.

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

“…The intravenous injection of fasudil or isradipine reversed the pulmonary hypertensive response to hypoxia in L-NAME-treated animals. The dose of L-NAME used in this study is lower than doses used in our previous study and provides support for the hypothesis that constitutive release of NO from the endothelium plays an important role in the maintenance of low baseline tone and in modulating the pulmonary vasoconstrictor response to hypoxia in the intact rat and is consistent with results of previous studies (9,11). The observation that the response to hypoxia can be reversed by fasudil or isradipine in L-NAME-treated rats suggests that calcium entry and/or sensitization may be involved in the vasoconstrictor response and is consistent with previous data (27).…”

“…†Returned back to control value. induced pulmonary hypertension, less is known about responses to the Rho-kinase inhibitor under physiological conditions when tone is increased on an acute basis (1,2,9,10,12,15,16,27,29,30).…”

“…A femoral artery was catheterized with PE 50 tubing for the measurement of systemic arterial pressure, and the left jugular and femoral veins were catheterized with PE 50 tubing for intravenous injections or infusions of drugs and fluids. For measurement of pulmonary arterial pressure, a specially designed single lumen 3F catheter with a radio-opaque marker and curved tip was passed from the right jugular vein into the right ventricle and main pulmonary artery under fluoroscopic guidance (Picker Surveyor), as described previously (9,13). Pulmonary and systemic arterial pressures were measured with NAMIC Perceptor transducers (Boston Scientific), digitized by a BIOPAC MP100 data acquisition system, and stored on a Dell PC.…”

“…It has also been reported that chronic hypoxia induces Rhokinase-dependent myogenic tone in small pulmonary arteries from the rat (7). Although it has been reported that fasudil, a selective Rho-kinase inhibitor, decreases pulmonary arterial pressure when pulmonary vascular resistance is increased by chronic hypoxia, monocrotaline, or nitro-L-arginine methyl ester (L-NAME), less is known about the responses to the Rho-kinase inhibitor when pulmonary vascular resistance is increased on an acute basis by vasoconstrictor agents or hypoxia in a physiological setting (9,10,30). The present study was therefore undertaken to investigate responses to fasudil when pulmonary vascular resistance was increased with U-46619 and ventilation with a 10% O 2 -90% N 2 gas mixture.…”

Pulmonary vasodilator responses to sodium nitrite are mediated by an allopurinol-sensitive mechanism in the rat

“…The left jugular and femoral veins were catheterized with PE50 tubing for iv administration and infusion of drugs and fluids. For measurement of pulmonary arterial pressure, a 3F catheter with a radiopaque marker and curved tip was passed from the right jugular vein into the main pulmonary artery under fluoroscopic guidance (Picker C-arm fluoroscope), as described previously (9,18). Left ventricular end-diastolic pressure was measured in some experiments by placement of a 3F radiopaque catheter in the chamber under fluoroscopic guidance.…”