Comparison of vascular and respiratory effects of endothelin-1 in the pig

The haemodynamic and respiratory responses caused by i.v. administration of endothelin-1 (ET-1) (20-100 pmol/kg) were studied in anaesthetized spontaneously breathing pigs. Intravenous bolus administration of synthetic ET-1 (40-100 pmol/kg) caused a transient decrease followed by a long-lasting increase in mean pulmonary arterial pressure and dose dependent vasoconstriction both in the systemic and pulmonary circulations. The effect on pulmonary arterial pressure was biphasic, with an initial transient fall followed by a long-lasting dose dependent increase. A biphasic response of the systemic mean arterial pressure was demonstrated only at a high dose of ET-1 (100 pmol/kg). ET-1 administration did not significantly change breathing pattern or phasic vagal input, but caused a significant decrease in passive compliance. Passive resistances or active compliance and resistances of the respiratory system were not modified. These results suggest that in the pig ET-1 is a more potent constrictor of vascular than of bronchial smooth muscle. The vasoconstrictor activity was greater in the pulmonary than the systemic circulations.     

Selective pulmonary vasodilation with ATP-MgCl2 during pulmonary hypertension in lambs

We investigated the effects of infusions of ATP-MgCl2 on the circulation in 11 spontaneously breathing newborn lambs during pulmonary hypertension induced either by the infusion of U-46619, a thromboxane A2 mimetic, or by hypoxia. During pulmonary hypertension induced by U-46619, ATP-MgCl2 (0.01-1.0 mg.kg-1.min-1) caused a significant dose-dependent decrease in pulmonary arterial pressure (12.4-40.7%, P less than 0.05), while systemic arterial pressure decreased only at the highest doses (P less than 0.05). Left atrial infusions of ATP-MgCl2 caused systemic hypotension without decreasing pulmonary arterial pressure. During hypoxia-induced pulmonary hypertension, ATP-MgCl2 caused a similar significant dose-dependent decrease in pulmonary arterial pressure (12.0-41.1%, P less than 0.05), while systemic arterial pressure decreased only at high doses (P less than 0.05). Regression analysis showed selectivity of the vasodilating effects of ATP-MgCl2 for the pulmonary circulation during pulmonary hypertension induced either by U-46619 or hypoxia. ATP-MgCl2 is a potent vasodilator with a rapid metabolism that allows for selective vasodilation of the vascular bed first encountered (pulmonary or systemic). We conclude that infusions of ATP-MgCl2 may be clinically useful in the treatment of children with pulmonary hypertension.     

Rescue treatment with a Rho-kinase inhibitor normalizes right ventricular function and reverses remodeling in juvenile rats with chronic pulmonary hypertension

Chronic pulmonary hypertension in infancy and childhood is characterized by a fixed and progressive increase in pulmonary arterial pressure and resistance, pulmonary arterial remodeling, and right ventricular hypertrophy and systolic dysfunction. These abnormalities are replicated in neonatal rats chronically exposed to hypoxia from birth in which increased activity of Rho-kinase (ROCK) is critical to injury, as evidenced by preventive effects of ROCK inhibitors. Our objective in the present study was to examine the reversing effects of a late or rescue approach to treatment with a ROCK inhibitor on the pulmonary and cardiac manifestations of established chronic hypoxic pulmonary hypertension. Rat pups were exposed to air or hypoxia (13% O(2)) from postnatal day 1 and were treated with Y-27632 (15 mg/kg) or saline vehicle by twice daily subcutaneous injection commencing on day 14, for up to 7 days. Treatment with Y-27632 significantly attenuated right ventricular hypertrophy, reversed arterial wall remodeling, and completely normalized right ventricular systolic function in hypoxia-exposed animals. Reversal of arterial wall remodeling was accompanied by increased apoptosis and attenuated content of endothelin (ET)-1 and ET(A) receptors. Treatment of primary cultured juvenile rat pulmonary artery smooth muscle cells with Y-27632 attenuated serum-stimulated ROCK activity and proliferation and increased apoptosis. Smooth muscle apoptosis was also induced by short interfering RNA-mediated knockdown of ROCK-II, but not of ROCK-I. We conclude that sustained rescue treatment with a ROCK inhibitor reversed both the hemodynamic and structural abnormalities of chronic hypoxic pulmonary hypertension in juvenile rats and normalized right ventricular systolic function. Attenuated expression and activity of ET-1 and its A-type receptor on pulmonary arterial smooth muscle was a likely contributor to the stimulatory effects of ROCK inhibition on apoptosis. In addition, our data suggest that ROCK-II may be dominant in enhancing survival of pulmonary arterial smooth muscle.     

In vivo attenuation of endothelium-dependent pulmonary vasodilation by methylene blue.

In vitro evidence suggests that resting pulmonary vascular tone and endothelium-dependent pulmonary vasodilation are mediated by changes in vascular smooth muscle concentrations of guanosine 3',5'-cyclic monophosphate (cGMP). We investigated this hypothesis in vivo in 19 mechanically ventilated intact lambs by determining the hemodynamic effects of methylene blue (a guanylate cyclase inhibitor) and then by comparing the hemodynamic response to five vasodilators during pulmonary hypertension induced by the infusion of U-46619 (a thromboxane A2 mimic) or methylene blue. Methylene blue caused a significant time-dependent increase in pulmonary arterial pressure. During U-46619 infusions, acetylcholine, ATP-MgCl2, sodium nitroprusside, isoproterenol, and 8-bromo-cGMP decreased pulmonary arterial pressure. During methylene blue infusions, the decreases in pulmonary arterial pressure caused by acetylcholine and ATP-MgCl2 (endothelium-dependent vasodilators) and sodium nitroprusside (an endothelium-independent guanylate cyclase-dependent vasodilator) were attenuated by greater than 50%. The decreases in pulmonary arterial pressure caused by isoproterenol and 8-bromo-cGMP (endothelium-independent vasodilators) were unchanged. This study in intact lambs supports the in vitro evidence that changes in vascular smooth muscle cell concentrations of cGMP in part mediate resting pulmonary vascular tone and endothelium-dependent pulmonary vasodilation.     

Effect of aminophylline on transpulmonary passage of venous air emboli in pigs.

Aminophylline has been shown to dramatically reduce the filtering capacity of the lung in dogs during venous air embolism. Similarities have been pointed out between the cardiovascular and respiratory systems of the pig and of humans. We therefore wanted to find out whether aminophylline also modifies the transpulmonary spillover of microbubbles to the arterial circulation of the pig. Twenty-eight pigs were anesthetized with pentobarbital sodium and mechanically ventilated. Aminophylline was injected intravenously into 10 of the pigs before the introduction of air bubbles into the right ventricle, while the other 18 pigs served as controls. A transesophageal echocardiographic probe was used to detect eventual air bubbles in the left atrium or in the aorta. Pigs received either air infusion, at rates varying from 0.05 to 0.20 ml.kg-1.min-1, or calibrated microbubbles, 5-300 microns diam. We found that aminophylline-treated pigs did not show any change in spillover incidence compared with controls. Furthermore, in both groups the spillover during continuous air infusion seemed to be a preterminal event, because the pigs had very low arterial pressure when arterial bubbles were observed. Finally, there was an increase in mean pulmonary arterial pressure from 18 +/- 3.4 to 26 +/- 2.2 (SD) mmHg (n = 4, P less than 0.01) in aminophylline-treated pigs after a bolus injection of microbubbles (less than or equal to 50 microns, total volume less than 0.5 ml). Our results suggest that aminophylline does not modify the transpulmonary passage of microbubbles in this porcine model. In addition, it would seem that the pulmonary circulation of the pig is sensitive to very small volumes of air, when injected as microbubbles.     

Altered pulmonary vasoreactivity in the chronically hypoxic lung

Prolonged exposure to alveolar hypoxia induces physiological changes in the pulmonary vasculature that result in the development of pulmonary hypertension. A hallmark of hypoxic pulmonary hypertension is an increase in vasomotor tone. In vivo, pulmonary arterial smooth muscle cell contraction is influenced by vasoconstrictor and vasodilator factors secreted from the endothelium, lung parenchyma and in the circulation. During chronic hypoxia, production of vasoconstrictors such as endothelin-1 and angiotensin II is enhanced locally in the lung, while synthesis of vasodilators may be reduced. Altered reactivity to these vasoactive agonists is another physiological consequence of chronic exposure to hypoxia. Enhanced contraction in response to endothelin-1 and angiotensin II, as well as depressed vasodilation in response to endothelium-derived vasodilators, has been documented in models of hypoxic pulmonary hypertension. Chronic hypoxia may also have direct effects on pulmonary vascular smooth muscle cells, modulating receptor population, ion channel activity or signal transduction pathways. Following prolonged hypoxic exposure, pulmonary vascular smooth muscle exhibits alterations in K+ current, membrane depolarization, elevation in resting cytosolic calcium and changes in signal transduction pathways. These changes in the electrophysiological parameters of pulmonary vascular smooth muscle cells are likely associated with an increase in basal tone. Thus, hypoxia-induced modifications in pulmonary arterial myocyte function, changes in synthesis of vasoactive factors and altered vasoresponsiveness to these agents may shift the environment in the lung to one of contraction instead of relaxation, resulting in increased pulmonary vascular resistance and elevated pulmonary arterial pressure.     

Intratracheal mesenchymal stem cell administration attenuates monocrotaline-induced pulmonary hypertension and endothelial dysfunction

The administration of mesenchymal stem cells (MSCs) has been proposed for the treatment of pulmonary hypertension. However, the effect of intratracheally administered MSCs on the pulmonary vascular bed in monocrotaline-treated rats has not been determined. In the present study, the effect of intratracheal administration of rat MSCs (rMSCs) on monocrotaline-induced pulmonary hypertension and impaired endothelium-dependent responses were investigated in the rat. Intravenous injection of monocrotaline increased pulmonary arterial pressure and vascular resistance and decreased pulmonary vascular responses to acetylcholine without altering responses to sodium nitroprusside and without altering systemic responses to the vasodilator agents when responses were evaluated at 5 wk. The intratracheal injection of 3 x 10(6) rMSCs 2 wk after administration of monocrotaline attenuated the rise in pulmonary arterial pressure and pulmonary vascular resistance and restored pulmonary responses to acetylcholine toward values measured in control rats. Treatment with rMSCs decreased the right ventricular hypertrophy induced by monocrotaline. Immunohistochemical studies showed widespread distribution of lacZ-labeled rMSCs in lung parenchyma surrounding airways in monocrotaline-treated rats. Immunofluorescence studies revealed that transplanted rMSCs retained expression of von Willebrand factor and smooth muscle actin markers specific for endothelial and smooth muscle phenotypes. However, immunolabeled cells were not detected in the wall of pulmonary vessels. These data suggest that the decrease in pulmonary vascular resistance and improvement in response to acetylcholine an endothelium-dependent vasodilator in monocrotaline-treated rats may result from a paracrine effect of the transplanted rMSCs in lung parenchyma, which improves vascular endothelial function in the monocrotaline-injured lung.     

Vasoconstrictor effect of endothelin-1 on hypertensive pulmonary arterial smooth muscle involves Rho-kinase and protein kinase C

Although one of the common characteristics of pulmonary hypertension is abnormal sustained vasoconstriction, the signaling pathways that mediate this heightened pulmonary vascular response are still not well defined. Protein kinase C (PKC) and Rho-kinase are regulators of smooth muscle contraction induced by G protein-coupled receptor agonists including endothelin-1 (ET-1), which has been implicated as a signaling pathway in pulmonary hypertension. Toward this end, it was hypothesized that both Rho-kinase and PKC mediate the pulmonary vascular response to ET-1 in hypertensive pulmonary arterial smooth muscle, and therefore, the purpose of this study was to determine the role of PKC and Rho-kinase signaling in ET-1-induced vasoconstriction in both normotensive (Sprague-Dawley) and hypertensive (Fawn-Hooded) rat pulmonary arterial smooth muscle. Results indicate that ET-1 caused greater vasoconstriction in hypertensive pulmonary arteries compared with the normal vessels, and treatment with the PKC antagonists chelerythrine, rottlerin, and G? 6983 inhibited the vasoconstrictor response to ET-1 in the hypertensive vessels. In addition, the specific Rho-kinase inhibitor Y-27632 significantly attenuated the effect of ET-1 in both normotensive and hypertensive phenotypes, with greater inhibition occurring in the hypertensive arteries. Furthermore, Western blot analysis revealed that ET-1 increased RhoA expression in both normotensive and hypertensive pulmonary arteries, with expression being greater in the hypertensive state. These results suggest that both PKC and Rho/Rho-kinase mediate the heightened pulmonary vascular response to ET-1 in hypertensive pulmonary arterial smooth muscle.     

Role of thromboxane A2 and platelet activating factor in early haemodynamic response to lipopolysaccharide in rats.

The mechanism of early pulmonary and systemic haemodynamic response to intravenous infusion of LPS from Escherichia coli was investigated in anesthetised Wistar rats. 10 mg of LPS given at a rate of 4 mg/kg/min but not at a rate of 1 mg/kg/min induced an increase in pulmonary arterial pressure (PAP) and a fall in systemic arterial pressure (SAP). Pretreatment with a PAF receptor antagonist; WEB 2170 (5 and 25 mg/kg) inhibited both PAP and SAP responses to LPS (4 mg/kg/min) while an inhibitor of thromboxane synthesis; Camonagrel (10 and 20 mg/kg) abolished PAP response without a major effect on SAP response to LPS. In conclusion, both PAF and TXA2 mediate LPS induced rise in pulmonary arterial pressure while LPS-induced fall in systemic arterial pressure is mediated by PAF.     

Hemodynamic effects of arginine vasopressin in rats adapted to chronic hypoxia

Acute and chronic pulmonary and systemic hemodynamic responses to arginine vasopressin (AVP) were examined in 4-wk hypoxia-adapted and air control rats. AVP, administered intravenously as bolus injections or sustained infusions, produced major dose-dependent V1-receptor-mediated reductions in mean pulmonary arterial pressure in hypoxia-adapted rats. These effects were comparable in pentobarbital-anesthetized, thoracotomized animals and in conscious, intact rats. Chronic infusions of AVP induced a sustained reduction in mean pulmonary arterial pressure and partially prevented the development of pulmonary hypertension without changing systemic arterial pressure. AVP induced significant decreases in cardiac output in both groups; the cardiac output response was not significantly different in hypoxia-adapted and air control animals. AVP induced almost no change in MPAP in air control rats. Furthermore the systemic pressor effects of AVP were significantly blunted in hypoxia-adapted rats compared with air controls. We conclude that the pulmonary depressor and blunted systemic pressor effects of AVP observed in hypoxia-adapted rats may be related to release of a vasodilator, such as endothelium-derived relaxing factor, vasodilator prostaglandins, or atrial natriuretic peptides. Further study is needed to elucidate these mechanisms and assess the usefulness of AVP and/or its analogues in the treatment and prevention of hypoxia-induced pulmonary hypertension.     

Adaptive response of pulmonary arterial smooth muscle to length change.

Hypervasoconstriction is associated with pulmonary hypertension and dysfunction of the pulmonary arterial smooth muscle (PASM) is implicated. However, relatively little is known about the mechanical properties of PASM. Recent advances in our understanding of plastic adaptation in smooth muscle may shed light on the disease mechanism. In this study, we determined whether PASM is capable of adapting to length changes (especially shortening) and regain its contractile force. We examined the time course of length adaptation in PASM in response to step changes in length and to length oscillations mimicking the periodic stretches due to pulsatile arterial pressure. Rings from sheep pulmonary artery were mounted on myograph and stimulated using electrical field stimulation (12-16 s, 20 V, 60 Hz). The length-force relationship was determined at L(ref) to 0.6 L(ref), where L(ref) was a reference length close to the in situ length of PASM. The response to length oscillations was determined at L(ref), after the muscle was subjected to length oscillation of various amplitudes for 200 s at 1.5 Hz. Release (or stretch) of resting PASM from L(ref) to 0.6 (and vice versa) was followed by a significant force recovery (73 and 63%, respectively), characteristic of length adaptation. All recoveries of force followed a monoexponential time course. Length oscillations with amplitudes ranging from 5 to 20% L(ref) caused no significant change in force generation in subsequent contractions. It is concluded that, like many smooth muscles, PASM possesses substantial capability to adapt to changes in length. Under pathological conditions, this could contribute to hypervasoconstriction in pulmonary hypertension.     

The Rho kinase inhibitor azaindole-1 has long-acting vasodilator activity in the pulmonary vascular bed of the intact chest rat

Responses to a selective azaindole-based Rho kinase (ROCK) inhibitor (azaindole-1) were investigated in the rat. Intravenous injections of azaindole-1 (10-300 μg/kg), produced small decreases in pulmonary arterial pressure and larger decreases in systemic arterial pressure without changing cardiac output. Responses to azaindole-1 were slow in onset and long in duration. When baseline pulmonary vascular tone was increased with U46619 or L-NAME, the decreases in pulmonary arterial pressure in response to the ROCK inhibitor were increased. The ROCK inhibitor attenuated the increase in pulmonary arterial pressure in response to ventilatory hypoxia. Azaindole-1 decreased pulmonary and systemic arterial pressures in rats with monocrotaline-induced pulmonary hypertension. These results show that azaindole-1 has significant vasodilator activity in the pulmonary and systemic vascular beds and that responses are larger, slower in onset, and longer in duration when compared with the prototypical agent fasudil. Azaindole-1 reversed hypoxic pulmonary vasoconstriction and decreased pulmonary and systemic arterial pressures in a similar manner in rats with monocrotaline-induced pulmonary hypertension. These data suggest that ROCK is involved in regulating baseline tone in the pulmonary and systemic vascular beds, and that ROCK inhibition will promote vasodilation when tone is increased by diverse stimuli including treatment with monocrotaline.     

The Flavonoid Quercetin Reverses Pulmonary Hypertension in Rats

Quercetin is a dietary flavonoid which exerts vasodilator, antiplatelet and antiproliferative effects and reduces blood pressure, oxidative status and end-organ damage in humans and animal models of systemic hypertension. We hypothesized that oral quercetin treatment might be protective in a rat model of pulmonary arterial hypertension. Three weeks after injection of monocrotaline, quercetin (10 mg/kg/d per os) or vehicle was administered for 10 days to adult Wistar rats. Quercetin significantly reduced mortality. In surviving animals, quercetin decreased pulmonary arterial pressure, right ventricular hypertrophy and muscularization of small pulmonary arteries. Classic biomarkers of pulmonary arterial hypertension such as the downregulated expression of lung BMPR2, Kv1.5, Kv2.1, upregulated survivin, endothelial dysfunction and hyperresponsiveness to 5-HT were unaffected by quercetin. Quercetin significantly restored the decrease in Kv currents, the upregulation of 5-HT_2A receptors and reduced the Akt and S6 phosphorylation. In vitro, quercetin induced pulmonary artery vasodilator effects, inhibited pulmonary artery smooth muscle cell proliferation and induced apoptosis. In conclusion, quercetin is partially protective in this rat model of PAH. It delayed mortality by lowering PAP, RVH and vascular remodeling. Quercetin exerted effective vasodilator effects in isolated PA, inhibited cell proliferation and induced apoptosis in PASMCs. These effects were associated with decreased 5-HT_2A receptor expression and Akt and S6 phosphorylation and partially restored Kv currents. Therefore, quercetin could be useful in the treatment of PAH.     

Improved pulmonary artery buffering function during phenylephrine-induced pulmonary hypertension

The goal of this study was to determine the in vivo pulmonary arterial buffering function (BF) during acute and moderate pulmonary hypertension achieved by phenylephrine-induced smooth muscle activation.Pulmonary pressure (Konigsberg P7) and diameter (sonomicrometry) were measured in nine anesthetized sheep. Transit pulmonary arterial hypertension was induced by mechanical occlusion of the pulmonary artery (HP) and by phenylephrine infusion (5 g/kg/min) (PHE). A viscoelastic Kelvin-Voigt model was used. By increasing the values of the viscous modulus, the pressure-diameter hysteresis area was reduced to a minimum in order to obtain the purely elastic pressure-diameter relationship. The elastic index (E) was calculated as the first derivative of the exponential model of the purely elastic pressure-diameter relationship at the mean pressure point.Systolic, diastolic, mean and pulse pressures were similar during HP and PHE, but significantly higher with regard to control steady state. In HP, E and arterial diameter (both its minimum and maximum values) increased significantly. In contrast, when pulmonary hypertension was induced by VSM activation, E was maintained concomitantly with pulmonary artery vasoconstriction.Pulmonary hypertension produced by occlusion of the pulmonary artery increases elasticity. Smooth muscle activation may offset the deleterious effect of pulmonary hypertension on arterial wall elasticity by reducing E and impeding arterial dilatation and collagen recruitment, maintaining BF during pulmonary hypertension.     

Attenuation of pulmonary arterial smooth muscle cell proliferation following hypoxic pulmonary hypertension by the Na+/H+ exchange inhibitor amiloride

Chronic hypoxia results in pulmonary hypertension. To investigate the role of Na+/H+ exchange in this process, we determined the effect of amiloride, a Na+/H+ exchange inhibitor, on hypoxic pulmonary hypertension and pulmonary arterial smooth muscle cell proliferation, both in vivo and in vitro. Sprague-Dawley rats were placed either in a hypobaric, hypoxic chamber (10.5% 02) or under normal 21% O2 atmosphere for 8 h each day for 3 weeks. Rats under hypoxic conditions received 1, 3, or 10 mg/kg/d amiloride or the vehicle alone. Hematologic indices, including red blood cells, hemoglobin, hematocrit and mean corpuscular hemoglobin increased in hypoxic rats, but these changes were prevented by treatment with amiloride. In the hypoxic rats, the right ventricular systolic pressure and right ventricular hypertension index (weight ratio of right ventricular to left and septum together) were increased by 88% and 129%, respectively. Arteriolar wall thickness and area in the hypoxia-treated animals increased 3- and 2-fold, respectively, over normoxic controls; the increase in each of these indices was attenuated by amiloride in a dose-dependent manner. In cultured pulmonary arterial smooth muscle cells, hypoxia greatly increased cellular proliferation, and this similarly showed a dose-dependent attenuation in the presence of amiloride. Amiloride did not affect blood pressure in vivo or cause cell damage in vitro. These data suggest that the Na+/H+ exchange inhibitor amiloride may represent an effective adjunctive therapy in pulmonary hypertension induced by chronic hypoxia.     

Repeated inhalation of adrenomedullin ameliorates pulmonary hypertension and survival in monocrotaline rats

Adrenomedullin (AM) is a potent vasodilator peptide. We investigated whether inhalation of aerosolized AM ameliorates monocrotaline (MCT)-induced pulmonary hypertension in rats. Male Wistar rats given MCT (MCT rats) were assigned to receive repeated inhalation of AM (n = 8) or 0.9% saline (n = 8). AM (5 mug/kg) or saline was inhaled as an aerosol using an ultrasonic nebulizer for 30 min four times a day. After 3 wk of inhalation therapy, mean pulmonary arterial pressure and total pulmonary resistance were markedly lower in rats treated with AM than in those given saline [mean pulmonary arterial pressure: 22 +/- 2 vs. 35 +/- 1 mmHg (-37%); total pulmonary resistance: 0.048 +/- 0.004 vs. 0.104 +/- 0.006 mmHg.ml(-1).min(-1).kg(-1) (-54%), both P < 0.01]. Neither systemic arterial pressure nor heart rate was altered. Inhalation of AM significantly attenuated the increase in medial wall thickness of peripheral pulmonary arteries in MCT rats. Kaplan-Meier survival curves demonstrated that MCT rats treated with aerosolized AM had a significantly higher survival rate than those given saline (70% vs. 10% 6-wk survival, log-rank test, P < 0.01). In conclusion, repeated inhalation of AM inhibited MCT-induced pulmonary hypertension without systemic hypotension and thereby improved survival in MCT rats.     

Intravenous injection of propylene glycol causes pulmonary hypertension in sheep

Propylene glycol (30%) is the carrier base for pentobarbital sodium in preparations often used in research laboratories. It has caused pulmonary hypertension in calves, and we found it caused pulmonary hypertension in sheep as well. To investigate the mechanism of pulmonary hypertension with propylene glycol, we injected an average loading dose of 30% propylene glycol (0.5 ml/kg) into adult sheep, which was followed by a rise in thromboxane levels (P less than 0.05) in systemic arterial plasma and lung lymph and by a dramatic increase in pulmonary arterial pressure (17 +/- 1 to 35 +/- 4 mmHg, P less than 0.05) and a fall in cardiac output (2.7 +/- 0.5 to 1 +/- 0.2 l/min). Indomethacin pretreatment blocked the rise in thromboxane in lung lymph and arterial plasma and substantially, although not entirely, blocked the rise in pulmonary arterial pressure. Pulmonary intravascular macrophages (PIMS), which are present in sheep and calves, can release thromboxane in response to a stimulus. To test whether PIMS might be the source of the thromboxane and pulmonary hypertension, we injected propylene glycol into guinea pigs and dogs, which are reported to have no PIMS, as well as into newborn lambs, which are not believed to develop many PIMS until the 2nd wk of life. In dogs and guinea pigs there was no response to propylene glycol. In lambs there was a rise in pulmonary vascular resistance but significantly less than in adult sheep; indomethacin blocked this response.(ABSTRACT TRUNCATED AT 250 WORDS)     

The preventive and therapeutic effects of AAV1-KLF4-shRNA in cigarette smoke-induced pulmonary hypertension

We found previously that KLF4 expression was up-regulated in cultured rat and human pulmonary artery smooth muscle cells (PASMCs) exposed to cigarette smoke (CS) extract and in pulmonary artery from rats with pulmonary hypertension induced by CS. Here, we aim to investigate whether CS-induced pulmonary hypertension (PH) is prevented and ameliorated by targeted pulmonary vascular gene knockdown of KLF4 via adeno-associated virus 1 (AAV1)-KLF4-shRNA in vivo in rat model. The preventive and therapeutic effects were observed according to the different time-point of AAV1-KLF4-shRNA intratracheal administration. We tested haemodynamic measurements of systemic and pulmonary circulations and observed the degree of pulmonary vascular remodelling. In the preventive experiment, KLF4 expression and some pulmonary circulation hemodynamic measurements such as right ventricular systolic pressure (RVSP), mean right ventricular pressure (mRVP), peak RV pressure rate of rise (dP/dt max) and right ventricle (RV) contractility index were increased significantly in the CS-induced PH model. While in the prevention group (AAV1-KLF4-shRNA group), RVSP, mRVP, dP/dt max and RV contractility index which are associated with systolic function of right ventricle decreased and the degree of pulmonary vascular remodelling relieved. In the therapeutic experiment, we observed a similar trend. Our findings emphasize the feasibility of sustained pulmonary vascular KLF4 gene knockdown using intratracheal delivery of AAV1 in an animal model of cigarette smoke-induced PH and determined gene transfer of KLF4-shRNA could prevent and ameliorate the progression of PH.     

Vasodilator actions of several N-nitroso compounds

Recent studies have shown that N-nitroso compounds can activate arterial guanylate cyclase and relax isolated arterial smooth muscle; however, the effects of these substances on the cardiovascular system in the anesthetized cat are unknown. The present study was undertaken to compare the effects of several nitrosoguanidines and a nitrosamine, N-nitrosodimethylamine, on arterial guanylate cyclase activity, isolated arterial smooth muscle tone, and systemic vascular resistance in the anesthetized cat. Intravenous injections and infusions of the nitrosoguanidines glyceryl trinitrate (GTN) and sodium nitroprusside (SNP) decreased systemic arterial pressure. During intravenous infusion of the nitrosoguanidines GTN and SNP, cardiac output was unchanged at the peak of the decrease in aortic pressure, indicating that the nitrosoguanidines GTN and SNP both reduced systemic vascular resistance. In addition, intraarterial injections of the nitrosoguanidines produced dose-dependent decreases in perfusion pressure in the feline mesenteric vascular bed perfused at constant flow. These substances were potent relaxants of isolated arterial smooth muscle and markedly activated arterial guanylate cyclase. In contrast, N-nitrosodimethylamine was devoid of vasodilator activity in vivo and exerted only minimal effects on isolated arterial smooth muscle tone or on arterial guanylate cyclase activity. The present data demonstrate a relationship between guanylate cyclase activation and arterial smooth muscle relaxation and suggest that the vasodilator effects on resistance vessels in vivo in response to selected N-nitroso compounds may involve such a mechanism. Although the significance of the presently reported cardiovascular responses to N-nitroso compounds is uncertain, N-nitroso compounds may represent a previously unrecognized class of substances which can be formed in the body and which possess marked vasodilator activity. It is possible that this vasodilator activity may involve the relaxation of vascular smooth muscle through activation of guanylate cyclase.