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

EETs promote hypoxic pulmonary vasoconstriction via constrictor prostanoids

To test the hypothesis that epoxyeicosatrienoic acids (EETs) facilitate pulmonary responses to hypoxia, male wild-type (WT) and soluble-epoxide hydrolase knockout (sEH-KO) mice, and WT mice chronically fed a sEH inhibitor (t-TUCB; 1 mg·kg^-1·day^-1) were used. Right ventricular systolic pressure (RVSP) was recorded under control and hypoxic conditions. The control RVSP was comparable among all groups. However, hypoxia elicited increases in RVSP in all groups with predominance in sEH-KO and t-TUCB-treated mice. 14,15-EEZE (an EET antagonist) attenuated the hypoxia-induced greater elevation of RVSP in sEH-deficient mice, suggesting an EET-mediated increment. Exogenous 5,6-; 8,9-, or 14,15-EET (0.05 ng/g body wt) did not change RVSP in any conditions, but 11,12-EET enhanced RVSP under hypoxia. Isometric tension was recorded from pulmonary arteries isolated from WT and sEH-KO mice, vessels that behaved identically in their responsiveness to vasoactive agents and vessel stretch. Hypoxic pulmonary vasoconstriction (HPV, expressed as increases in hypoxic force) was significantly greater in vessels of sEH-KO than WT vessels; the enhanced component was inhibited by EEZE. Treatment of WT vessels with 11,12-EET enhanced HPV to the same level as sEH-KO vessels, confirming EETs as primary players. Inhibition of cyclooxygenases (COXs) significantly enhanced HPV in WT vessels, but attenuated HPV in sEH-KO vessels. Blocking/inhibiting COX-1, prostaglandin H₂ (PGH₂)/thromboxane A₂ (TXA₂) receptors and TXA synthase prevented the enhanced HPV in sEH-KO vessels but had no effects on WT vessels. In conclusion, an EET-dependent alteration in PG metabolism that favors the action of vasoconstrictor PGH₂ and TXA₂ potentiates HPV and hypoxia-induced elevation of RVSP in sEH-deficient mice.

Arteriolar oxygen reactivity: where is the sensor and what is the mechanism of action?

Arterioles in the peripheral microcirculation are exquisitely sensitive to changes in PO2 in their environment: increases in PO2 cause vasoconstriction while decreases in PO2 result in vasodilatation. However, the cell type that senses O2 (the O2 sensor) and the signalling pathway that couples changes in PO2 to changes in arteriolar tone (the mechanism of action) remain unclear. Many (but not all) ex vivo studies of isolated cannulated resistance arteries and large, first-order arterioles support the hypothesis that these vessels are intrinsically sensitive to PO2 with the smooth muscle, endothelial cells, or red blood cells serving as the O2 sensor. However, in situ studies testing these hypotheses in downstream arterioles have failed to find evidence of intrinsic O2 sensitivity, and instead have supported the idea that extravascular cells sense O2 . Similarly, ex vivo studies of isolated, cannulated resistance arteries and large first-order arterioles support the hypotheses that O2 -dependent inhibition of production of vasodilator cyclooxygenase products or O2 -dependent destruction of nitric oxide mediates O2 reactivity of these upstream vessels. In contrast, most in vivo studies of downstream arterioles have disproved these hypotheses and instead have provided evidence supporting the idea that O2 -dependent production of vasoconstrictors mediates arteriolar O2 reactivity, with significant regional heterogeneity in the specific vasoconstrictor involved. Oxygen-induced vasoconstriction may serve as a protective mechanism to reduce the oxidative burden to which a tissue is exposed, a process that is superimposed on top of the local mechanisms which regulate tissue blood flow to meet a tissue's metabolic demand.

Hypoxic pulmonary vasoconstriction

It has been known for more than 60 years, and suspected for over 100, that alveolar hypoxia causes pulmonary vasoconstriction by means of mechanisms local to the lung. For the last 20 years, it has been clear that the essential sensor, transduction, and effector mechanisms responsible for hypoxic pulmonary vasoconstriction (HPV) reside in the pulmonary arterial smooth muscle cell. The main focus of this review is the cellular and molecular work performed to clarify these intrinsic mechanisms and to determine how they are facilitated and inhibited by the extrinsic influences of other cells. Because the interaction of intrinsic and extrinsic mechanisms is likely to shape expression of HPV in vivo, we relate results obtained in cells to HPV in more intact preparations, such as intact and isolated lungs and isolated pulmonary vessels. Finally, we evaluate evidence regarding the contribution of HPV to the physiological and pathophysiological processes involved in the transition from fetal to neonatal life, pulmonary gas exchange, high-altitude pulmonary edema, and pulmonary hypertension. Although understanding of HPV has advanced significantly, major areas of ignorance and uncertainty await resolution.

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.

Identification of the phospholipase A(2) isoforms that contribute to arachidonic acid release in hypoxic endothelial cells: limits of phospholipase A(2) inhibitors

Changes in endothelium functions during ischemia are thought to be of importance in numerous pathological conditions, with, for instance, an increase in the release of inflammatory mediators like prostaglandins. Here, we showed that hypoxia increases phospholipase A(2) (PLA(2)) activity in human umbilical vein endothelial cells. Both basal PLA(2) activity and PG synthesis are sensitive to BEL and AACOCF3, respectively, inhibitors of calcium-independent PLA(2) (iPLA(2)) and cytosolic PLA(2) (cPLA(2)), while OPC, an inhibitor of soluble PLA(2) (sPLA(2)) only inhibited the hypoxia-induced AA release and PGF(2alpha) synthesis. Hypoxia does not alter expression of iPLA(2), sPLA(2) and cPLA(2) and cycloheximide did not inhibit PLA(2) activation, indicating that hypoxia-induced increase in PLA(2) activity is due to activation rather than induction. However, mRNA levels for sPLA(2) displayed a 2-fold increase after 2 hr incubation under hypoxia. BAPTA, an intracellular calcium chelator, partially inhibited the AA release in normoxia and in hypoxia. Direct assays of specific PLA(2) activity showed an increase in sPLA(2) activity but not in cPLA(2) activity after 2hr hypoxia. Taken together, these results indicate that the hypoxia-induced increase in PLA(2) activity is mostly due to the activation of sPLA(2).

New and experimental therapies for pulmonary hypertension

Advances in the understanding of the molecular and cellular pathogeneses of PPH have led clinicians beyond simple pulmonary vasodilation as the only treatment for PPH and to a realization that what were previously believed to be irreversible vascular lesions may, in fact, be reversible. The development of agents that target the known endothelial and nonendothelial defects in patients with PPH is well underway. Clinicians are witnessing an exciting new era for physicians and patients dealing with this disease.

PGF(2alpha), a prostanoid released by endothelial cells activated by hypoxia, is a chemoattractant candidate for neutrophil recruitment

Despite increasing evidence supporting the involvement of neutrophils in ischemic and postischemic damages, the mechanisms underlying the early recruitment of these cells are not completely understood. In this report, the effects of conditioned media from hypoxic endothelial cells on neutrophil chemotaxis were investigated by biochemical and morphological studies. We showed that conditioned media collected from several endothelial cell origins submitted to hypoxia as well as ischemic rat liver perfusion liquids have a chemotactic activity for neutrophils. The role of various chemoattractant molecules like HETEs, platelet-activating factor, and cytokines such as interleukin-8 and interleukin-1 was examined in the same model. Chemotactic peptide contribution was ruled out as boiled conditioned media still trigger chemotaxis. However, cell treatment with cyclooxygenase inhibitors, neutralization of PGF(2alpha) biological activity with polyclonal antibodies, and the neutrophil preincubation with a specific PGF(2alpha) antagonist, all dramatically inhibited neutrophil chemotaxis. A strong chemoattractant effect of pure exogenous PGF(2alpha) or of a synthetic analog was also observed. The major effect of PGF(2alpha) on neutrophil chemotaxis was confirmed ex vivo in a rat liver perfusion ischemic model. These results suggest that PGF(2alpha), a prostanoid abundantly released by the endothelium of hypoxic or ischemic tissues, is a chemoattractant molecule that might be involved in the early recruitment of neutrophils in ischemic organs.

Endothelial cell responses to hypoxia: initiation of a cascade of cellular interactions

The origin of several vascular pathologies involves sudden or recurrent oxygen deficiency. In this review, we examine what the biochemical and molecular responses of the endothelial cells to the lack of oxygen are and how these responses may account for the features observed in pathological situations, mainly by modifications of cell-cell interactions. Two major responses of the endothelial cells have been observed depending on the degree and duration of the oxygen deficiency. Firstly, acute hypoxia rapidly activates the endothelial cells to release inflammatory mediators and growth factors. These inflammatory mediators are able to recruit and promote the adherence of neutrophils to the endothelium where they become activated. The synthesis of platelet-activating factor plays a key role in this adherence process. Secondly, longer periods of hypoxia increase the expression of specific genes such as those encoding some cytokines as well as for the growth factors platelet-derived growth factor and vascular endothelial growth factor. The transcriptional induction of these genes is mediated through the activation of several transcription factors, the most important one being hypoxia inducible factor-1. The link between our knowledge of the signalling cascade of the cellular and molecular events initiated by hypoxia and their involvement in several vascular pathological situations, varicose veins, tumor angiogenesis and pulmonary hypertension is discussed briefly.

Hypoxic pulmonary vasoconstriction is impaired in rats with nitrofen-induced congenital diaphragmatic hernia

BACKGROUND

Pulmonary hypertension and persistent fetal circulation contribute to the high mortality rate associated with congenital diaphragmatic hernia (CDH). Morphological alterations of the pulmonary vasculature in infants with CDH are thought to contribute to exaggerated vasoconstrictor responses to normal vasoconstrictor stimuli. In the pulmonary circulation, hypoxia is a potent vasoconstrictor. Under pathological conditions, hypoxia-induced vasoconstriction may contribute to the development of pulmonary hypertension.

METHODS

The authors have used the nitrofen-induced model of congenital diaphragmatic hernia in rats to investigate the magnitude of the hypoxic vasoconstrictor response. Congenital diaphragmatic hernias were induced in fetal rats by feeding nitrofen (2,4-dichlorophenyl-p-nitrophenyl ether) to pregnant Sprague-Dawley rats at midgestation. Hypoxia-induced vasoconstriction was measured in isolated, perfused third-generation pulmonary arterioles from normal rats and from rats with nitrofen-induced CDH.

RESULTS

The hypoxic vasoconstrictor response was significantly blunted in the pulmonary arterioles of fetal rats with nitrofen-induced (2% +/- 1% vasoconstriction), as compared with the responses observed in normal fetal rats (15% +/- 3% vasoconstriction, P = .004).

CONCLUSION

Blunting of the hypoxic pulmonary vasoconstrictor response may contribute to ventilation-perfusion mismatching in infants with CDH.

Prostanoid production in the umbilicoplacental arterial tree relative to impaired glucose tolerance

The purpose of this study was to investigate prostanoid synthesis in different segments of the umbilicoplacental vascular tree and its relationship to impaired maternal glucose tolerance. Segments from the umbilical artery and vein, allantochorionic artery branches, and the cotyledon artery from 21 women with diabetes or impaired glucose tolerance and 10 healthy women were studied. Production of prostacyclin (PGI2) and thromboxane (TxA2) metabolites was determined. The Mann-Whitney U test, Wilcoxon signed-ranks matched-pairs test, Kruskal-Wallis test, analysis of variance, and simple linear regression analysis were used. A two-tailed P value of < 0.05 was considered statistically significant. From the umbilical artery distal to the cotyledon artery, the PGI2 synthesis decreased and the TxA2 synthesis increased gradually towards the periphery in normal pregnancy. The PGI2/TxA2 ratio was more than 200 times higher in the umbilical artery than in the cotyledon artery. The TxA2 production tended in general to be higher in the diabetic group than in the control group, resulting in significantly lower PGI2/TxA2 ratios in some vessels. The prostanoid production was not significantly correlated to maternal HbA1c or cord C-peptide concentrations. The balance between vascular prostacyclin and thromboxane synthesis in the umbilicoplacental arterial tree changed gradually towards the periphery: the more peripheral, the lower the prostacyclin and the higher the thromboxane production. The physiological role of this phenomenon is unknown, but may be of importance for the equilibration of vascular tone between arteries of different calibers. The altered prostanoid balance found in diabetic pregnancy was not directly attributable to the degree of maternal glycemic control, but may reflect increased free radical activity and peroxide production in diabetes.

Association between a low umbilical artery pulsatility index and fetal distress in labor in very prolonged pregnancies

OBJECTIVE

To investigate the association between fetal, umbilical and uterine circulatory changes and adverse perinatal findings in very prolonged pregnancies.

STUDY DESIGN

44 women proceeding to 43 completed weeks of gestation with the intention of a trial of vaginal delivery were studied prospectively with ultrasound Doppler velocimetry. An intensified fetal surveillance was routinely commenced at 42 weeks and only uncomplicated pregnancies were allowed to proceed. The endpoint perinatal measures were oligohydramnios, fetal meconium release, fetal distress in labor and birth asphyxia. Flow variables in different groups were compared with the Mann-Whitney U test, Student's unpaired t-test, Wilcoxon signed-rank matched-pairs test, Fisher's exact test and contingency table analysis, and a two-tailed P value <0.05 was considered statistically significant.

RESULTS

The umbilical artery pulsatility index was significantly lower in cases of fetal meconium release (n=12) and fetal distress (n=7). The umbilical venous flow velocity was significantly lower in cases of meconium, and the fetal aortic volume flow significantly higher in cases of fetal distress. No significant flow changes were found in connection with oligohydramnios (n=5) and birth asphyxia (n=2). Uterine flow was not significantly affected in any group.

CONCLUSIONS

In very prolonged pregnancies, fetal distress in labor was not associated with an increased placental vascular resistance. In contrast to previous reports, the umbilical artery pulsatility index was low in cases of fetal distress and meconium release. The etiology is unknown, but a subclinical fetal hypoxia might have triggered a vasodilation of placental vessels. Vasodilation at an unchanged volume flow could also explain the decrease of umbilical venous flow velocity. The increased aortic volume flow indicates an increase of cardiac output in fetuses later developing distress in labor.

Flow-induced modulation of the permeability of endothelial cells cultured on microcarrier beads

The maintenance of endothelial barrier function is important in the regulation of fluid and solute balance between the vascular space and the surrounding tissue. Since fluid flow across endothelial cells stimulates a wide variety of endothelial responses, the effect of shear stress on barrier function was investigated. Bovine pulmonary artery endothelial cells were cultured on permeable microcarrier beads, placed in a chromatography column, and perfused. Indicator-dilution techniques were used to estimate the permeability of the cell-covered beads to low molecular weight tracers (sodium fluorescein-NaFlsc; cyanocobalamin-B12) as a function of flow rate through the column. Permeability values for both tracers were significantly increased (9.3 +/- 0.6 to 19.3 +/- 1.7 for NaFlsc; 8.2 +/- 0.5 to 20.4 +/- 3.1 for B12; mean+/-SEM, x 10(-5) cm/s, P < .05) when the flow rate was increased from 0.9 ml/min to 3.2 ml/min (corresponding to average shear stresses of 4.7 and 16.8 dynes/cm2). The permeability increase occurred within minutes of the flow increase, and was reversed by decreasing the flow rate to 0.9 ml/min. In the presence of cytochalasin D, the flow-induced permeability increase was not reversible. Neither inhibition of nitric oxide synthase (with NG-monomethyl-L-arginine) nor inhibition of cyclooxygenase (with indomethacin) was capable of blocking the flow-induced permeability increase. These results indicate that the rapid modulation of endothelial barrier by flow in vitro is probably not due to prostacyclin or nitric oxide.

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.

Oxygen modulates production of bFGF and TGF-beta by retinal cells in vitro

Vasoproliferative retinopathies result from retinal capillary non-perfusion and consequent inner retinal hypoxia. However, it is not known whether oxygen mediates vasoproliferation directly (at the nuclear level) or indirectly by regulating the production of growth factors. We have investigated the effect of oxygen on the production of basic fibroblast growth factor and transforming-growth-factor-beta by a variety of retinal cell types in culture. Confluent cultures were maintained for 48 hr under varying oxygen tensions ranging from 135 to 18 mmHg. A reduction in basic fibroblast growth factor levels was observed in the cell lysates and extracellular matrix from retinal microvascular endothelial cell, retinal microvascular pericyte and retinal pigment epithelial cell cultures when the oxygen tension of the medium was reduced from 135 to 18 mmHg. Levels of basic fibroblast growth factor in conditioned media from microvascular endothelial and retinal pigment epithelial cell cultures also decreased when the oxygen tension of the medium was reduced from 135 to 18 mmHg. Total transforming-growth-factor-beta (and specifically isoforms 1 and 2) in the conditioned media from all three cell types was similarly modulated by oxygen i.e. it decreased as the oxygen tension of the medium was reduced from 135 to 18 mmHg. In contrast, the steady state messenger RNA levels for both basic fibroblast growth factor and transforming-growth-factor-beta 1 genes in RPE cells increased significantly when the oxygen tension of the medium was reduced from 135 to 18 mmHg. These results support the putative role of oxygen in influencing the balance of growth factors during the development of preretinal new vessels.

Effects of 3,4-dihydroxyacetophenone (3,4-DHAP) on hypoxic pulmonary and systemic vascular response in dogs

The effects of 3,4-DHAP on hypoxic pulmonary and systemic vascular responses were studied in anaesthetized dogs. The percentage change in pulmonary vascular resistance (delta PVR %) and that in systemic vascular resistance (delta SVR %) induced by 5 min hypoxia decreased significantly. 3,4-DHAP in doses of 1 mg/kg, 3 mg/kg, and 10 mg/kg i.v. caused a decrease in delta PVR% from the control value of 47.27 +/- 22.27% to 24.62 +/- 21.76%, 18.15 +/- 18.73%, and 24.10 +/- 19.76% respectively, and a decrease in delta SVR % from the control value of 12.91 +/- 7.39 % to -0.34 +/- 12.70%, -2.11 +/- 12.76%, and -2.37 +/- 15.52 % respectively. The results showed that 3,4-DHAP could decrease the hypoxic responses of pulmonary and systemic blood vessels. But it did not change delta PVR % or delta SVR % in dose of 30 mg/kg, neither did it influence the heart rate, cardiac output or cerebral blood flow during hypoxia in all the doses used.

Effects of 3,4-dihydroxyacetophenone on hypoxic vasoconstriction in isolated pulmonary and basilar arterial rings

The effects of 3,4-DHAP on hypoxic vasoconstriction response in pulmonary (PA) and basilar arterial (BA) rings of rabbits and their mechanism were compared in vitro. 3,4-DHAP in different concentration (2.64 x 10(-4), 7.92 x 10(-4), 2.376 x 10(-3) mol/L) decreased the basal tone of PA rings by 32.39 +/- 9.4 mg, 68.96 +/- 26.54 mg and 145.60 +/- 58.07 mg respectively, while the tension of the BA rings was decreased by 13.80 +/- 5.08 mg, 17.18 +/- 3.36 mg and 25.00 +/- 4.02 mg respectively. In PA rings it also decreased the percentage increase in tension induced by hypoxia (TIH%) from the control value 48.82 +/- 5.75% to 10.02 +/- 3.62%, 2.14 +/- 0.96%, and 0.00% respectively, while in BA rings from 27.27 +/- 5.78% to 11.23 +/- 2.71%, 7.49 +/- 1.62%, and 1.45 +/- 1.13% respectively. The effects of 3, 4-DHAP on TIH% were partially blocked by indomethacin 10 M and L-NAME 10 M. The results showed that 3, 4-DHAP can decrease the hypoxic pulmonary and basilar vasoconstriction in vitro, which can be partially inhibited by cyclooxygenase inhibitor and NO/EDRF inhibitor.

17 beta-Estradiol inhibits flow- and acute hypoxia-induced prostacyclin release from perfused endocardial endothelial cells

BACKGROUND

Because of the marked difference in the incidence and severity of cardiovascular diseases between men and premenopausal women, several groups have studied the effect of sex steroids, particularly estrogen, on vascular endothelial prostacyclin (PGI2) release. No previous studies have addressed the effect of estrogen on endocardial endothelial cells (EECs), which are involved in the modulation of the myocardium and potentially in downstream pulmonary and systemic vascular tone. Furthermore, all previous studies of estrogen effects on cultured endothelial cell function have used cells grown under standard static cell culture conditions, thereby ignoring the contribution of flow, the ubiquitous environmental endothelial stimulus.

METHODS AND RESULTS

The effect of 17 beta-estradiol pretreatment (100 ng/mL, 72 hours) on cultured sheep EEC PGI2 release in response to multiple physiologically relevant stimuli was studied. EECs were grown in six-well plates (static conditions) or on microcarrier beads and perfused at a constant flow with normoxic (PO2 = 150 mm Hg, PCO2 = 35 mm Hg) or hypoxic (PO2 = 35 mm Hg, PCO2 = 35 mm Hg) Krebs solution. The stable metabolite of PGI2, 6-keto-PGF1 alpha, was determined in samples from both static and perfusion experiments by direct radioimmunoassay. 17 beta-Estradiol pretreatment did not alter basal or stimulated (arachidonic acid, 1 mumol/L, 10 mumol/L; A23187, 10 mumol/L; and bradykinin, 1 mumol/L) PGI2 release in static conditions. Untreated and acutely treated (100 ng/mL added to perfusate) EECs responded to flow with a time-dependent increase in PGI2 release that plateaued between 60 and 100 minutes. In contrast, 17 beta-estradiol-pretreated, perfused EECs did not increase PGI2 release over time. During perfusion, acute hypoxia increased PGI2 release: 140 +/- 65 (normoxia) to 296 +/- 113 pg (hypoxia) 6-keto-PGF1 alpha/mg per minute. 17 beta-Estradiol inhibited hypoxia-induced PGI2 release: 296 +/- 113 pg (untreated EECs, hypoxia) versus 159 +/- 60 pg (17 beta-estradiol pretreated, hypoxia) 6-keto-PGF1 alpha/mg per minute.

CONCLUSIONS

This study demonstrates for the first time an inhibitory effect of 17 beta-estradiol on flow- and acute hypoxia-induced increase in PGI2 release from perfused EECs in the absence of any effect on pharmacologically stimulated PGI2 release from static cultures. These effects of 17 beta-estradiol may explain in part the well-recognized gender and estrogen effects in cardiovascular diseases and highlight the importance of flow in studies of endothelial cell function.

Vasoconstrictor and vasodilator effects of hypoxia

Hypoxia has marked effects on artery calibre, which reflects important physiological control mechanisms that are altered in disease states. Hypoxia modifies the release of mediators, especially from the endothelium, and influences smooth muscle membrane potential and Ca2+ regulation. In this review, Roger Wadsworth evaluates the vasoconstrictor and vasodilator effects of hypoxia studied in vitro. In the future, drugs developed to act on the mediators or smooth muscle may be beneficial in the therapy of, for example, pulmonary hypertension or coronary vasospasm.

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.