Effect of hypoxia on prostacyclin production in cultured pulmonary artery endothelium

The distinguishing cellular features of pulmonary artery smooth muscle cells from chronic thromboembolic pulmonary hypertension patients

In chronic thromboembolic pulmonary hypertension (CTEPH), central thrombi are the most likely disease initiators, and progressive pulmonary vascular remodeling, which is characterized by marked proliferation of pulmonary artery smooth muscle cells (PASMCs), may also contribute to the long-term progression of CTEPH. This study was designed to investigate the cellular characteristics of PASMCs isolated from the organized thrombotic tissues of CTEPH. In the present study, analysis of PASMCs isolated from five CTEPH patients and three control subjects showed that cells from CTEPH patients had certain characteristics that distinguished them from control cells, including inferior or no cell-cell contact inhibition growth, increased sensitivity to hypoxia-induced proliferation, resistance to serum starvation-induced apoptosis, and mitochondrial metabolism disorder. These differences in the PASMCs in endarterectomized tissue of CTEPH patients may prove useful in understanding the pathobiology of CTEPH.

Estradiol-17β and its cytochrome P450- and catechol-O-methyltransferase-derived metabolites selectively stimulate production of prostacyclin in uterine artery endothelial cells: role of estrogen receptor-α versus estrogen receptor-β

Metabolism of estradiol-17β to 2-hydroxyestradiol, 4-hydroxyestradiol, 2-methoxyestradiol, and 4-methoxyestradiol contributes importantly to the vascular effects of estradiol-17β in several vascular beds. However, little is known about the role of estradiol-17β metabolites via the different estrogen receptors (ER-α/ER-β) on de novo endothelial prostacyclin and thromboxane production. We hypothesized that estradiol-17β and its metabolites, via ER-α or ER-β, can enhance the prostacyclin/thromboxane ratio through the classic phospholipase A(2), cyclooxygenase-1, and prostacyclin synthase pathway in ovine uterine artery endothelial cells (UAECs) derived from pregnant (P-UAECs) versus nonpregnant (NP-UAECs) ewes. Western analyses showed higher expression of phospholipase A(2), cyclooxygenase-1, and prostacyclin synthase in UAECs from the pregnant state, whereas thromboxane synthase was lowered in UAECs from the pregnant state. In UAECs from the pregnant state, estradiol-17β, 2-hydroxyestradiol, 4-hydroxyestradiol, 2-methoxyestradiol and 4-methoxyestradiol concentration and time-dependently increased prostacyclin compared with controls. Prostacyclin increases in UAECs from the nonpregnant state were of a lower magnitude. Estradiol-17β and its metabolites stimulated higher prostacyclin/thromboxane ratios in UAECs from the pregnant state compared with UAECs from the nonpregnant state. Estradiol-17β-induced prostacyclin increases were abrogated by the antagonists SC-560 (cyclooxygenase-1), U-51605 (Prostacyclin synthase), ICI 182780 (ICI; both ER-α/β), and 1,3-bis(4-hydroxyphenyl)-4-methyl-5-[4-(2-piperidinyleth oxy)phenol]-1H-pyrazole dihydrochloride (MPP; ER-α), but not by 4-[2-phenyl-5,7-bis (trifluoromethyl) pyrazolo[1,5-a]pyrim idin-3-yl]phenol (PHTPP; ER-β). Prostacyclin increases induced by its metabolites were abolished by SC-560 and U-51605, but unaltered by ICI, MPP, or PHTPP. Our findings demonstrate that estrogen via primarily ER-α and its metabolites via ER-independent mechanisms influence the de novo endothelial biosynthesis of prostacyclin, which may be important in the regulation of vascular tone. These findings also shed light on the complexities of estrogen signaling via its metabolism and the functional heterogeneity of the ERs.

Pathobiology of pulmonary hypertension

A variety of conditions can lead to the development of pulmonary arterial hypertension (PAH). Current treatments can improve symptoms and reduce the severity of the hemodynamic abnormality, but most patients remain quite limited, and deterioration in their condition necessitates a lung transplant. This review discusses current experimental and clinical studies that investigate the pathobiology of PAH. An emerging theme is the consideration of ways in which one might reverse the advanced occlusive structural changes in the pulmonary circulation causing PAH. The current debate concerning the role of regeneration through stem cells is presented. This review also highlights investigations in a number of laboratories relating the pathobiology of PAH to mutations causing loss of function of bone morphogenetic protein receptor II in patients with familial PAH, as well as sporadic cases.

Functions of serotonin in hypoxic pulmonary vascular remodeling

In lung vasculature, reversible constriction of smooth muscle cells exists in response to acute decrease in oxygen levels (hypoxia). Progressive and irreversible structural remodeling that reduces blood vessel lumen takes place in response to chronic hypoxia and results in pulmonary hypertension. Several studies have shown a role of serotonin in regulating acute and chronic hypoxic responses. In this review the contribution of serotonin, its receptors and transporter in lung hypoxic responses is discussed. Hypoxic conditions modify plasma levels of serotonin, serotonin transporter activity, and expression of 5-HT1B and 5-HT2B receptors. These appear to be required for pulmonary vascular cell proliferation, which depends on the ratio between reactive oxygen species and nitric oxide. A heterozygous mutation was identified in the 5-HT2B receptor gene of a patient who developed pulmonary hypertension after fenfluramines anorexigen treatment. This C-terminus truncated 5-HT2B mutant receptor presents lower nitric oxide coupling, and higher cell proliferation capacity than the wild-type receptor. Under low oxygen tension, cells increase the transcription of specific genes via stabilization of the transcription factor hypoxia-inducible factor (HIF)-1. Factors such as angiotensin II or thrombin that can also control HIF-1 pathway contribute to pulmonary vascular remodeling. The 5-HT2B receptor via phosphatidylinositol-3 kinase/Akt activates nuclear factor-kappaB, which is involved in the regulation of HIF-1 expression. Acontrol of HIF- 1 by 5-HT2B receptors explains why expression of pulmonary vascular remodeling factors, such as endothelin-1 or transforming growth factor-beta, which is HIF-1-alpha regulated, is not modified in hypoxic 5-HT2B receptor mutant mice. Understanding the detailed mechanisms involved in lung hypoxic responses may provide general insight into pulmonary hypertension pathogenesis.

Role of NO and prostaglandins in acute hypoxic vasoconstriction in sheep pulmonary veins

The aim of this study was to investigate the effect of hypoxia on and the role of nitric oxide (NO) and cyclooxgenase inhibition in hypoxia-induced vasoconstriction in sheep isolated pulmonary veins. We used the potent pulmonary vasoconstrictor U46619, a thromboxane analog, as a precontractile agent. Our results showed that hypoxia caused a vasoconstriction both under resting tone and in U46619 (10(-6) mol/l) precontracted pulmonary veins. In the presence of the nonselective NO synthase inhibitior Nomega-nitro-L-arginine methyl ester (L-NAME; 3 x 10(-5) mol/l), the hypoxic pulmonary vasoconstriction (HPV) was significantly increased in veins under resting force. However, there was a decrease in HPV in pulmonary veins precontracted with U46619 in the presence of L-NAME. Moreover, L-NAME markedly augmented the U46619-induced pulmonary contractions under normoxic conditions. Cyclooxygenase inhibition with indomethacin (10(-5) mol/l) significantly reduced the HPV both under resting tone and in precontracted veins. Indomethacin also significantly decreased the U46619-induced pulmonary contractions prior to the induction of hypoxia. Our findings suggest that NO and prostaglandins can act as a modulators of the hypoxic vasoconstriction in isolated pulmonary veins.

Hypoxic pulmonary vasoconstriction in cardiothoracic surgery: basic mechanisms to potential therapies

Hypoxic pulmonary vasoconstriction is postulated to be an adaptive mechanism to match lung perfusion with ventilation; however, the consequences of the maladaptive effects of pulmonary vasoconstriction represent formidable therapeutic challenges. Understanding the basic mechanisms of hypoxic pulmonary vasoconstriction will enhance the assimilation of translational research into clinical practice. The purposes of this review are to (1) define basic mechanisms of pulmonary vasoconstriction and vasorelaxation; (2) delineate the biphasic contractile response to hypoxia; (3) critically examine data that support the mediator hypothesis versus the ion channel hypothesis; and (4) explore potential mechanistic-based therapies for hypoxic pulmonary vasoconstriction.

Human microvascular endothelial cell prostaglandin E1 synthesis during in vitro ischemia-reperfusion

Ischemia-reperfusion injury is a microvascular event documented in numerous in vivo animal models. In animal models, prostaglandin and prostaglandin analogues have been found to ameliorate reperfusion injury. These studies were undertaken to evaluate human microvascular endothelial PGE(1) synthesis during in vitro ischemia followed by reperfusion. Human (neonatal) microvascular endothelial cell (MEC) cultures (n = 6) were subjected to sequential 2 h periods of normoxia (20% O(2)), ischemia (1.5% O(2)), and reperfusion (20% O(2)). Prostaglandin E(2) synthesis in conditioned media was determined by ELISA. Steady state levels of MEC prostaglandin H synthase (PGHS)-1 and -2 mRNA were assessed at the end of each 2-h period using RT-PCR and a quantitative mRNA ELISA. MEC PGHS protein levels were analyzed using an ELISA. PGE(1) release increased significantly during the initial 30 min of ischemia, but rapidly fell below normoxic levels by 90 and 120 min. During reperfusion, PGE(1) release returned to normoxic levels at 30, 60, and 90 min, and exceeded normoxic levels at 120 min. PGHS-1 mRNA levels were undetectable during all experimental conditions. PGHS-2 mRNA levels were unchanged by ischemia, but were decreased by reperfusion. In contrast, PGHS-2 protein levels increased 3-fold during ischemia, and remained elevated during reperfusion. Human MEC do not express PGHS-1 mRNA in vitro. Prolonged ischemia decreases MEC PGE(1) synthesis, and stimulates increased PGHS-2 protein levels without altering the steady state levels of COX-2 mRNA. During reperfusion, increased PGHS-2 protein levels persist and are associated with stimulated PGE(2) secretion, despite relative decreases in PGHS-2 mRNA.

Pathophysiology of pulmonary hypertension due to lung disease

Pulmonary hypertension (PH) often complicates the course of patients with advanced lung disease, and it is associated with a worse prognosis. Per the recent classification of pulmonary hypertensive disorders, PH due to lung disease is considered as a separate category within a group of disorders that was previously referred to as "secondary" PH. Among the lung diseases associated with PH, the incidence and clinical course of PH is best known for patients with COPD. Per studies in patients with COPD and other lung disorders, it is evident that the pathophysiology and treatment of these disorders is generally distinct from that of pulmonary arterial hypertensive disorders. Changes in the pulmonary vasculature that accompany elevations in pulmonary vascular pressure are generally referred to as pulmonary vascular remodeling. Chronic hypoxia is well known to cause pulmonary vascular remodeling and PH, and it is the major mechanism implicated for the development of PH in patients with lung disease. Other mediators have also been implicated in the pathogenesis of PH in animal models and patients with PH, including patients with pulmonary diseases. General features of pulmonary vascular remodeling are discussed with particular emphasis on those changes that have been described in patients with lung diseases. Recent discoveries in these areas are also reviewed, and findings in pulmonary arterial hypertensive diseases are contrasted with those found in patients with PH due to lung diseases. Some of these discoveries have already led to new treatment strategies for patients with the most severe forms of PH. PH due to lung diseases shares some common pathophysiologic features with pulmonary arterial hypertension. Therefore, it is likely that these discoveries and new treatments will also be extended to benefit patients with PH due to lung disease.

Molecular and cellular basis of pulmonary vascular remodeling in pulmonary hypertension

Clinical pulmonary hypertension is characterized by a sustained elevation in pulmonary arterial pressure. Pulmonary vascular remodeling involves structural changes in the normal architecture of the walls of pulmonary arteries. The process of vascular remodeling can occur as a primary response to injury, or stimulus such as hypoxia, within the resistance vessels of the lung. Alternatively, the changes seen in more proximal vessels may arise secondary to a sustained increase in intravascular pressure. To withstand the chronic increase in intraluminal pressure, the vessel wall becomes thickened and stronger. This "armouring" of the vessel wall with extra-smooth muscle and extracellular matrix leads to a decrease in lumen diameter and reduced capacity for vasodilatation. This maladaptive response results in increased pulmonary vascular resistance and consequently, sustained pulmonary hypertension. The process of pulmonary vascular remodeling involves all layers of the vessel wall and is complicated by the finding that cellular heterogeneity exists within the traditional compartments of the vascular wall: intima, media, and adventitia. In addition, the developmental stage of the organism greatly modifies the response of the pulmonary circulation to injury. This review focuses on the latest advances in our knowledge of these processes as they relate to specific forms of pulmonary hypertension and particularly in the light of recent genetic studies that have identified specific pathways involved in the pathogenesis of severe pulmonary hypertension.

Multiple sites of oxygen sensing and their contributions to hypoxic pulmonary vasoconstriction

Oxygen sensing by the pulmonary vasculature is important for the regulation of vessel tone and the matching of lung perfusion to ventilation. Airways hypoxia is a major stimulus for vasoconstriction, which diverts blood from hypoxic alveoli to better ventilated areas of the lung. Several hypotheses have emerged to explain how pulmonary arteries sense a decrease in oxygen and mediate hypoxic pulmonary vasoconstriction (HPV). They differ mainly in where they place the main site of HPV: in the endothelial or smooth muscle cells of the artery wall. HPV probably results from synergistic actions on both cell types, but it can proceed in the absence of endothelium, suggesting that the primary oxygen sensor is the smooth muscle cell and endothelium-derived agents modulate the muscle response. Several oxygen-sensing targets have been identified in smooth muscle, including potassium channels, Ca(2+) stores in the sarcoplasmic reticulum (SR) and the Ca(2+) sensitivity of the contractile proteins. The evidence for different oxygen-sensing mechanisms in pulmonary vessels is discussed.

Pulmonary vascular remodeling: a target for therapeutic intervention in pulmonary hypertension

Pulmonary vascular remodelling is an important pathological feature of pulmonary hypertension, leading to increased pulmonary vascular resistance and reduced compliance. It involves thickening of all three layers of the blood vessel wall (due to hypertrophy and/or hyperplasia of the predominant cell type within each layer), as well as extracellular matrix deposition. Neomuscularisation of non-muscular arteries and formation of plexiform and neointimal lesions also occur. Stimuli responsible for remodelling involve transmural pressure, stretch, shear stress, hypoxia, various mediators [angiotensin II, endothelin (ET)-1, 5-hydroxytryptamine, growth factors, and inflammatory cytokines], increased serine elastase activity, and tenascin-C. In addition, there are reductions in the endothelium-derived antimitogenic substances, nitric oxide, and prostacyclin. Intracellular signalling mechanisms involved in pulmonary vascular remodelling include elevations in intracellular Ca2+ and activation of the phosphatidylinositol pathway, protein kinase C, and mitogen-activated protein kinase. In animal models of pulmonary hypertension, various drugs have been shown to attenuate pulmonary vascular remodelling. These include angiotensin-converting enzyme inhibitors, angiotensin receptor antagonists, ET receptor antagonists, ET-converting enzyme inhibitors, nitric oxide, phosphodiesterase 5 inhibitors, prostacyclin, Ca2+ -channel antagonists, heparin, and serine elastase inhibitors. Inhibition of remodelling is generally accompanied by reductions in pulmonary artery pressure. The efficacy of some of the drugs varies, depending on the animal model of the disease. In view of the complexity of the remodelling process and the diverse aetiology of pulmonary hypertension in humans, it is to be anticipated that successful anti-remodelling therapy in the clinic will require a range of different drug options.

Inhibition of prostanoid-mediated contraction to endothelin-1 after hypoxia in rat aorta

The role of the thromboxane A(2)/prostaglandin H(2) receptor in endothelin-1 contraction was investigated in aortic rings from rats exposed to normoxia (21% O(2)) or hypoxia (10% O(2)) for 12 h. Indomethacin (10 microM) and SQ 29,548 (0.1 microM, thromboxane A(2)/prostaglandin H(2) receptor antagonist) reduced maximum tension and increased EC(50) in endothelium-intact and -denuded rings from normoxic animals. Neither inhibitor had any effect on rings from hypoxic rats. Thromboxane A(2) and/or prostaglandin H(2) contribute to the response to endothelin-1 in aortas from normoxic rats but not from rats exposed to hypoxia. Loss of prostanoid-enhancement of endothelin-1 contraction contributes to impair vascular reactivity after hypoxia.

Induction of endothelial cell cytoplasmic lipid bodies during hypoxia

Lipid bodies (LBs), lipid-rich cytoplasmic inclusions found in many cell types, seem to act as nonmembrane sites of eicosanoid formation. Because alterations in eicosanoid products have been demonstrated in endothelial cells (ECs) during hypoxia, we investigated induction of LBs in systemic and pulmonary ECs exposed to acute and/or chronic hypoxia. LBs in ECs were O(2)-concentration dependent, increasing approximately fivefold during acute exposure to 0% O(2) in both cell types. During chronic exposure to 3% O(2), LBs were induced only in systemic ECs. LBs were not induced by other cellular stresses (heat shock or glucose deprivation). Subsequent studies suggested that protein kinase C-dependent and tyrosine kinase-dependent pathways are important in LB induction during hypoxia. PGH synthase was demonstrated in LBs in every case in which they were induced. These are the initial studies to demonstrate induction of LBs in ECs and to demonstrate LB induction during exposure to hypoxia in any cell type. These results imply that in ECs, LBs are structurally distinct inducible sites for synthesis of eicosanoid mediators.

Hypoxic pulmonary vasoconstriction

Hypoxic vasoconstriction is unique to pulmonary circulation. The pulmonary response is part of a self-regulatory mechanism by which pulmonary capillary blood flow is automatically adjusted to alveolar ventilation for maintaining the optimal balance of ventilation and perfusion. In pathological conditions, hypoxic pulmonary vasoconstriction may occur as an acute episode or as a sustained response with pulmonary hypertension and vascular remodeling. Vasoactive substances produced from the endothelial cells (prostanoids, nitric oxide, or endothelin) or other mediators such as 5 hydroxytryptamine have been examined as possible mediators of hypoxic vasoconstriction. These appear more likely to be modulators than mediators of the vasoconstrictor response to hypoxia. Recent hypotheses have emerged indicating that O2 levels per se can regulate ion channel activity. The modulation of both K+ and Ca2+ channels differs according to the conduit or resistance pulmonary vessel type, tending to extend the former and contract the latter, thereby opposing the ventilation to perfusion mismatching. In the absence of drugs that act selectively on pulmonary circulation, inhaled therapy is an alternative in the treatment of pulmonary hypertension. According to its short half-life and to its potential cytotoxicity, nitric oxide is only of value in the management of patients with acute respiratory disease. Aerosolized prostacyclin and iloprost result in a sustained efficacy of the inhaled vasodilator regimen in patients with severe pulmonary hypertension and offer a new strategy for treatment of this disease. At the moment, therapy aimed at reversing the structural remodeling and matrix deposition in pulmonary arteries remains experimental. New drugs such as potassium channel openers or endothelin receptor antagonists warrant further investigations as possible therapeutic candidates in the treatment of pulmonary hypertension.

Prostanoid production in rabbit corpus cavernosum: I. regulation by oxygen tension

PURPOSE

To investigate the effects of oxygen tension on prostanoid synthesis in rabbit penile corpus cavernosum tissue (RCC) in organ culture.

MATERIALS AND METHODS

Strips of rabbit corpus cavernosum were incubated in organ culture media under varying oxygen conditions (0%, 12% and 21% oxygen), in the presence or absence of acetylcholine and arachidonate stimulation. Prostanoids were measured in collected media by radioimmunoassay. Prostaglandin H synthase (PGHS) protein levels and mRNA PGHS expression were measured under both 0% and 21% oxygen conditions.

RESULTS

Basal and acetylcholine-stimulated PGI2 release was progressively diminished as a function of diminishing oxygen tension (pO2 from approximately 165 to 25 mm.Hg). The basal and stimulated production of other prostanoids, thromboxane A2, PGF2alpha, and PGE2, was also significantly inhibited under 0% oxygen (approximately 25 mm.Hg) conditions. However, incubation under 0% oxygen did not alter PGHS protein levels nor mRNA PGHS expression. Cavernosal strips incubated under 0% oxygen but supplemented with exogenous arachidonate (10 microM.) maintained significantly lower PGI2 production than tissues exposed to 21% oxygen (approximately 165 mm.Hg).

CONCLUSIONS

These data demonstrate that oxygen tension regulates prostaglandin production in corporal tissue. The reduction in prostanoid production during hypoxia can be attributed to inhibition of PGHS activity rather than the expression of the enzyme. In view of the role of PGI2 as an inhibitor of platelet aggregation and white cell-endothelial adhesion, our findings may provide mechanistic insight into the alteration in corporal blood homeostasis ischemic-hypoxic priapism.

Heterogeneity in prostacyclin and thromboxane synthesis in ovine pulmonary vascular tree: effect of age and oxygen tension

Intrapulmonary arteries and veins of 8 near-term fetal lambs (141-145 days gestation) and 8 ewes were isolated into segments of > 3mm, 1-3 mm, and < mm in diameter. Vessels were incubated in Krebs' buffer at 37 degrees C at PO2 approximately 100 torr (normoxia) and PO2 < 50 torr (hypoxia) to study local vascular production of prostanoids. Prostacyclin and thromboxane (Tx) A2 produced were measured by radioimmunoassay and expressed in ng/mg dry wt, means +/- SEM. During normoxia, fetal arteries > 3 mm synthesized more prostacyclin than adult arteries of the same size (1.71 +/- 0.3 vs 0.45 +/- 0.04). However, fetal arteries < 1 mm synthesized less prostacyclin than adult arteries < 1 mm (0.47 +/- 0.1 vs 1.75 +/- 0.16). Prostacyclin production by veins > 3 mm was similar in the fetus and adult (0.49 +/- 0.06 vs 0.67 +/- 0.08), but in veins < 1 mm was greater in adult than in fetal vessels (1.73 +/- 0.17 0.54 +/- 0.06). Hypoxia-attenuated prostacyclin production by fetal arteries and veins of all sizes, but only in 1 to 3-mm-size adult arteries. In general, production of TxA2 by segments of fetal and adult vessels was less than 50% of that of prostacyclin. Protein and DNA concentrations in similar sized fetal and adult vessels were similar. The data show that there is heterogeneity in the production of prostacyclin and TxA2 along the ovine pulmonary vascular tree. Prostanoid synthesis of fetal vessels is markedly influenced by hypoxia, with a greater suppression of prostacyclin synthesis. Similar protein and DNA concentrations in fetal and adult vessels suggest that differences in prostanoid production by vessel segments may be due to differences in enzyme activity rather than cell number or tissue mass.

Persistent Pulmonary Hypertension of the Newborn: Role of Nitric Oxide

Persistent pulmonary hypertension of the newborn (PPHN) is a common cause of respiratory failure in the full-term neonate. Molecular and cellular studies in vascular biology have revealed that endothelial-derived mediators play a critical role in the pathogenesis and treatment of PPHN. Endothelial-derived vasoconstrictors, like endothelin, may increase smooth muscle cell contractility and growth, leading to the physiologic and structural changes observed in the pulmonary arterioles of infants with this disease. On the other hand, decreased production of the endothelial-derived relaxing factor, nitric oxide, may exacerbate pulmonary vasoreactivity and lead to more severe pulmonary hypertension. Exogenous (inhaled) nitric oxide therapy reduces pulmonary vascular resistance and improves oxygenation. The safety and efficacy of this therapy in reducing the need for extracorporeal membrane oxygenation and decreasing long-term morbidity is being tested in several trials nationally and abroad. Understanding the basic mechanisms that regulate the gene expression and production of these vasoactive mediators will lead to improved preventive and therapeutic strategies for PPHN.

Hypoxia stimulates prostacyclin synthesis in newborn pulmonary artery endothelium by increasing cyclooxygenase-1 protein

In newborn lambs, pulmonary prostacyclin (PGI2) production increases acutely in response to low oxygen. We tested the hypothesis that decreased oxygenation directly stimulates PGI2 synthesis in arterial segments and cultured endothelial cells from newborn lamb intrapulmonary arteries. In segments studied at PO2 of 680 mm Hg, the synthesis of PGI2 exceeded prostaglandin E2 (PGE2) by 73%. Endothelium removal lowered PGI2 by 77% and PGE2 by 66%. At low oxygen tension (PO2, 40 mm Hg), PGI2 and PGE2 synthesis rose by 96% and 102%, respectively. Similarly, in endothelial cells studied at PO2 of 680 mm Hg, the synthesis of PGI2 exceeded PGE2 by 50%, and at low oxygen tension both PGI2 and PGE2 increased (89% and 64%, respectively). Endothelial cell PGI2 synthesis maximally stimulated by bradykinin, A23187, or arachidonic acid was also increased at low PO2 by 50%, 66%, and 48%, respectively. PGE2 synthesis was similarly altered, increasing by 33%, 37%, and 41%, respectively. In contrast, lowering oxygen had minimal effect on PGI2 and PGE2 synthesis with exogenous PGH2, which is the product of cyclooxygenase. Immunoblot analyses revealed that there was a 2.6-fold greater abundance of cyclooxygenase-1 protein at PO2 of 40 versus 680 mm Hg, and the increase at lower oxygen tension was inhibited by cycloheximide. The cyclooxygenase-2 isoform was not detected. Thus, attenuated oxygenation directly stimulates PGI2 and PGE2 synthesis in intrapulmonary arterial segments and endothelial cells from newborn lambs. This process is due to enhanced cyclooxygenase activity related to increased abundance of the cyclooxygenase-1 protein, and this effect may be due to increased synthesis of the enzyme protein.

In vitro effects of hypoxia and reoxygenation on human umbilical endothelial cells

We investigated metabolic changes in human umbilical venous endothelial cells, when these were incubated under hypoxic followed by hyperoxic conditions, thus simulating hypoxia and reoxygenation. The human umbilical venous endothelial cells were incubated with a degassed buffer (oxygen content: 0-0.5%) for either 3 h or 24 h, followed by a 60 min incubation with oxygen-perfused buffer (oxygen content: 100%). Three hours of hypoxia led to a slight decrease in the ATP and creatine phosphate content (-16% +/- 5%), while a pronounced decrease of high energy phosphates (-54% +/- 4%) was observed after 24 h of hypoxia. Reoxygenating the cells after 3 h of hypoxia led to restoration of the content of high energy phosphates, while reoxygenation after 24 h resulted in a strong decrease (-66% +/- 4%). The prostaglandin I2 release during the first 3 h of hypoxia exceeded the release in the following 21 h. In all cases, reoxygenation increased the prostaglandin I2 release. Under normoxic conditions the ratio between oxidised glutathione and reduced glutathione shifted from 1:100 to 1:4.5 after 3 h of hypoxia. The content of lipid peroxidation products was almost unaffected during hypoxia, whereas reoxygenation resulted in a pronounced increase (+380% +/- 60%). The results of this in vitro study suggest that relatively long periods of hypoxia lead to a deficiency of high energy phosphates in the cell. Reoxygenation leads to the formation of oxygen-derived radicals, irrespectively of a prior hypoxia.

Effect of hypoxia on release of vasoactive substances from cultured pulmonary arterial and aortic endothelial cells

The effect of hypoxia on the production and release of vasoactive substances from endothelial cells of pulmonary artery (PAECs) and aorta (AECs) was studied. The results indicated that the overall effect of the long half-life vasoactive substances released from PAECs and AECs was vasoconstrictive. The long half-life lipid-soluble substances produced by PAECs and AECs were vasodilative, and did not change in hypoxia. However, the long half-life water-soluble heat-unstable and heat-stable ones were vasoconstrictive. Hypoxia could reduce the release of the former and promote that of the latter which might be peptides. The PAECs could release specific long half-life mediator which was pulmonary artery-constrictive, water-soluble, heat-unstable, and not related to hypoxia. Hypoxia inhibited the production of PGI2, a short half-life vasodilator, in PAECs, but not in AECs.

Stimulation of prostaglandin synthesis by human endothelial cells exposed to hypoxia

In ischemic organs, arachidonic acid (AA) metabolites and mostly prostaglandins (PGs) have been found to be released in high amounts. The mechanism for this AA metabolism activation and its physiological implications are not clear. Because endothelial cells are an important source of PGs and because they seem to be very rapidly affected by ischemia, we developed an in vitro model where human endothelial cells were submitted to hypoxia. An important specific activation of phospholipase A2 was observed during hypoxia, which was concomitant with a rise in cytosolic calcium concentration. Endothelial cells synthetize in normal conditions as a mean 1.42, 1.00, 7.69, and 26.92 ng/mg proteins of, respectively, PGE2, PGD2, PGF2 alpha, PGI2. An important increase of about five- to ninefold in the synthesis of the four PGs was observed during hypoxia, which followed the same kinetics as the PLA2 activation. This increase in PG synthesis was sensitive to cyclooxygenase inhibitors. During reoxygenation, PG synthesis decreased back to the basal level of resting cells, suggesting that cells were able to recover their homeostasis after hypoxia. These observations indicate that endothelial cells exposed to oxygen deprivation are a major source of PGs and could contribute to the high amounts of PG released in vivo in ischemic organs.

Hypoxia induces lymphocyte adhesion to human mesenchymal cells via an LFA-1-dependent mechanism

We and others have previously reported that mesenchymal cells, including endothelial and muscle cells, sense oxygen tension and respond in a specific way during exposure to hypoxic environment. We have examined the interactions of human muscle and endothelial cells, which have been exposed to hypoxic environments, with T and B lymphoid cell lines and peripheral blood lymphocytes (PBL), not subjected to hypoxia. The adhesion of B lymphocyte cell line (JY) and the adhesion of T lymphocyte cell line (Jurkat) to muscle cell monolayers that had been incubated at PO2 of 50 Torr for 3 h increased more than four- and twofold, respectively. Hypoxia appears to upregulate a saturable muscle cell-associated adhesion mechanism, which is capable of withstanding distraction forces greater than 45 g, and is inhibitable by LFA-1-specific monoclonal antibodies (MAbs). Hypoxia also induced a reciprocal decrease in lymphocyte-muscle cell adhesion mechanisms inhibitable by VCAM-1- or VLA-4-specific MAbs. Cultured human endothelial cells when subjected to hypoxic conditions also increased their adhesion for lymphoid cells and cell lines. This induction of adhesion could again be attenuated by anti-LFA-1, but not by anti-ICAM-1 MAb, suggesting that hypoxia activates an adhesion molecule on human mesenchymal cells that is likely to be a new ligand for LFA-1. This report is the first demonstration of a direct induction of cell adhesion mechanisms by hypoxic environments.

The role of endothelium in hypoxic constriction of human pulmonary artery rings

The aim of the study was to elucidate the mechanism of the contraction produced by hypoxia in human intrapulmonary artery rings. Hypoxia (5 mm Hg) produced a contraction that was greater when the artery rings were precontracted (with endothelin-1) than when recorded under optimal resting force. The contraction was similar in small-diameter (0.38 to 0.68 mm) and in large-diameter (2.2 to 4.5 mm) artery rings under resting force. Removal of the endothelium markedly reduced or abolished the hypoxic contraction in precontracted artery rings (large diameter, 26 +/- 9 to -7 +/- 4 g cm-2) or under optimal resting force. Hypoxia markedly reduced or abolished the acetylcholine-induced relaxation in precontracted artery rings without affecting relaxation produced by sodium nitroprusside. Flurbiprofen caused a slight contraction itself (large diameter, 10 +/- 3 g cm-2) and significantly inhibited the contraction produced by hypoxia both under resting force (8 +/- 2 to 2 +/- 1 g cm-2) and in precontracted artery rings (18 +/- 2 to 1 +/- 1 g cm-2). Verapamil had no significant effect on the hypoxic contraction either under resting force or when precontracted. It is concluded that hypoxic contraction of human pulmonary artery rings depends on the presence of endothelium and is partly due to inhibition of a vasodilator cyclooxygenase product.

Oxygen modulates prostacyclin synthesis in ovine fetal pulmonary arteries by an effect on cyclooxygenase

Prostacyclin (PGI2) plays an integral role in O2 mediation of pulmonary vasomotor tone in the fetus and newborn. We hypothesized that O2 modulates PGI2 synthesis in vitro in ovine fetal intrapulmonary arteries, with decreasing O2 causing attenuated synthesis. A decline in PO2 from 680 to 40 mmHg caused a 26% fall in basal PGI2 synthesis. PGI2 synthesis maximally stimulated by bradykinin, A23187, and arachidonic acid were also attenuated at low PO2, by 35%, 33%, and 35%, respectively. PGE2 synthesis was equally affected. In contrast, varying O2 did not alter PGI2 synthesis with exogenous PGH2, which is the product of cyclooxygenase and the substrate for prostacyclin synthetase. Prostaglandin-mediated effects of O2 on cAMP production were also examined. Decreasing PO2 to 40 mmHg caused complete inhibition of basal cAMP production, whereas cAMP production stimulated by exogenous PGI2 was not affected. In parallel studies of mesenteric arteries, PGI2 synthesis and cAMP production were enhanced at low O2. Thus, PGI2 synthesis in fetal intrapulmonary arteries is modulated by changes in O2, with decreasing O2 causing attenuated synthesis. This process is due to an effect on cyclooxygenase activity, it causes marked parallel alterations in cAMP production, and it is specific to the pulmonary circulation.

Acute hypoxia alters eicosanoid production of perfused pulmonary artery endothelial cells in culture

Hypoxia alters vascular tone which regulates regional blood flow in the pulmonary circulation. Endothelial derived eicosanoids alter vascular tone and blood flow and have been implicated as modulators of hypoxic pulmonary vasoconstriction. Eicosanoid production was measured in cultured bovine pulmonary endothelial cells during constant flow and pressure perfusion at two oxygen tensions (hypoxia: 4% O2, 5% CO2, 91% N2; normoxia: 21% O2, 5% CO2, 74% N2). Endothelial cells were grown to confluence on microcarrier beads. Cell cartridges (N = 8) containing 2 ml of microcarrier beads (congruent to 5 x 10(6) cells) were constantly perfused (3 ml/min) with Krebs' solutions (pH 7.4, T 37 degrees C) equilibrated with each gas mixture. After a ten minute equilibration period, lipids were extracted (C18 Sep Pak) from twenty minute aliquots of perfusate over three hours (nine aliquots per cartridge). Eicosanoids (6-keto PGF1 alpha; TXB2; and total leukotriene [LT - LTC4, LTD4, LTE4, LTF4]) were assayed by radioimmunoassay. Eicosanoid production did not vary over time. 6-keto PGF1 alpha production was increased during hypoxia (normoxia 291 +/- 27 vs hypoxia 395 +/- 35 ng/min/gm protein; p less than 0.01). Thromboxane production (normoxia 19 +/- 2 vs hypoxia 20 +/- 2 ng/min/gm protein) and total leukotriene production (normoxia 363 +/- 35 vs hypoxia 329 +/- 29 ng/min/gm protein) did not change with hypoxia. These data demonstrated that oxygen increased endothelial prostacyclin production but did not effect thromboxane or leukotriene production.

Pharmacological evidence for the role of mediators in hypoxia-induced vasoconstriction in sheep isolated intrapulmonary artery rings

The aim of this study was to determine the likely mediator(s) involved in the hypoxic-induced contraction in sheep pulmonary artery rings in vitro by studying the effects of selective receptor antagonists and enzyme inhibitors. Hypoxia caused a contraction in arteries under resting force and when precontracted with 5-hydroxytryptamine (5-HT). Flurbiprofen, a cyclooxygenase inhibitor, reduced the hypoxic contraction in 5-HT-precontracted rings but augmented the first part of the hypoxic contraction under baseline force. Inhibition of nitric oxide by haemolysate increased the hypoxic contraction under resting force. Superoxide dismutase and N-t-butyl-alpha-phenylnitrone (PBN), free radical scavenging agents, and trypsin, a proteolytic enzyme, did not produce any significant effect on hypoxia-induced constriction. Propranolol plus phentolamine, beta- and alpha-adrenoceptor antagonists respectively, did not produce any effect on hypoxic contraction under resting force, whereas these antagonists augmented hypoxic contraction in the presence of 5-HT. This combination of antagonists also caused a reduction of 5-HT contraction which was the result of alpha 2-adrenoceptor blockade. Verapamil, a calcium channel blocking drug, significantly reduced the 5-HT contraction, but did not reduce that caused by hypoxia either under resting force or in precontracted rings. These results suggest that hypoxic constriction in sheep isolated intrapulmonary artery is in part caused by reduced release of vasodilator prostanoids. This contraction does not involve voltage-operated calcium channels and is limited by release of endothelium-derived nitric oxide.

Prostacyclin production and mediation of adenylate cyclase activity in the pulmonary artery. Alterations after prolonged hypoxia in the rat

Prostacyclin is a critical mediator of structure and function in the pulmonary circulation, causing both the inhibition of vascular smooth muscle growth and vasodilation via the stimulation of adenylate cyclase. To examine the potential role of alterations in prostacyclin production or mechanism of action in chronic hypoxic pulmonary hypertension, we determined the effects of prolonged (7 d) in vivo hypoxia on in vitro prostacyclin synthesis and mediation of adenylate cyclase activity in rat main pulmonary arteries. In control arteries prostacyclin production exceeded that of prostaglandin (PG) E2 by 25-fold, with 42% originating from the endothelium. Studies utilizing indomethacin revealed that endogenous prostaglandins mediate at least 69% of basal adenylate cyclase activity. Prostacyclin-stimulated enzyme activity was enhanced by exogenous GTP, indicating that this is a receptor-mediated process involving G protein amplification. Comparable dose-related responses to prostacyclin and PGE2 suggest that these agents may activate a common receptor. After 7 d of in vivo hypoxia there was a 2.7-fold increase in in vitro prostacyclin production, with equivalent increases in synthesis in the endothelium and vascular smooth muscle. However, despite this increase there was no change in basal adenylate cyclase activity, and this was associated with attenuated sensitivity of the enzyme to prostacyclin stimulation. Concomitant diminution of the response to beta-adrenergic stimulation, with previously-demonstrated beta receptor downregulation and unaltered postreceptor-mediated activity, suggests that the blunted response to prostacyclin is due to receptor downregulation. Parallel studies of the thoracic aorta indicated that these changes are specific to the pulmonary artery. It is postulated that attenuation of the response of adenylate cyclase to prostacyclin may contribute to the structural changes and hypertension observed in the pulmonary vasculature of the rat with chronic hypoxia.

Differences in prostaglandin metabolism in cultured aortic and pulmonary arterial endothelial cells exposed to acute and chronic hypoxia

In vivo, a marked difference in blood oxygen tension exists between the pulmonary artery and the aorta. Responses of vascular endothelial cells from these vessels to changes in ambient oxygen might be influenced by the oxygen tension to which they are continuously exposed in vivo or by their anatomic site. To explore this hypothesis, we initially studied the production of the cyclooxygenase metabolites prostacyclin and thromboxane in bovine aortic and main pulmonary arterial endothelial cells grown in 21% O2 and exposed to different degrees of acute hypoxia over a wide range of times. We found that short-term hypoxia (3% or 0% O2) rapidly and transiently activates the cyclooxygenase pathway in both cell types, with a more rapid response in bovine aortic endothelial cells. To determine whether culture in an oxygen tension similar to that to which main pulmonary arterial endothelial cells are exposed in vivo alters this response, we evaluated these cyclooxygenase metabolites in bovine aortic and main pulmonary arterial endothelial cells cultured long-term in 3% O2, both at baseline and after exposure to acute anoxia (0% O2). In both cell types, we found a decrease in prostacyclin and thromboxane synthesis at baseline and evidence of an increase in the Vmax of thromboxane synthetase following stimulation with exogenous arachidonic acid. In chronically hypoxic cells exposed to acute anoxia, there were marked differences in enzyme activity compared with that in endothelial cells maintained in 21% O2 with differences depending on the origin of the endothelial cells. In bovine aortic endothelial cells, production of neither cyclooxygenase metabolite increased; in bovine main pulmonary arterial endothelial cells, only thromboxane production increased, suggesting isolated activation of the cyclooxygenase-thromboxane synthetase pathway. These studies demonstrate that acute and chronic hypoxia have profound effects on endothelial cell cyclooxygenase metabolism and that these effects depend on the duration and degree of the hypoxic exposure and the vascular bed from which the endothelial cells are derived.

Effects of cigarette smoking, hypoxia and vasoactive mediators on the production of PGI2 and TXA2 in cultured pulmonary artery endothelial cells

Effects of cigarette smoke extract (CSE) and some vasoactive mediators on the production of PGI2 and TXA2 in normoxic and hypoxic pulmonary artery endothelial cells (PAECs) in culture were studied. The production of PGI2 in PAECs was inhibited by hypoxia or verapamil, but promoted by angiotensin II (A II), noradrenaline (NE) or platelet activating factor (PAF), while that of TXA2 slightly increased except when treated with PAF. The effect of AII, NE, PAF and verapamil, however, was not influenced by hypoxia. CSE inhibited the production of PGI2 in normoxic PAECs but did not further reduce 6-keto-PGF1 alpha in hypoxic PAECs medium. The results suggest that a) the production of PGI2 during hypoxia might be stimulated by vasoactive mediators produced during hypoxia, not by hypoxia directly; b) the production and release of PGI2 were related to intracellular calcium; c) the augmented production of PGI2 might be one of the mechanisms in the pulmonary vasodilating role of PAF; and d) prostaglandin production might be associated with the alteration of hypoxic pulmonary vasoreactivity after cigarette smoking.

Effects of hypoxia and metabolic inhibitors on production of prostacyclin and endothelium-derived relaxing factor by pig aortic endothelial cells

1. The content of adenosine triphosphate (ATP) and basal and bradykinin-stimulated production of prostacyclin and endothelium-derived relaxing factor (EDRF) was measured in primary cultures of porcine aortic endothelial cells under normoxic (14.4% O2) and hypoxic (2.8% O2) conditions, and following treatment with rotenone and 2-deoxy glucose, which inhibit oxidative and glycolytic metabolism, respectively. 2. ATP content and basal and bradykinin-stimulated production of prostacyclin were similar under normoxic and hypoxic conditions. EDRF production, assessed as endothelial guanosine 3':5'-cyclic monophosphate (cyclic GMP) content, was also similar under both conditions. 3. Treatment with rotenone (0.3 microM) had no effect on ATP content or basal or bradykinin-stimulated production of prostacyclin or of EDRF, measured as endothelial cyclic GMP content. Elevation of cyclic GMP content by atriopeptin II was also unaffected. 4. Treatment with 2-deoxy glucose (20 mM) in glucose-free Krebs solution lowered ATP content, reduced bradykinin-stimulated production of prostacyclin and abolished the bradykinin-stimulated elevation of cyclic GMP content. Resting production of prostacyclin was unaffected but basal content of cyclic GMP was lowered in some experiments. Elevation of cyclic GMP content by atriopeptin II was abolished. 5. Combined treatment with rotenone (0.3 microM) and 2-deoxy glucose (20 mM) lowered ATP content more than with 2-deoxy glucose alone. Basal production of prostacyclin rose slightly and bradykinin-stimulated production was powerfully inhibited. Basal content of cyclic GMP was unaffected, but bradykinin-stimulated production was abolished. Elevation of cyclic GMP by atriopeptin II was also abolished. 6. Cascade bioassay experiments using endothelium-denuded rings of rabbit aorta as a detector system confirmed that bradykinin-stimulated production of EDRF was blocked by 2-deoxy glucose, but not by rotenone. 7. These data indicate that porcine aortic endothelial cells in culture operate under mainly glycolytic metabolism and this probably explains why production of prostacyclin and EDRF is unaffected under hypoxic conditions. They also indicate that glycolytic metabolism is required for agonist-stimulated production of prostacyclin and EDRF by these cells.

Hypoxic contraction of cultured pulmonary vascular smooth muscle cells

The cellular events involved in generating the hypoxic pulmonary vasoconstriction response are not clearly understood, in part because of the multitude of factors that alter pulmonary vascular tone. The goal of the present studies was to determine if a cell culture preparation containing vascular smooth muscle (VSM) cells could be made to contract when exposed to a hypoxic atmosphere. Cultures containing only fetal bovine pulmonary artery VSM cells were assessed for contractile responses to hypoxic stimuli by two methods. In the first, tension forces generated by cells grown on a flexible growth surface (polymerized polydimethyl siloxane) were manifested as wrinkles and distortions of the surface under the cells. Wrinkling of the surface was noted to progressively increase with time as the culture medium bathing the cells was made hypoxic (PO2 approximately 25 mmHg). The changes were sometimes reversible upon return to normoxic conditions and appeared to be enhanced in cells already exhibiting evidence of some baseline tone. Repeated passage in culture did not diminish the hypoxic response. Evidence for contractile responses to hypoxia was also obtained from measurements of myosin light chain (MLC) phosphorylation. Conversion of MLC to the phosphorylated species is an early step in the activation of smooth muscle contraction. Lowering the PO2 in the culture medium to 59 mmHg caused a 45% increase in the proportion of MLC in the phosphorylated form as determined by two-dimensional gel electrophoresis. Similarly, cultures preincubated for 4 h with 32P and then exposed to normoxia or hypoxia for a 5-min experimental period showed more than twice as much of the label in MLCs of the hypoxic cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced prostacyclin formation after reoxygenation of anoxic endothelium

Human umbilical vein endothelial cells subjected to 24 h of anoxia followed by reoxygenation released less prostacyclin (PGI2) in response to thrombin, calcium ionophore A23187, or arachidonic acid. This was associated with a substantial increase in stimulated platelet adherence. Increased lactate dehydrogenase and 51Cr release occurred after 1 h of reoxygenation, but the high rate of release did not persist during the subsequent 23 h of reoxygenation. The changes in platelet adherence and PGI2 release partially resolved over 24 h. PGI2 formation from prostaglandin H2 was not reduced, suggesting that cyclooxygenase activity, but not prostacyclin synthase, is affected by reoxygenation. A decrease in arachidonic acid release from cellular lipids also occurred. The reduction in cyclooxygenase activity, but not arachidonic acid release, was prevented by the presence of ibuprofen during reoxygenation. Addition of catalase or superoxide dismutase during reoxygenation increased PGI2 release but did not completely overcome the reduction relative to control cultures. These findings suggest that the increase in platelet adherence during reoxygenation may be mediated in part by a change in cyclooxygenase activity. This is only partly overcome by extracellular oxygen species scavengers but is prevented by the presence of a reversible cyclooxygenase inhibitor during reoxygenation.

Effect of long-term hypoxia on cultured aortic and pulmonary arterial endothelial cells

In a previous study, we found a marked difference in the release of a cytokine, neutrophil chemoattractant activity (NCA), from cultured endothelial cells exposed to acute decreases in ambient oxygen, depending on the vascular bed of origin. In the current study, we used this cytokine to evaluate the effect of long-term exposure to decreased oxygen on endothelial cell function. We found that, in aortic and pulmonary arterial endothelial cells maintained for months in decreased ambient oxygen (10 or 3% oxygen), exposure to acute decreases in ambient oxygen caused a change in the pattern of NCA release; however, the differential response between the two cell types persisted. Aortic endothelial cells release NCA when exposed acutely to a level of oxygen below that in which they have been chronically maintained. In contrast, pulmonary arterial endothelial cells release NCA only when exposed to 0% oxygen acutely, but only if grown chronically in 10% oxygen; otherwise there was no release of NCA. As another indicator of endothelial cell function, we evaluated the effects of acute hypoxic exposure on prostacyclin production by endothelial cells maintained in 21 or 3% oxygen. If grown in 21% oxygen, both cell types decreased prostacyclin production upon exposure to 0% oxygen. However, when grown in 3% oxygen, only aortic endothelial cells decreased prostacyclin production when exposed acutely to 0% oxygen; pulmonary arterial endothelial cell prostacyclin production did not change. This study demonstrating the persistence of a differential pattern of NCA release and the appearance of a differential pattern of prostacyclin production after a long-term decrease in environmental oxygen suggests that the capacity of certain vascular endothelial cells to respond to decreases in oxygen concentration is carried by the cell throughout its existence. Thus, in certain situations, vascular endothelial cells may be important in sensing acute decreases in ambient oxygen.

Decreased arterial wall prostaglandin production in neonatal calves with severe chronic pulmonary hypertension

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.