Although hypoxic pulmonary vasoconstriction (HPV) has been recognized by many researchers, the precise mechanism remains unknown. As isolated pulmonary arteries will constrict in vitro in the response to hypoxia, the oxygen sensor/transduction mechanism must reside in the pulmonary arterial smooth muscle or in the endothelium, or in both. Unfortunately, much of the current evidence is conflicting, especially as to the dependency of HPV on the endothelium and the role of a K+ channel. Therefore, this experiment was attempted to clarify the dependency of HPV on the endothelium and the role of a K+ channel on HPV in rat pulmonary artery. The effects of hypoxia were investigated in isolated main pulmonary arteries precontracted with norepinephrine. Vascular rings were suspended for isometric tension recording in an organ chamber filled with a Krebs-Henseleit solution. Hypoxia was induced by gassing the chamber with 95% N2 + 5% CO2 and this was maintained for 20 min. Hypoxia elicited a vasoconstriction in arteries with endothelium. Mechanical disruption of the endothelium abolished HPV. There was no difference between the amplitude of the HPV induced by two consecutive hypoxic challenges and the effect of normoxic and hyperoxic control Krebs-Henseleit solution on a subsequent response to hypoxia. Inhibition of NO synthesis by treatment with N(omega)-nitro-L-arginine reduced HPV, but inhibition of a cyclooxygenase pathway by treatment with indomethacin had no effect on HPV. Blockades of a tetraetylammonium chloride-sensitive K+ channel abolished HPV. Verapamil, a Ca2+ entry blocker reduced HPV. In conclusion, these results suggest that HPV was dependent on the endothelium and that HPV can be considered to be induced by inhibition of the mechanisms of NO-dependent vasodilation such as the opening of a K+ channels.
Animal ; Anoxia/physiopathology* ; Blood Vessels/physiopathology ; Calcium Channel Blockers/pharmacology ; Cyclooxygenase Inhibitors/pharmacology ; Enzyme Inhibitors/pharmacology ; Indomethacin/pharmacology ; Nitroarginine/pharmacology ; Pulmonary Circulation/physiology* ; Pulmonary Circulation/drug effects ; Rats ; Tetraethylammonium/pharmacology ; Vasoconstriction/physiology* ; Vasoconstriction/drug effects ; Verapamil/pharmacology

BACKGROUNDThe RhoA/Rho kinase pathway may participate in the pathogenesis of hypoxia and monocrotaline induced pulmonary hypertension. This study tested whether RhoA/Rho kinase pathway is involved in the pathogenesis of high flow induced pulmonary hypertension in rats.

METHODSMale Wistar rats (4 weeks) were randomly divided into 4 shunt groups, 4 treated groups and 4 control groups. Shunt and treated groups underwent left common carotid artery/external jugular vein shunt operation. Control groups underwent sham operation. Treated groups received fasudil treatment and the others received same dose of saline. At weeks 1, 2, 4 and 8 of the study, right ventricular systolic pressure was measured and blood gases were analysed to calculate Qp/Qs. The weight ratio of right ventricle to left ventricle plus septum and the mean percentage of medial wall thickness in moderate sized pulmonary arteries were obtained. RhoA activity in pulmonary arteries was detected using Rho activity assay reagent. Rho kinase activity was quantified by the extent of MYPT1 phosphorylation with Western blot. Proliferating cells were evaluated using proliferating cell nuclear antigen immunohistological staining.

RESULTSCarotid artery/jugular vein shunt resulted in high pulmonary blood flow, both an acute and a chronic elevation of right ventricular systolic pressure, significant medial wall thickening characterized by smooth muscle cells proliferation, right ventricular hypertrophy and increased activation of RhoA and Rho kinase. Fasudil treatment lowered pulmonary artery systolic pressure, suppressed pulmonary artery smooth muscle cells proliferation, attenuated pulmonary artery medial wall thickening and inhibited right ventricular hypertrophy together with significant suppression of Rho kinase activity but not Rho activity.

CONCLUSIONSActivated RhoA/Rho kinase pathway is associated with both the acute pulmonary vasoconstriction and the chronic pulmonary artery remodelling of high flow induced pulmonary hypertension. Fasudil treatment could improve pulmonary hypertension by inhibiting Rho kinase activity.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine ; analogs & derivatives ; therapeutic use ; Animals ; Cell Proliferation ; drug effects ; Enzyme Activation ; drug effects ; Hypertension, Pulmonary ; drug therapy ; etiology ; Hypertrophy, Right Ventricular ; prevention & control ; Intracellular Signaling Peptides and Proteins ; antagonists & inhibitors ; physiology ; Male ; Muscle, Smooth, Vascular ; drug effects ; Protein Kinase Inhibitors ; therapeutic use ; Protein-Serine-Threonine Kinases ; antagonists & inhibitors ; physiology ; Pulmonary Artery ; pathology ; Pulmonary Circulation ; drug effects ; Rats ; Rats, Wistar ; Systole ; drug effects ; Vasoconstriction ; drug effects ; rho-Associated Kinases ; rhoA GTP-Binding Protein ; physiology

BACKGROUND: Endogenous nitric oxide (NO) induces the peripheral vasodilation via the activation of guanylate cyclase in patients with septic shock. The purpose of this study was to assess the acute effects of methylene blue (MB), which is an inhibitor of guanylate cyclase, on the hemodynamics and on the production of pro-inflammatory cytokines and nitric oxide (NO) in patients with refractory septic shock. METHODS: Twenty consecutive patients with refractory septic shock, which was defined as shock refractory to a dopamine infusion of more than 20 microgram/kg/min with the appropriate use of antibiotics and adequate volume replacement, received MB infusion of 1 mg/kg intravenously. The hemodynamic and respiratory variables were measured at baseline, 30, 60 and 120 min after an infusion of MB (1 mg/kg). The blood levels of NO, IL-1, IL-10 and TNF-alpha were measured at baseline, 30 and 120 min after MB infusion. RESULTS: The administration of MB induced an increase in the systemic vascular resistance (SVR) that resulted in an increase of the mean arterial pressure (MAP) in patients with refractory septic shock, and this was without a decrease in cardiac output. The administered MB induced an increase in pulmonary vascular resistance (PVR) that resulted in an increase of pulmonary arterial pressure (PAP), without any deterioration of gas exchange. However, the increases in SVR and PVR were not associated with the alteration of endogenous production of NO, IL-1, IL-10 and TNF-alpha. CONCLUSION: MB transiently elevated the MAP by increasing the SVR without altering the endogenous productions of NO, IL-1, IL-10 and TNF-alpha during the study period in patients with refractory septic shock.
Anti-Infective Agents, Urinary/administration & dosage/*therapeutic use ; Blood Pressure/*drug effects/physiology ; Comparative Study ; Cytokines/*blood ; Enzyme-Linked Immunosorbent Assay ; Female ; Humans ; Infusions, Intravenous ; Male ; Methylene Blue/administration & dosage/*therapeutic use ; Middle Aged ; Pulmonary Circulation/drug effects/physiology ; Research Support, Non-U.S. Gov't ; Retrospective Studies ; Shock, Septic/blood/*drug therapy/physiopathology ; Treatment Outcome ; Vascular Resistance/*drug effects/physiology