The aims of the present experiments were to define a new experimental model of pulmonary hypertension induced by a post-capillary mechanism and to assess the haemodynamic effects of nitric oxide on post-capillary pulmonary hypertension.Cardiopulmonary variables of 28 male beagle dogs, anaesthetized with chloralose, 16 spontaneous breathing and 12 with assisted ventilation, were studied before and after sino-aortic denervation (SAD). The haemodynamic effects of inhaled nitric oxide (25 p.p.m., 10?min), Nω-nitro-L-arginine methyl ester (20?mg?kg?1, i.v.), urapidil (0.5?mg?kg?1, i.v.) and propranolol (300?μg?kg?1, i.v.) were studied after SAD.SAD induced an acute and transient pulmonary hypertension, more marked in spontaneous breathing dogs. This pulmonary hypertension involved a post-capillary mechanism, secondary to the left ventricular haemodynamic effects of the acute increase of left ventricular after-load induced by systemic hypertension. In fact, the increase of mean pulmonary arterial pressure after SAD and the decrease of this parameter after urapidil or propranolol were strongly correlated with the variations of pulmonary capillary wedge pressure. Furthermore, no significant change in pulmonary vascular resistances was found after SAD or administration of α or β-adrenoceptor antagonists.Inhaled nitric oxide did not reverse pulmonary hypertension induced by SAD. Nω-nitro-L-arginine methyl ester had no significant haemodynamic effect on pulmonary circulation.In conclusion, the lack of effect of inhaled nitric oxide and nitric oxide synthase inhibitor on pulmonary circulation parameters after SAD suggests that endothelium-derived nitric oxide is not involved in the mechanisms leading to post-capillary pulmonary hypertension.
The early intervention with endothelinA(ETA) receptor antagonists following coronary artery ligation has been shown to reduce the development of pulmonary hypertension, despite a lack of improvement in left ventricular function.The present study examined the contribution of pulmonary vascular remodelling and the progression of lung fibrosis in the development of pulmonary hypertension and the subsequent role of endothelin-1 in these processes in a rat model of myocardial infarction (MI).The administration of 60?mg?kg?1per day of the specific ETAreceptor antagonist LU135253 ((+)-(S)-2-(4,6-dimethoxy-pyrimidin-2-yloxy)-3-methoxy-3,3-diphenyl-propionic acid) 24?h following coronary artery ligation, failed to improve left ventricular contractile indices, but reduced the extent of pulmonary hypertension, as reflected by the significant decrease in right ventricular systolic pressure.The medial wall thickness of small pulmonary arteries (50–200?μm) was significantly increased 4 weeks following MI, albeit LU135253 treatment did not ameliorate this pattern of vascular remodelling.The steady-state mRNA levels of collagen, fibronectin, transforming growth factor-β1, and -β3were significantly increased in the lungs of MI rats. The treatment with LU135252 did not alter this pattern of gene expression.Thus, these data demonstrate pulmonary vascular remodelling and the increased expression of extracellular matrix proteins represent underlying mechanisms implicated in the development of pulmonary hypertension in the MI rat.Despite the amelioration of the pulmonary hypertensive state, ETAreceptor blockade was insufficient to reverse pulmonary vascular remodelling, or the development of lung fibrosis in the MI rat.
Hypoxic pulmonary hypertension in rats (10% O2, 4 weeks) is characterized by changes in pulmonary vascular structure and function. The effects of the angiotensin converting enzyme inhibitor perindopril (oral gavage, once daily for the 4 weeks of hypoxia) on these changes were examined.Perindopril (30?mg?kg?1?d?1) caused an 18% reduction in pulmonary artery pressure in hypoxic rats.Structural changes (remodelling) in hypoxic rats included increases in (i) critical closing pressure in isolated perfused lungs (remodelling of arteries <50?μm o.d.) and (ii) medial wall thickness of intralobar pulmonary arteries, assessed histologically (vessels 30–100 and 101–500?μm o.d.). Perindopril 10 and 30?mg?kg?1?d?1attenuated remodelling in vessels ?100?μm (lungs and histology), 30?mg?kg?1?d?1was effective in vessels 101–500?μm but neither dose prevented hypertrophy of main pulmonary artery. 3?mg?kg?1?d?1was without effect.Perindopril (30?mg?kg?1?d?1) prevented the exaggerated hypoxic pulmonary vasoconstrictor response seen in perfused lungs from hypoxic rats but did not prevent any of the functional changes (i.e. the increased contractions to 5-HT, U46619 (thromboxane-mimetic) and K+and diminished contractions to angiotensins I and II) seen in isolated intralobar or main pulmonary arteries. Acetylcholine responses were unaltered in hypoxic rats.We conclude that, in hypoxic rats, altered pulmonary vascular function is largely independent of remodelling. Hence any drug that affects only remodelling is unlikely to restore pulmonary vascular function to normal and, like perindopril, may have only a modest effect on pulmonary artery pressure.
Responses to human urotensin-II (hU-II) were investigated in human and rat pulmonary arteries. Rat pulmonary arteries: hU-II was a potent vasoconstrictor of main pulmonary arteries (2–3?mm i.d.) (pEC50, 8.55±0.08,n=21) and was ～4 fold more potent than endothelin-1 ET-1] (P<0.01), although its Emaxwas considerably less (～2.5 fold,P<0.001). The potency of hU-II increased 2.5 fold with endothelium removal (P<0.05) and after raising vascular tone with ET-1 (P<0.01). Emaxwas enhanced ～1.5 fold in the presence of Nω-nitro-L-arginine methylester (L-NAME, 100?μM,P<0.01) and ～2 fold in vessels from pulmonary hypertensive rats exposed to 2 weeks chronic hypoxia (P<0.05). hU-II did not constrict smaller pulmonary arteries. Human pulmonary arteries (～250?μm i.d.): in the presence ofL-NAME, 3 out of 10 vessels contracted to hU-II and this contraction was highly variable. hU-II is, therefore, a potent vasoconstrictor of rat main pulmonary arteries and this response is increased by endothelial factors, vascular tone and onset of pulmonary hypertension. Inhibition of nitric oxide synthase uncovers contractile responses to hU-II in human pulmonary arteries.
1 The effects on pulmonary prostaglandin synthesis of pulmonary hypertension and oedema have been studied. 2 Seventeen isolated lungs of rabbit, cat and guinea-pig were perfused with plasma, whole blood or Krebs Ringer solution in a recirculating system. 3 The venous effluent from the lungs superfused (10 ml/min) a series of smooth muscle tissues sensitive to prostaglandins and thromboxane A2; these were: rat stomach strip, rat colon, chick rectum and rabbit aorta. 4 Left atrial pressure was increased by between 10 and 30 mmHg for periods of 3 to 59 minutes. Gross alveolar oedema eventually developed in all experiments. 5 Neither pulmonary hypertension nor subsequent oedema caused release of prostaglandins into the venous effluent.
Using anin vivomodel of pulmonary hypertension (PHT) secondary to left ventricular dysfunction (LVD), the pulmonary arterial response to the nitric oxide synthase (NOS) blockerL-NAME (30?μmol.min?1i.v.) and the subsequent responses to cumulatively administered endothelin-1 (ET-1) (0.001?–?4?nmol.kg?1i.v.) or big ET-1 (0.1?–?2.0?nmol.kg?1i.v.) were studied. Additionally, the effect of the non-selective ET-1 receptor antagonist, SB209670, was investigated.Eight weeks after coronary artery ligation or sham operation, rabbits demonstrated increased mean pulmonary arterial pressure (PAP) accompanied by right ventricular hypertrophy.Blockade of NOS caused a greater increase in basal PAP (increased by 7.7±1.1?mmHgc.f. 3.8±1.0?mmHg in controls,P<0.05) and uncovered a greater pulmonary pressor response to exogenous ET-1 in rabbits with PHT (increased by 10.2±2.3?mmHgc.f. 4.9±1.0?mmHg in controls,P<0.05).Big ET-1 evoked a pulmonary pressor effect, in both groups of rabbits, that was increased following blockade of NOS and was more potent in rabbits with PHT.The non-selective ET-1 receptor antagonist, SB209670, reduced basal PAP (from 16.9?mmHg to 15.9?mmHg,P<0.05) in rabbits with PHT and blocked the response to ET-1 in the presence ofL-NAME.In conclusion, the results demonstrate that basal NO activity masks a pulmonary pressor response to exogenously administered ET-1. An increased responsiveness to ET-1 was shown in the pulmonary arterial bed of rabbits with PHT secondary to LVD, implicating a pathophysiological role for ET-1 in this model.
Chronic hypoxic treatment of rats (to induce pulmonary hypertension, PHT) for 14 days increased cGMP-inhibited cAMP specific phosphodiesterase (PDE3) and cGMP binding cGMP specific phosphodiesterase (PDE5) activities in pulmonary arteries. The objective of this study was to establish the molecular basis for these changes in both animal and cell models of PHT. In this regard, RT–PCR and quantitative Western blotting analysis was applied to rat pulmonary artery homogenates and human pulmonary ‘artery' smooth muscle cell (HPASMC) lysates.PDE3A/B gene transcript levels were increased in the main, first, intrapulmonary and resistance pulmonary arteries by chronic hypoxia. mRNA transcript and protein levels of PDE5A2 in the main and first branch pulmonary arteries were also increased by chronic hypoxia, with no effect on PDE5A1/A2 in the intra-pulmonary and resistance vessels.The expression of PDE3A was increased in HPASMCs maintained under chronic hypoxic conditions for 14 days. This may be mediatedviaa protein kinase A-dependent mechanism, as treatment of cells with Br-cAMP (100 μM) mimicked chronic hypoxia in increasing PDE3A expression, while the PKA inhibitor, H8 peptide (50 μM) abolished the hypoxic-dependent increase in PDE3A transcript.We also found that the treatment of HPASMCs with the inhibitor of κB degradation Tosyl-Leucyl-Chloro-Ketone (TLCK, 50 μM) reduced PDE5 transcript levels, suggesting a role for this transcription factor in the regulation of PDE5 gene expression.Our results show that increased expression of PDE3 and PDE5 might explain some changes in vascular reactivity of pulmonary vessels from rats with PHT. We also report that NF-κB might regulate basal PDE5 expression.
The purpose of this study was to investigate whether a membrane-permeable superoxide dismutase mimetic, tempol, added either alone or in combination with the nitric oxide (NO) donor molsidomine, prevents the development of pulmonary hypertension (PH) in chronic hypoxic rats.Chronic hypobaric hypoxia (10% oxygen) for 2 weeks increased the right ventricular systolic pressure (RVSP), right ventricle and lung wet weight. Relaxations evoked by acetylcholine (ACh) and the molsidomine metabolite SIN-1 were impaired in isolated proximal, but not distal pulmonary arteries, from chronic hypoxic rats.Treatment with tempol (86 mg kg?1day?1in drinking water) normalized RVSP and reduced right ventricular hypertrophy, while systemic blood pressure, lung and liver weights, and blunted ACh relaxation of pulmonary arteries were unchanged.Treatment with molsidomine (15 mg kg?1day?1in drinking water) had the same effects as tempol, except that liver weight was reduced, and potassium and U46619-evoked vasoconstrictions in pulmonary arteries were increased. Combining tempol and molsidomine did not have additional effects compared to tempol alone. ACh relaxation in pulmonary arteries was not normalized by these treatments.The media to lumen diameter ratio of the pulmonary arteries was greater for the hypoxic rats compared to the normoxic rats, and was not reversed by treatment with tempol, molsidomine, or the combination of tempol and molsidomine.We conclude that tempol, like molsidomine, is able to correct RVSP and reduce right ventricular weight in the rat hypoxic model. Functional and structural properties of pulmonary small arteries were little affected. The results support the possibility that superoxide dismutase mimetics may be a useful means for the treatment of PH.