calcimycin and Hypertension--Pulmonary

In the lung, nitric oxide (NO) derives from several cellular sources, forming networks of paracrine communication. In pulmonary vessels, NO produced by endothelial cells is a powerful vasodilator. In the airways, NO originates from epithelial cells and from adventitial nerve endings to induce smooth muscle relaxation. Activated macrophages can also produce large quantities of NO during lung immunological reactions. In the normal pulmonary circulation, NO not only mediates vasodilation, but also opposes vasoconstriction, prevents platelet adhesion, controls growth of smooth muscle and influences the composition of the extracellular matrix. During exposure to chronic hypoxia, impaired endothelial NO production contributes to the increased vasomotor tone and vascular remodelling leading to sustained pulmonary hypertension. Exogenous NO gas delivered via the airspaces is a selective pulmonary vasodilator. Inhaled NO is now used as a therapy to treat various forms of pulmonary hypertension and to improve arterial oxygenation during lung injury.

Topics: Animals; Calcimycin; Endothelium, Vascular; Humans; Hypertension, Pulmonary; Hypoxia; Lung; Nitric Oxide; Nitric Oxide Synthase; Pulmonary Circulation; Vasodilation

Reduced NO levels due to the deficiency of tetrahydrobiopterin (BH(4)) contribute to impaired vasodilation in pulmonary hypertension. Due to the chemically unstable nature of BH(4), it was hypothesised that oxidatively stable analogues of BH(4) would be able to support NO synthesis to improve endothelial dysfunction in pulmonary hypertension. Two analogues of BH(4), namely 6-hydroxymethyl pterin (HMP) and 6-acetyl-7,7-dimethyl-7,8-dihydropterin (ADDP), were evaluated for vasodilator activity on precontracted rat pulmonary artery rings. ADDP was administered to pulmonary hypertensive rats, followed by measurement of pulmonary vascular resistance in perfused lungs and eNOS expression by immunohistochemistry. ADDP and HMP caused significant relaxation in vitro in rat pulmonary arteries depleted of BH(4) with a maximum relaxation at 0.3μM (both P<0.05). Vasodilator activity of ADDP and HMP was completely abolished following preincubation with the NO synthase inhibitor, L-NAME. ADDP and HMP did not alter relaxation induced by carbachol or spermine NONOate. BH(4) itself did not produce relaxation. In rats receiving ADDP 14.1mg/kg/day, pulmonary vasodilation induced by calcium ionophore A23187 was augmented and eNOS immunoreactivity was increased. In conclusion, ADDP and HMP are two analogues of BH(4), which can act as oxidatively stable alternatives to BH(4) in causing NO-mediated vasorelaxation. Chronic treatment with ADDP resulted in improvement of NO-mediated pulmonary artery dilation and enhanced expression of eNOS in the pulmonary vascular endothelium. Chemically stable analogues of BH(4) may be able to limit endothelial dysfunction in the pulmonary vasculature.

Topics: Animals; Biopterins; Calcimycin; Calcium; Endothelium, Vascular; Gene Expression Regulation, Enzymologic; Hypertension, Pulmonary; Hypoxia; In Vitro Techniques; Ionophores; Male; Nitric Oxide; Nitric Oxide Synthase Type III; Pterins; Pulmonary Artery; Rats; Rats, Sprague-Dawley; Vasodilation

Several cases of systemic arteriovenous fistula diagnosed in the human fetus have been associated with the postnatal development of persistent pulmonary hypertension. The aim of this study was to determine the effects of a prenatally created systemic arteriovenous fistula on the structure and reactivity of the pulmonary circulation in the fetal lamb. A fistula between the jugular vein and carotid artery was created in fetal lambs at 119-124 days of gestation. At delivery (134-139 days), left pulmonary artery (LPA) pressure was increased in the fistula group (n = 12) compared with controls (n = 11, P < 0.01). The pulmonary vascular resistance was significantly higher in the fistula group (P < 0.05), whereas mean LPA blood flow was not statistically different between the two groups. Morphometric analysis of the pulmonary vascular bed revealed an increase in the number of peripheral muscular arteries, together with an increase in pulmonary arterial medial thickness in the fistula group. There was no difference in the relative number or size of intraacinar arteries. In vitro organ bath studies on pulmonary arterial rings showed impaired endothelium-dependent relaxation in the fistula group compared with controls. However, endothelial nitric oxide synthase protein expression was similar in both groups, whereas endothelium-independent relaxation to sodium nitroprusside was greater in the fistula group compared with controls. A systemic arteriovenous fistula leads to both structural and functional alteration of the pulmonary vasculature, which might lead to the development of persistent pulmonary hypertension after birth.

Topics: Acetylcholine; Animals; Arteriovenous Fistula; Blotting, Western; Calcimycin; Female; Hypertension, Pulmonary; Ionophores; Isometric Contraction; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Pregnancy; Pulmonary Artery; Pulmonary Circulation; Respiratory Mucosa; Sheep; Vasodilation; Vasodilator Agents

Nitric oxide (NO) plays a major role in the modulation of perinatal pulmonary vascular tone. Congenital diaphragmatic hernia (CDH), a major cause of severe persistent pulmonary hypertension of the newborn (PPHN), is often refractory to inhaled NO. Alterations in NO/cyclic guanosine 3',5' monophosphate (cGMP)-mediated pulmonary vasodilatation may contribute to PPHN in CDH. We assessed NO/cGMP-mediated pulmonary vasorelaxation in vitro in 140-d gestational lamb fetuses with surgically created left CDH (term = 147 d) to age-matched controls. Relaxation of fourth generation intralobar pulmonary artery rings in response to the endothelium-dependent vasodilator, acetylcholine (ACh), and to the specific inhibitor of cGMP-phosphodiesterase (PDE), zaprinast, did not differ between the two groups. By contrast, relaxation in response to the calcium ionophore A23187 was impaired in CDH as compared with control animals. Relaxation in response to the NO donor sodium nitroprusside (SNP) (a direct activator of soluble guanylyl cyclase [sGC]) was also impaired in CDH animals as compared with controls. Repeating the challenge increased vasorelaxation in response to SNP in CDH as compared with control animals. Immunohistochemistry revealed the presence of endothelial NO-synthase in the endothelium of pulmonary arteries from both control and CDH animals. We conclude that endothelium-dependent vasodilatation in response to ACh and A23187 was differently affected in the fetal surgical CDH-lamb model. Furthermore, activity of sGC but not that of PDE was impaired in CDH animals. PPHN and decreased inhaled NO responsiveness in CDH may involve decreased sGC activity.

Topics: Acetylcholine; Animals; Animals, Newborn; Calcimycin; Cyclic GMP; Disease Models, Animal; Epithelium; Female; Fetus; Guanylate Cyclase; Hernia, Diaphragmatic; Hypertension, Pulmonary; Immunohistochemistry; Ionophores; Isometric Contraction; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Nitroprusside; Pulmonary Artery; Receptors, Cytoplasmic and Nuclear; Sheep; Soluble Guanylyl Cyclase; Vasodilation

Congenital heart disease associated with increased pulmonary blood flow produces pulmonary hypertension. To characterize vascular alterations in the nitric oxide (NO)-cGMP cascade induced by increased pulmonary blood flow and pulmonary hypertension, 10 fetal lambs underwent in utero placement of an aortopulmonary vascular graft (shunt). When the lambs were 4-6 wk of age, we assessed responses of pulmonary arteries (PAs) and pulmonary veins (PVs) isolated from lungs of control and shunted lambs. PVs from control and shunted lambs relaxed similarly to exogenous NO (S-nitrosyl-acetyl-penicillamine), to NO produced endogenously (zaprinast and A-23187), and to cGMP (atrial natriuretic peptide). In contrast, relaxations to A-23187 and zaprinast were blunted in PAs isolated from shunted lambs relative to controls. Inhibitors of NO synthase (NOS) and soluble guanylate cyclase constricted control but not shunt PAs, indicating reduced basal NOS activity in shunt PAs. Pretreatment of shunt PAs with the substrates L-arginine and sepiapterin, a precursor for tetrahydrobiopterin synthesis, did not augment A-23187 relaxations. However, pretreatment with superoxide dismutase and catalase significantly enhanced A-23187 relaxations in shunt PAs. We conclude that increased pulmonary blood flow induces an impairment of endothelium-dependent relaxation that is selective to PAs. The impaired relaxation may be mediated in part by excess superoxide production.

Topics: 3',5'-Cyclic-GMP Phosphodiesterases; Animals; Atrial Natriuretic Factor; Calcimycin; Disease Models, Animal; Endothelium, Vascular; Enzyme Inhibitors; Fetus; Guanylate Cyclase; Hypertension, Pulmonary; In Vitro Techniques; Muscle Relaxation; Muscle, Smooth, Vascular; Nitric Oxide Donors; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Phosphodiesterase Inhibitors; Pulmonary Artery; Pulmonary Circulation; Pulmonary Veins; Purinones; Sheep

Chronic hypoxic pulmonary hypertension (PH) is associated with vasoconstriction and structural remodeling of pulmonary vessels including narrowing of the arterial lumen and loss of distal functional arteries. To test whether lung overexpression of the angiogenic factor vascular endothelial growth factor (VEGF) is beneficial in hypoxic PH, recombinant adenovirus encoding the human VEGF 165 gene under the control of a cytomegalovirus promoter (Ad. VEGF) or control vector containing no gene in the expression cassette (Ad.Null) was administered intratracheally to rats. With Ad. VEGF (10(8) plaque-forming units [pfu]), VEGF protein was present in bronchoalveolar lavage fluid as early as 2 d and until 17 d after gene transfer, but was not detected in serum. Only small patchy areas of mononuclear cells without cell damage, edema, or hemorrhage were observed on lung histology with no significant change in lung permeability. In rats pretreated with Ad.VEGF (10(8) pfu) 2 d before a 2-wk exposure to hypoxia (10% O(2)), lower values versus Ad. Null-pretreated controls were found for pulmonary artery pressure (25 +/- 1 versus 30 +/- 2 mm Hg, P < 0.05), right ventricular over left ventricular-plus-septum weight (0.37 +/- 0.01 versus 0.47 +/- 0. 02, P < 0.001), normalized wall thickness of 50- to 200-microm vessels (P < 0.001), and muscularization of distal vessels (P < 0. 001). Pretreatment with Ad.VEGF (10(8) pfu) increased endothelial nitric oxide synthase activity in lung tissue and partially restored endothelium-dependent vasodilation in isolated lungs from chronically hypoxic rats, as assessed by improvement of ionophore A23187-induced vasodilation and attenuation of endothelin-1 (300 pmol)-induced vasoconstriction, an effect abolished in the presence of nitro-L-arginine methylester. We conclude that adenoviral-mediated VEGF overexpression in the lungs attenuates development of hypoxic PH, in part by protecting endothelium-dependent function.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Adenoviridae; Animals; Bronchoalveolar Lavage Fluid; Calcimycin; Capillary Permeability; DNA, Recombinant; Dose-Response Relationship, Drug; Endothelial Growth Factors; Endothelin-1; Gene Expression Regulation; Gene Transfer, Horizontal; Humans; Hypertension, Pulmonary; Hypoxia; In Vitro Techniques; Ionophores; Lung; Lymphokines; Nitric Oxide Synthase; Nitric Oxide Synthase Type III; Rats; Rats, Wistar; Time Factors; Vascular Endothelial Growth Factor A; Vascular Endothelial Growth Factors; Vasodilation

Among chicken strains, broilers are prone to pulmonary hypertension, whereas Leghorns are not. Relaxations to endothelium-dependent (ACh, A23187) and endothelium-independent [sodium nitroprusside (SNP), papaverine (PPV)] vasodilators were compared in preconstricted pulmonary artery (PA) rings from these chicken strains. ACh (10(-7), 10(-6), and 10(-5) M)- and A23187 (10(-6) and 10(-5.5) M)-induced relaxations were smaller (P < 0.05) in broilers than Leghorns. N(G)-nitro-L-arginine methyl ester (10(-3.5) M) caused similar reductions in ACh-induced relaxations in both strains. L-Arginine (10(-4) M) enhanced ACh-induced relaxations more in broilers than Leghorns. Relaxations to 10(-10)-10(-6) M SNP did not differ between strains, but were greater (P < 0.05) in broilers than Leghorns at higher concentrations (10(-5) and 10(-4) M). PPV (10(-4) M)- and SNP (10(-4) M)-induced maximal relaxations were greater in broilers than in Leghorns (176.2 +/- 14.7 vs. 120.9 +/- 14.7% and 201.3 +/- 7.8 vs. 171.2 +/- 10.7%, respectively, P < 0.05). Broiler PA rings appear to have increased intrinsic tone and reduced endothelium-derived nitric oxide activity, both of which may contribute to the susceptibility of broiler chickens to pulmonary hypertension.

Topics: Acetylcholine; Animals; Arginine; Calcimycin; Chickens; Disease Models, Animal; Endothelium, Vascular; Enzyme Inhibitors; Hypertension, Pulmonary; Ionophores; Male; NG-Nitroarginine Methyl Ester; Nitroprusside; Papaverine; Pulmonary Artery; Vasodilation; Vasodilator Agents

The management of sick newborn infants who have sustained a hypoxic insult is a common clinical problem but relatively little is known about the recovery process. The aim of this study was to investigate this process in newborn piglets.. Thirty five newborn piglets were exposed to chronic hypobaric hypoxia for three days, either from birth, three or 14 days of age, and were allowed to recover for one, three, or six days. Control animals of relevant age were also studied. The heart weight ratio and pulmonary arterial muscularity were measured. Endothelial dependent and independent relaxation of the isolated intrapulmonary conduit arteries was determined in classical organ chamber studies, together with measurement of basal and stimulated cGMP accumulation.. After six days of recovery the hypoxia induced right ventricular hypertrophy and pulmonary arterial medial hypertrophy had decreased in all animals but values were still abnormal in the two younger age groups. Relaxation was still impaired during the first three days of recovery in all groups, had normalised by six days in the two youngest groups, but relaxation (both endothelium dependent and independent) remained impaired in older animals. In these older animals basal nitric oxide (NO) production and basal and stimulated cGMP accumulation was normal.. The recovery of the smooth muscle cells lags behind that of the endothelial cells. A normal stimulated increase in cGMP with reduced relaxation suggests an altered threshold for cGMP effected relaxation. These findings help to explain why some hypoxic infants require protracted NO therapy.

Topics: Acetylcholine; Animals; Animals, Newborn; Calcimycin; Cyclic GMP; Enzyme Inhibitors; Hypertension, Pulmonary; Hypertrophy; Hypertrophy, Right Ventricular; Hypoxia; Nitric Oxide; omega-N-Methylarginine; Phosphodiesterase Inhibitors; Pulmonary Artery; Purinones; Swine; Tunica Intima; Vasoconstriction; Vasodilator Agents

Neonatal pulmonary hypertension is associated with increased pulmonary vascular reactivity. We studied the responses of isolated porcine intrapulmonary arteries after exposure of piglets to chronic hypobaric hypoxia (CHH) from 0 to 2.5, 3 to 6, or 14 to 17 days of age. CHH inhibited the postnatal development of endothelium-dependent vasorelaxation to acetylcholine (ACh) and the calcium ionophore A-23187. Basal accumulation of guanosine 3', 5'-cyclic monophosphate (cGMP) was unaffected, but cGMP response to ACh was inhibited. Endothelium-independent relaxation to nitric oxide (NO) and zaprinast (a phosphodiesterase inhibitor) was also inhibited, but cGMP accumulation in response to these agonists was normal. The ability of sodium nitroprusside (SNP) to cause vasorelaxation and increase cGMP accumulation was unaffected. Contractile responses to potassium chloride and prostaglandin F2 alpha (PGF2 alpha) were similar to normal after exposure from birth and 3 days and were decreased in the older group, but the ability of NG-monomethyl-L-arginine acetate to increase PGF2 alpha-induced contractions decreased. Thus exposure of newborn piglets to CHH causes 1) no increase in contractile responses and 2) impairment of endothelium-dependent and -independent relaxation by impairing signal transduction mechanisms involved in the release of NO and the effectiveness of cGMP.

Topics: Acetylcholine; Animals; Animals, Newborn; Atmospheric Pressure; Calcimycin; Chronic Disease; Cyclic GMP; Dinoprost; Endothelium, Vascular; Heart; Hypertension, Pulmonary; Hypoxia; In Vitro Techniques; Nitric Oxide; omega-N-Methylarginine; Potassium Chloride; Pulmonary Artery; Purinones; Swine; Vasodilation; Vasomotor System

Pulmonary arterial myocytes were cultured from normotensive and pulmonary hypertensive rats. Microfluorimetry of Ca2+ signals in fluo-3-loaded single myocytes at day 7 of culture was performed by a laser-scanned confocal imaging system. The resting level of cytoplasmic Ca2+ concentration ([Ca2+]i) in vascular myocytes obtained from hypertensive rats was higher than that in cultured myocytes obtained from normotensive rats. Angiotensin II elevated [Ca2+]i in the vascular myocytes cultured from both normotensive and hypertensive rats. However, a rise of [Ca2+]i induced by angiotensin II in the vascular myocytes obtained from pulmonary hypertensive rats was higher than that obtained from normotensive rats. On the other hand, the response of [Ca2+]i to A23187 did not differ between the vascular myocytes cultured from normotensive and hypertensive rats. The present results suggest that the resting and angiotensin II-responsive levels of [Ca2+]i in pulmonary arterial myocytes cultured from pulmonary hypertensive rats are higher than those cultured from normotensive rats.

Topics: Angiotensin II; Aniline Compounds; Animals; Calcimycin; Calcium; Cells, Cultured; Cytosol; Fluorescent Dyes; Hypertension, Pulmonary; Muscle, Smooth, Vascular; Pulmonary Artery; Rats; Vasoconstrictor Agents; Xanthenes

A major hemodynamic feature of acute lung injury is pulmonary hypertension caused by pulmonary vasoconstriction. Impairment of the mechanisms of pulmonary vasorelaxation may contribute to this pulmonary vasoconstriction. This study examined the effect of mesenteric ischemia/reperfusion (I/R) on lung neutrophil accumulation and endothelial-dependent and -independent cyclic 3'-5' guanosine monophosphate-mediated pulmonary vasorelaxation in rats.. Rats were studied after 1 hour of superior mesenteric artery occlusion and 2 hours of reperfusion. Lung neutrophil accumulation was determined by myeloperoxidase assay (MPO). The following mechanisms of pulmonary vasorelaxation were studied in isolated pulmonary artery rings by generating dose response curves (10(-9) to 10(-6)mol/L): (1) receptor-dependent, endothelial-dependent relaxation (response to acetylcholine), (2) receptor-independent, endothelial-dependent relaxation (response to the calcium ionophore, A23187), and (3) endothelial-independent relaxation (response to sodium nitroprusside [SNP]).. Lung MPO activity was significantly increased from 2.4 +/- 0.2 units/gm lung weight in controls to 10.3 +/- 0.4 after mesenteric I/R (p < 0.05). The vasorelaxation response to SNP was not different after mesenteric I/R, but vasorelaxation by both acetylcholine and A23187 were significantly impaired.. Endothelial-dependent pulmonary vasorelaxation is significantly impaired after mesenteric I/R. Such impairment of pulmonary vasorelaxation may help tip the net balance of pulmonary vasomotor tone toward vasoconstriction and contribute to the pulmonary hypertension seen in acute lung injury.

Topics: Acetylcholine; Animals; Calcimycin; Cyclic GMP; Endothelium, Vascular; Hypertension, Pulmonary; In Vitro Techniques; Lung; Lung Injury; Male; Neutrophils; Nitroprusside; Peroxidase; Pulmonary Artery; Pulmonary Circulation; Rats; Rats, Sprague-Dawley; Reperfusion Injury; Splanchnic Circulation; Vasodilation; Vasodilator Agents

Nitric oxide (NO) and endothelin-1 (ET-1) have both been implicated in the pathogenesis of pulmonary hypertension (PH). Therefore, we examined NO-related relaxation and ET-1 levels in rat hilar pulmonary arteries (PA) during the progression of monocrotaline (MCT)-induced PH.. Rats were studied 1 and 2 weeks after a single subcutaneous injection of MCT (80 mg/kg). Pulmonary artery pressure (PAP), right ventricular hypertrophy (RVH), NO-related relaxation and tissue ET-1 levels in PA were evaluated and compared with control (C).. One week post-MCT, endothelium (E)-dependent relaxation to 10(-5) M adenosine diphosphate (ADP), 10(-5) M A23187 and 10(-5) M acetylcholine (ACh) and tissue ET-1 levels in PA were normal. Rats in this group did not develop PH or RVH. Two weeks post-MCT, E-dependent relaxation was impaired (ADP, 7 +/- 3% VS. c, 62 +/- 5%; A23187, 2 +/- 7% vs. C, 58 +/- 2%; ACh, 33 +/- 7% vs. C, 86 +/- 2%; P < 0.05) and ET-1 levels were elevated (1925 +/- 244 pg/g wwt vs. C, 469 +/- 59 pg/g wwt, P < 0.05), In addition, significant PH and RVH were present (PAP 33 +/- 4 mmHg vs. C 18 +/- 0.8 mmHg, P < 0.05; RVH index 0.40 +/- 0.006 vs. C, 0.25 +/- 0.01, P < 0.05). Incubation with 10 microM indomethacin, 150 U/ml superoxide dismutase or 300 microM L-arginine failed to restore impaired relaxation to ACh. In E-intact rings, relaxation to 10(-6) M glyceryl trinitrate (GTN) was inhibited at 1 week post-MCT (72 +/- 2% vs. C, 87 +/- 3%, P < 0.05) with further inhibition at 2 weeks (39 +/- 4%). Response to GTN in E-denuded rings was normal in MCT groups.. These results indicate that MCT injection in rats results in delayed but progressive endothelial injury and PH. Despite mild endothelial dysfunction 1 week post-MCT, NO-related relaxation and ET-1 levels are normal. At 2 weeks post-MCT, inhibition of E-dependent NO-related relaxation and elevation of ET-1 levels are associated with PH and RVH. Thus inhibition of NO production associated with elevated ET-1 levels may play an important role in the pathophysiology of MCT-induced PH.

Topics: Acetylcholine; Adenosine Diphosphate; Animals; Arginine; Calcimycin; Dose-Response Relationship, Drug; Endothelins; Endothelium, Vascular; Hypertension, Pulmonary; Hypertrophy, Right Ventricular; In Vitro Techniques; Indomethacin; Male; Monocrotaline; Nitric Oxide; Nitroglycerin; Pulmonary Artery; Rats; Rats, Sprague-Dawley; Superoxide Dismutase; Vasodilation

We hypothesized that 5-lipoxygenase and cyclooxygenase products might be mediators of cardiopulmonary and systemic vascular effects induced by a 4 h continuous infusion of platelet-activating factor (PAF, 10 ng/kg/min) in anesthetized pigs. Indomethacin (cyclooxygenase inhibitor) potentiated and CGS 8515 (5-lipoxygenase inhibitor) attenuated PAF-induced increases in total peripheral resistance (TPR) from 2.5 to 4 h. However, the 5-lipoxygenase inhibitor failed to modify pulmonary vasoconstriction and hypertension caused by PAF. Except for a delay in onset (approximately 44 s) and rate of development of pulmonary hypertension during the initial 10 min of PAF infusion, the pulmonary hemodynamic changes were also not attenuated by indomethacin. On the other hand, at 4 h, the PAF-induced pulmonary hypertension and systemic vasoconstriction were completely or partially reversed, respectively, by WEB 2086 (PAF receptor antagonist). The PAF-induced increases in plasma thromboxane B2 (TXB2) were blocked by indomethacin but not by CGS 8515, and at 4 h the 5-lipoxygenase inhibitor potentiated the levels of TXB2 in pigs treated with PAF. The plasma concentrations of 6-keto-PGF1 alpha and leukotriene B4 (LTB4) were not modified by PAF or CGS 8515 + PAF. We conclude that PAF-induced increases in TPR (2.5-4 h) are potentiated by indomethacin and are dependent on 5-lipoxygenase products other than LTB4. Although the early pulmonary vascular response (< 10 min) to PAF is dependent on cyclooxygenase products, the sustained response (after 10 min) cannot be explained by either 5-lipoxygenase or cyclooxygenase products but may be mediated directly by PAF receptors.

Topics: 6-Ketoprostaglandin F1 alpha; Animals; Azepines; Blood; Calcimycin; Chromatography, High Pressure Liquid; Cyclooxygenase Inhibitors; Hemodynamics; Hypertension, Pulmonary; In Vitro Techniques; Indomethacin; Infusions, Intra-Arterial; Leukotriene B4; Lipoxygenase Inhibitors; Naphthoquinones; ortho-Aminobenzoates; Platelet Activating Factor; Swine; Thromboxane B2; Triazoles

The pulmonary vascular reactivity to endothelin-1 (ET-1) was assessed in rats previously exposed to 11% O2 (hypoxic) or room air (controls) for 3 weeks. In isolated control lung preparations studied during conditions of increased tone by U46619 (50 pmol/min) and treated with meclofenamate (3 microM), low doses of ET-1 (30 and 100 pM) reduced the pressor response to U46619 by 58 +/- 5% (p less than 0.01). Vasodilation induced by ET-1 was not abolished by the antagonist of endothelium-dependent relaxing factor (EDRF) NG-monomethyl-L-arginine (5 x 10(-4) M), which suppressed vasodilator response to ionophore A23187 (10(-8)-10(-7) M). Higher doses of ET-1 (300 and 1,000 pM) induced vasoconstriction during conditions of basal tone, and the pressor response to 300 pM ET-1 was enhanced by EDRF antagonists. Administration of ET-1 to lungs from hypoxic rats failed to cause pulmonary vasodilation and instead induced a greater pulmonary pressor response (300 pM) than in control rat lungs (7 +/- 1.5 vs. 1.6 +/- 0.5 mm Hg, p less than 0.01), which was not further potentiated by EDRF antagonists. Infusion of 300 pM ET to conscious catheterized animals induced a sustained increase in pulmonary resistance only in the hypoxic group (from 305 +/- 37 to 389 +/- 55 mm Hg/L/min, p less than 0.01) (n = 7). The results suggest that depending on the dose, ET-1 can cause pulmonary vasodilation (independent of EDRF release) or vasoconstriction (opposed by EDRF). During chronic hypoxic pulmonary hypertension, ET-1 behaves only as a pulmonary vasoconstrictor.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Arginine; Calcimycin; Endothelins; Hemodynamics; Hypertension, Pulmonary; Hypoxia; In Vitro Techniques; Male; Muscle Tonus; Nitric Oxide; omega-N-Methylarginine; Prostaglandin Endoperoxides, Synthetic; Pulmonary Circulation; Rats; Rats, Inbred Strains; Vasodilation

We recently described the early appearance of pulmonary hypertension in the fawn-hooded rat (FHR), an animal with platelet storage pool disease also known to develop systemic hypertension at later ages. Since mediators released from aggregating platelets influence vascular tone, we hypothesized that platelet-mediated pulmonary vascular responses in FHR may be abnormal and potentially linked to the mechanism of pulmonary hypertension. To test this we examined reactivity of isolated pulmonary arteries (PA) and thoracic aortas (Ao) from young FHR with moderately severe pulmonary hypertension but normal systemic pressures. These vessels were compared with PA and Ao from control Sprague-Dawley rat (SDR). Aggregating platelets (1,000-40,000 platelets/mm3) from FHR caused dilation of SDR PA and Ao but constriction of FHR PA and Ao. Qualitatively similar responses were also observed with platelets isolated from SDR implying that abnormal responses were not simply due to the storage pool deficiency in FHR. Response to the platelet-derived endothelium-dependent vasodilator ADP was markedly impaired in FHR PA and mildly impaired in FHR Ao. Endothelium-dependent dilation to acetylcholine, but not to A23187, was mildly impaired in FHR PA while responses to both dilators were normal in FHR Ao. Endothelium-independent dilation to sodium nitroprusside was normal in both FHR PA and Ao. Constrictor sensitivity to serotonin, but not to the thromboxane A2 mimetic U-46619, was increased in FHR PA while responses to both constrictors were normal in FHR Ao. In summary, PAs from FHR with spontaneous pulmonary hypertension exhibit paradoxical constriction to both normal and storage pool deficient platelets.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Acetylcholine; Adenosine Diphosphate; Animals; Aorta; Blood Platelets; Calcimycin; Cardiomegaly; Endothelium, Vascular; Hypertension, Pulmonary; Male; Meclofenamic Acid; Nitroprusside; Platelet Aggregation; Platelet Storage Pool Deficiency; Prostaglandin Endoperoxides, Synthetic; Pulmonary Artery; Rats; Rats, Inbred Strains; Serotonin; Vasoconstriction; Vasodilation

To determine whether exposure to chronic hypoxia and subsequent development of pulmonary hypertension induces alterations of endothelium-dependent relaxation in rat pulmonary vascular bed, we studied isolated lung preparations from rats exposed to either room air (controls) or hypoxia (H) during 1 wk (1W-H), 3 wk (3W-H), or 3W-H followed by 48 h recovery to room air (3WH + R). In lungs pretreated with meclofenamate (3 microM), the endothelium-dependent vasodilator responses to acetylcholine (10(-9)-10(-6) M) and ionophore A23187 (10(-9)-10(-7) M) were examined during conditions of increased tone by U46619 (50 pmol/min). Acetylcholine or A23187 produced dose-dependent vasodilation in control lungs, this response was reduced in group 1W-H (P less than 0.02), abolished in group 3W-H (P less than 0.001), and restored in group 3WH + R. In contrast, the endothelium-independent vasodilator agent sodium nitroprusside remained fully active in group 3W-H. The pressor response to 300 pM endothelin was greater in group 3W-H than in controls (6.8 +/- 0.5 mmHg vs. 1.6 +/- 0.2 mmHg, P less than 0.001) but was not potentiated by the endothelium-dependent relaxing factor (EDRF) antagonists: hydroquinone (10(-4) M); methylene blue (10(-4) M); and pyrogallol (3 x 10(-5) M) as it was in controls. It was similar to controls in group 3W-H + R. Our results demonstrate that hypoxia-induced pulmonary hypertension is associated with a loss of EDRF activity in pulmonary vessels, with a rapid recovery on return to a normoxic environment.

Topics: Acetylcholine; Animals; Blood Pressure; Calcimycin; Chronic Disease; Endothelins; Endothelium, Vascular; Hypertension, Pulmonary; Hypoxia; Male; Nitric Oxide; Nitroprusside; Pulmonary Circulation; Rats; Rats, Inbred Strains

Neonatal calves exposed to chronic hypobaric hypoxia develop severe pulmonary hypertension associated with altered vascular reactivity, cellular proliferation, and increased elastin and collagen production. We hypothesized that prostaglandin (PG) production would be decreased in the pulmonary arterial vessel wall of these calves. Further, because of the possibility that the hemodynamic stresses of hypoxic pulmonary hypertension might change along the longitudinal axis of the pulmonary circulation, we measured prostaglandin synthetic capability in tissues isolated from proximal pulmonary artery, distal pulmonary artery, and pulmonary vein. We found that PGI2 production was decreased in both proximal and distal pulmonary artery rings isolated from pulmonary hypertensive calves compared to controls. PGI2 production was greater in distal than in proximal lobar pulmonary artery. In contrast, pulmonary veins from hypertensive calves, which are protected from the hemodynamic stress of pulmonary arterial hypertension, did not demonstrate altered PGI2 production compared to controls. PGE2 production was also decreased in proximal hypertensive pulmonary arterial rings as compared to controls. To determine if this decrease in vessel wall production of prostaglandins was due to changes in cellular prostaglandin production, we studied prostaglandin production by the three major cell types comprising hypertensive and control arteries. Endothelial cells cultured from hypertensive main pulmonary artery produced less PGI2 than did those from control artery, and there appeared to be a shift from PGI2 production to PGE2 production in endothelial cells isolated from hypertensive artery. Explanted advential fibroblasts from hypertensive artery produced less PGE2 than did controls. Smooth muscle cell PGI2 production did not differ between cells isolated from hypertensive and control arteries in these brief 30-min incubations. We conclude that there is a relative deficit in PGI2 and PGE2 production in the pulmonary arteries of calves with hypoxia-induced pulmonary hypertension and speculate that this contributes to altered vascular tone and vessel remodeling.

Topics: Animals; Animals, Newborn; Calcimycin; Cattle; Cells, Cultured; Dinoprostone; Endothelium, Vascular; Epoprostenol; Fibroblasts; Hemodynamics; Hypertension, Pulmonary; Male; Muscle, Smooth, Vascular; Pulmonary Artery; Pulmonary Veins; Thromboxane B2

Staphylococcal alpha-toxin is known to damage mammalian cell membranes. Studies of erythrocytes indicate that the native toxin generates a discrete transmembrane channel with an effective diameter of 2-3 nm. (Füssle, R., S. Bhakdi, A. Szeigoleit, J. Tranum-Jensen, T. Kranz, and H.J. Wellensiek. 1981. J. Cell Biol. 91:83-94.) In isolated rabbit lungs, perfused with recirculating blood- and plasma-free perfusion fluid, the mediation of a toxin-provoked vascular pressor response by the triggering of the arachidonic acid cascade and its dependence on extracellular calcium were investigated. Dose-dependent pulmonary artery pressor responses were elicited by the injection of 0.5-5 micrograms staphylococcal alpha-toxin into the pulmonary artery. The pressor responses were completely abolished by preincubation of the toxin with neutralizing antibodies or by preformation of alpha-toxin hexamers in vitro. They were accompanied by the release of the arachidonic acid metabolites thromboxane B2 and 6-keto-prostaglandin F1 alpha (stable metabolites of thromboxane A2 and prostaglandin I2, respectively) into the perfusion fluid. They were blocked by inhibitors of thromboxane synthetase, cyclooxygenase, and phospholipase, as well as by substances that interfere with calcium-calmodulin function. alpha-Toxin induced selective release of potassium, but not lactatedehydrogenase into the medium. Calcium depletion of the intravascular space did not suppress the toxin-dependent potassium release but did abrogate the pressor response and the release of the arachidonic acid metabolites. When calcium was reintroduced into the circulation without the application of a second toxin stimulus, marked pressor responses paralleled by the release of arachidonic acid metabolites occurred. The conclusion drawn from these studies is that staphylococcal alpha-toxin provokes pulmonary vascular hypertension which is apparently mediated by thromboxane A2 formation, which surpasses the biological effect of the simultaneously formed prostaglandin I2. The triggering of the arachidonic acid cascade is strictly dependent on extracellular calcium and may be mediated by a nonphysiological calcium bypass through transmembrane toxin channels with subsequent stimulation of phospholipase activity.

Topics: Animals; Arachidonic Acid; Arachidonic Acids; Bacterial Toxins; Blood Pressure; Calcimycin; Calcium; Calcium Channel Blockers; Calmodulin; Gallic Acid; Hemolysin Proteins; Hypertension, Pulmonary; In Vitro Techniques; Indomethacin; Lung; Prostaglandins; Pulmonary Artery; Rabbits; Sulfonamides; Thromboxanes; Trifluoperazine