Multimodality Imaging in the Detection of Ischemic Heart Disease in Women

Women with coronary artery disease tend to have a worse short and long-term prognosis relative to men and the incidence of atherosclerotic cardiovascular disease is increasing. Women are less likely to present with classic anginal symptoms when compared with men and more likely to be misdiagnosed. Several non-invasive imaging modalities are available for diagnosing ischemic heart disease in women and many of these modalities can also assist with prognostication and help to guide management. Selection of the optimal imaging modality to evaluate women with possible ischemic heart disease is a scenario which clinicians often encounter. Earlier modalities such as exercise treadmill testing demonstrate significant performance variation in men and women, while newer modalities such as coronary CT angiography, myocardial perfusion imaging and cardiac magnetic resonance imaging are highly specific and sensitive for the detection of ischemia and coronary artery disease with greater parity between sexes. Individual factors, availability, diagnostic performance, and female-specific considerations such as pregnancy status may influence the decision to select one modality over another. Emerging techniques such as strain rate imaging, CT-myocardial perfusion imaging and cardiac magnetic resonance imaging present additional options for diagnosing ischemia and coronary microvascular dysfunction.

New Strategies for Lowering Low Density Lipoprotein Cholesterol for Cardiovascular Disease Prevention

Purpose of review

The primary and secondary prevention of atherosclerotic cardiovascular disease (ASCVD) relies on optimizing cardiovascular health and appropriate pharmacotherapy, a mainstay of which is low-density lipoprotein-cholesterol (LDL-C) lowering. Typically, statin therapy remains the first line approach. Advances in technology and understanding of lipid metabolism have facilitated the development of several novel therapeutic targets and medications within the last decade. This review focuses on medications recently approved by the U.S. Food and Drug Administration (FDA) for the reduction of LDL-C and ASCVD risk, as well as new therapies in the pipeline.

Recent findings

Novel lipid therapies aim to lower risk of ASCVD by targeting reduction of atherogenic compounds, such as LDL, lipoprotein(a) (Lp(a)), and triglyceride-rich lipoproteins. Evolocumab and alirocumab, monoclonal antibody proprotein convertase subtilisin-kexin type 9 (PCSK9) inhibitors which lower LDL-C by approximately 60%, have emerged as important therapies for use in patients with ASCVD as well as familial hypercholesterolemia (FH). Bempedoic acid, an ATP citrate lyase inhibitor, is an oral medication recently approved that can lower LDL-C by approximately 18% alone and 38% when combined with ezetimibe. Inclisiran, a small-interfering RNA (siRNA) molecule which inhibits the translation of PCSK9, is the most recently FDA-approved LDL-C lowering medication, and can reduce LDL-C by approximately 50% with twice yearly subcutaneous dosing. The cardiovascular outcome trials for bempedoic acid and inclisiran are still on-going. Evinacumab, a monoclonal antibody which targets angiopoietin-like protein 3 (ANGPTL3), has been approved for use in patients with homozygous FH. SiRNAs and anti-sense oligonucleotides (ASO) facilitating selective inhibition of the production of targeted proteins including Lp(a) and ANGLPTL3 are active areas of clinical investigation.

Summary

Recently several novel LDL-C lowering medications have been approved. New therapeutic targets have been identified and present additional means of lowering LDL-C and other atherogenic compounds for patients who remain at high ASCVD risk.

Sitaxsentan: an endothelin-A receptor antagonist for the treatment of pulmonary arterial hypertension

Endothelin (ET-1) is a potent vasoconstrictor and smooth muscle mitogen that mediates its effects through activation of ET-A and ET-B receptors. Pulmonary arterial hypertension (PAH) encompasses a heterogeneous group of disorders characterised by inappropriate overactivation of the ET system. There is clear evidence that strategies that block both ET receptors are associated with clinical improvement in PAH. However, there are theoretical physiological advantages to treatments that specifically inhibit only the ET-A receptor. Sitaxsentan is an orally active selective ET-A receptor antagonist that in recent clinical trials has demonstrated improvements in exercise capacity, functional class and haemodynamics in PAH patients with modified New York Heart Association class II, III and IV symptoms.

Lung transplantation for pulmonary hypertension

Although lung transplantation is a viable option for patients with end-stage pulmonary hypertension, it is associated with numerous problems including infection, rejection, and limited long-term survival. Because of these limitations, transplantation should only be considered for patients who are failing maximal medical therapy. Treatment options for patients with pulmonary hypertension that may serve to prolong or obviate the need for transplantation include anticoagulation with warfarin, diuretics, and vasodilators such as calcium channel blockers or continuous intravenous epoprostenol (prostacyclin). The response to medical therapy should be assessed at regular intervals by evaluating exercise tolerance and hemodynamic parameters. Because waiting periods for transplantation now exceed 1.5 to 2 years in the United States, and the response to medications is unpredictable, referral for transplantation should occur when patients become symptomatic. Those who are responding well to medical therapy should be removed from the active transplant waiting list, whereas those who fail therapy should go on to transplant. Utilizing medical therapy and transplantation as complementary treatments will achieve the best potential to improve quality of life and prolong survival.

Increased levels of prostaglandin D(2) suggest macrophage activation in patients with primary pulmonary hypertension

STUDY OBJECTIVE

TXA(2) (thromboxane A(2)) is a lipid mediator believed to be produced primarily by platelets in normal subjects, although macrophages are capable of synthesis. There is increased production of TXA(2) in patients with primary pulmonary hypertension (PPH), which may reflect augmented production by macrophages. The objective of this study was to determine if macrophages are activated in PPH and whether they contribute to the increased production of TXA(2).

STUDY TYPE

Case control.

SETTING

University hospital.

METHODS

We measured the urinary metabolites of three mediators that predominantly derive from different cell types in vivo: (1) TX-M (platelets and macrophages), a TXA(2) metabolite; (2) prostaglandin D(2) (PGD(2)) metabolite (PGD-M); and (3) N-methylhistamine (mast cells), a histamine metabolite, in 12 patients with PPH and 11 normal subjects.

RESULTS

The mean (+/- SEM) excretion of both TX-M and PGD-M at baseline was increased in PPH patients, compared to normal subjects (460 +/- 50 pg/mg creatinine vs 236 +/- 16 pg/mg creatinine [p = 0.0006], and 1,390 +/- 221 pg/mg creatinine vs 637 +/- 65 pg/mg creatinine [p = 0.005], respectively). N-methylhistamine excretion was not increased compared to normal subjects. There was a poor correlation between excretion of TX-M and PGD-M (r = 0.36) and between excretion of PGD-M and methylhistamine (r = 0.09) in individual patients.

CONCLUSION

In patients with PPH, increased levels of PGD-M, without increased synthesis of N-methylhistamine, suggest that macrophages are activated. The lack of correlation between urinary metabolite levels of TXA(2) and PGD(2) implies that macrophages do not contribute substantially to elevated TXA(2) production in patients with PPH. They may, however, have a role in the pathogenesis and/or maintenance of PPH, which warrants further investigation.

Primary pulmonary hypertension is not associated with scleroderma-like changes in nailfold capillaries

STUDY OBJECTIVES

To determine whether primary pulmonary hypertension (PPH) is associated with scleroderma-like changes in nailfold capillaries.

DESIGN

Blinded, prospective, case-control study.

SETTING

University medical centers in Baltimore, MD.

PATIENTS

Thirty-seven patients with PPH, 15 patients with scleroderma, and 13 healthy control subjects.

MEASUREMENTS

Subjects underwent nailfold capillary videomicroscopy of the fourth digits of both hands. Capillary images were evaluated by two blinded, trained graders according to standardized criteria for the presence of scleroderma nailfold changes.

RESULTS

The prevalence of scleroderma-associated nailfold changes in patients with PPH (1 of 37 patients) was dramatically lower than that in patients with scleroderma (9 of 15 patients; p < 0.0001). The distribution of nailfold grades for the PPH patients was indistinguishable from that of the healthy control subjects.

CONCLUSION

PPH is not associated with scleroderma-like vasculopathy of nailfold capillaries.

Liver transplantation in patients with severe portopulmonary hypertension treated with preoperative chronic intravenous epoprostenol

Portopulmonary hypertension (PPHTN) is no longer an absolute contraindication to orthotopic liver transplantation (OLT). The pre-OLT management of patients with PPHTN requires early diagnosis and chronic therapy with intravenous epoprostenol to decrease pulmonary vascular resistance (PVR). Close follow-up is necessary to reassess pulmonary artery pressures (PAPs) and evaluate right ventricular (RV) function. This assists in the optimal timing of OLT. Successful management also necessitates reassessment of pulmonary artery hemodynamics just before OLT, with clearly defined parameters used to determine whether to proceed. Even with the intraoperative and postoperative availability of potent pulmonary vasodilators, clinical management may be suboptimal in reducing PAP. Adequate reduction in PVR and improvement in RV function in response to chronic epoprostenol therapy may facilitate successful OLT. We present a case report and review the limited experience with this treatment.

Lung transplantation and systemic sclerosis

We performed lung transplantation in nine patients with Scleroderma related lung disease. Patient characteristics included: 7 (78%) females, 6 (67%) with limited and 3 (33%) with diffuse Scleroderma. Pulmonary fibrosis was present in 7 (78%) and pulmonary hypertension in 4 (44%). All patients were carefully screened by the Johns Hopkins and University of Maryland Scleroderma Center and only referred for transplantation when concomitant renal insufficiency (creatinine clearance < or = 50 ml/min), aspiration, and skin brakdown were excluded. When compared to a similar group of transplant patients with nonscleroderma lung disease (primary pulmonary fibrosis), there was no significant difference in post-transplant survival at four years (76.2 +/- 0.15% vs. 69.2% +/- 0.12%), mean annual incidence rate for acute rejection (0.14 +/- 0.14 vs. 0.47 +/- 0.13) and infection (viral 0.17 +/- 0.17 vs. 0.29 +/- 0.11) (bacterial 0.17 +/- 0.17 vs. 1.4 +/- 0.4) (fungal 0.99 +/- 0.69 vs. 0.36 +/- 0.16) or serum creatinine (1.55 +/- 0.34 mg/dl vs. 1.15 +/- 0.09 mg/dl). We conclude that lung transplantation is viable option for carefully selected patients with scleroderma related lung disease.

Recreational use of aminorex and pulmonary hypertension

Pulmonary hypertension has been associated with ingestion of the appetite suppressant aminorex. A similar compound, 4-methyl-aminorex (street names, "U-4-E-uh" [pronounced euphoria] or "ice"), is a "designer" drug with central stimulant activity. This drug was discovered on the property of three individuals with diagnoses of pulmonary hypertension. The association between "recreational" aminorex manufacture and ingestion and the development of pulmonary hypertension is described.

Epoprostenol for treatment of pulmonary hypertension in patients with systemic lupus erythematosus

OBJECTIVE

Pulmonary hypertension with pathological changes similar to those observed in primary pulmonary hypertension occurs in patients with systemic lupus erythematosus (SLE). The efficacy of chronic epoprostenol therapy in SLE has not been well described. The objective of this paper is to describe our experience with long-term epoprostenol therapy in patients with pulmonary hypertension associated with SLE.

DESIGN

Case series of six patients with SLE and associated pulmonary hypertension receiving chronic treatment with epoprostenol.

RESULTS

All 6 patients had severe pulmonary hypertension. Mean pulmonary artery pressure (mPAP) was 57 +/- 9 mm Hg (mean +/- SD), and pulmonary vascular resistance was 14 +/- 7 units before beginning therapy with epoprostenol. In 4 patients who underwent repeat hemodynamic evaluation (9 to 16 months after starting epoprostenol), mean pulmonary artery pressure decreased by 38 +/- 21% and pulmonary vascular resistance by 58 +/- 12%. Clinically, all patients improved from New York Heart Association class III or IV to class I or II. Doses of epoprostenol ranged from 4 to 46 ng/kg/min, and the longest duration of therapy has been 2.5 years. Side effects from epoprostenol have not differed from those seen in patients with primary pulmonary hypertension, and except for one patient, there has been no exacerbation of SLE.

CONCLUSION

Epoprostenol was effective for the treatment of pulmonary hypertension in this small group of patients with SLE. Further evaluation of epoprostenol therapy for patients with SLE and other diseases associated with pulmonary hypertension is warranted.

Continuous intravenous epoprostenol therapy for pulmonary hypertension in Gaucher's disease

Gaucher's disease is a rare disorder characterized by a deficiency of lysosomal beta-glucosidase. Pulmonary hypertension, the etiology of which is unclear, has been reported to occur in association with Gaucher's disease. We report the use of continuous intravenous epoprostenol (prostacyclin), which has been used to treat other forms of pulmonary hypertension, in a patient with pulmonary hypertension associated with Gaucher's disease. Although its mechanism of action remains unknown, epoprostenol may be an effective form of therapy for chronic pulmonary hypertension due to a variety of conditions, one of which is Gaucher's disease.

Anastomotic pulmonary hypertension after lung transplantation for primary pulmonary hypertension: report of surgical correction

This report describes a patient who developed pulmonary hypertension 6 years after lung transplantation for primary pulmonary hypertension (PPH). Evaluation with right heart catheterization followed by pulmonary angiography, however, demonstrated that the pulmonary hypertension was secondary to an anastomotic narrowing of the pulmonary artery, rather than a recurrence of her PPH. Vascular complications of lung transplantation should be considered in patients who experience exertional dyspnea after lung transplantation. The suggestion of pulmonary hypertension on echocardiography should prompt further evaluation, including meticulous hemodynamic measurements.

Induction of heme oxygenase-1 with hemoglobin depresses vasoreactivity in rat aorta

Septic shock induced by lipopolysaccharide (LPS) produces systemic hypotension and decreased responsiveness to vasoconstrictors. Recently, intravenous injection of hemoglobin (HGB) into rats was found to be protective from a subsequent lethal dose of LPS and was correlated with induction of the enzyme heme oxygenase-1 (HO-1). To determine whether the HGB modulated the vasomotor tone of systemic arteries, we evaluated the effect of in vivo treatment with HGB and LPS on vasoconstrictor responses to phenylephrine (PE) in the isolated rat aorta. Rats (n = 4, for each group) were injected intravenously with rat HGB (200 mg/kg i.v.) or normal saline control (CON) 16 h before sacrifice, and/or LPS (20 mg/kg) or CON 4 h before sacrifice. The descending aorta was dissected into rings and suspended in a modified Krebs solution where vasoconstrictor responses were determined to KCl (60 mM) and PE (10(-8) to 10(-5) M). LPS, but not HGB, inhibited the vasoconstrictor response to KCl. LPS, HGB, and HGB+LPS inhibited the maximal vasoconstrictor response to PE (PEmax). Induction of HO-1 RNA in the aorta by HGB and by LPS was demonstrated by Northern blot analysis. To determine if induction of HO-1 was related to the effect of LPS or HGB on vascular reactivity, vessels were treated with the HO-1 inhibitor, SnPP9 (30 microM). PEmax in SnPP9+HGB vessels was not different from control, whereas SnPP9+LPS vessels had a marked decrease in PEmax. We conclude that induction of HO-1 does not protect the rat aorta from the vasodepressor effects of LPS in vitro. Our results demonstrate, however, that the induction of HO-1 causes vasodepression, possibly via increased production of carbon monoxide.

Dysfunctional voltage-gated K+ channels in pulmonary artery smooth muscle cells of patients with primary pulmonary hypertension

BACKGROUND

Primary pulmonary hypertension (PPH) is a rare disease of unknown cause. Although PPH and secondary pulmonary hypertension (SPH) share many clinical and pathological characteristics, their origins may be disparate. In pulmonary artery smooth muscle cells (PASMCs), the activity of voltage-gated K+ (KV) channels governs membrane potential (Em) and regulates cytosolic free Ca2+ concentration ([Ca2+]cyt). A rise in [Ca2+]cyt is a trigger of vasoconstriction and a stimulus of smooth muscle proliferation.

METHODS AND RESULTS

Fluorescence microscopy and patch clamp techniques were used to measure [Ca2+]cyt, Em, and KV currents in PASMCs. Mean pulmonary arterial pressures were comparable (46+/-4 and 53+/-4 mm Hg; P=0.30) in SPH and PPH patients. However, PPH-PASMCs had a higher resting [Ca2+]cyt than cells from patients with SPH and nonpulmonary hypertension disease. Consistently, PPH-PASMCs had a more depolarized Em than SPH-PASMCs. Furthermore, KV currents were significantly diminished in PPH-PASMCs. Because of the dysfunctional KV channels, the response of [Ca2+]cyt to the KV channel blocker 4-aminopyridine was significantly attenuated in PPH-PASMCs, whereas the response to 60 mmol/L K+ was comparable to that in SPH-PASMCs.

CONCLUSIONS

These results indicate that KV channel function in PPH-PASMCs is inhibited compared with SPH-PASMCs. The resulting membrane depolarization and increase in [Ca2+]cyt lead to pulmonary vasoconstriction and PASMC proliferation. Our data suggest that defects in PASMC KV channels in PPH patients may be a unique mechanism involved in initiating and maintaining pulmonary vasoconstriction and appear to play a role in the pathogenesis of PPH.

Short-term outcome and predictors of adverse events following pulmonary thromboendarterectomy

Pulmonary complications including hypoxemia, right heart failure, and prolonged ventilation may follow pulmonary thromboendarterectomy (PTE) performed via cardiopulmonary bypass (CPB) with deep hypothermic circulatory arrest. Seventeen adult patients have undergone PTE at the University of Maryland Medical System during the preceding 3 years. From these patients, clinical and hemodynamic parameters were tabulated pre-CPB, post-CPB, at admission to the intensive care unit (ICU), and prior to discontinuation of invasive monitoring in the ICU. Data on anthropometric variables, survival, and times of extracorporeal circulation, mechanical ventilation, and hospital stay were also collected. The mean values for pulmonary arterial systolic and diastolic pressures and pulmonary vascular resistance (PVR) decreased significantly from pre-CPB values after PTE (all p < 0.05). Mild mixed acidosis present at ICU admission resolved prior to discharge (p = 0.002). The length of mechanical ventilation time was positively correlated with the absolute post-CPB PVR and negatively correlated with the relative change in central venous pressure (CVP) from pre-CPB to post-CPB values (r = 0.75, p = 0.037). Of the pre-CPB anthropometric variables, only body mass index was significantly higher in nonsurvivors (p = 0.037). Pulmonary artery pressures and vascular resistance fall significantly after PTE. A lower post-CPB PVR and a relatively decreased (i.e., from pre-CPB values) CVP predict reduced length of postoperative ventilation but not of the hospital stay. Mortality appears increased in patients with a large body habitus.

Primary pulmonary hypertension

Primary pulmonary hypertension (PPH) is a progressive disease characterised by raised pulmonary vascular resistance, which results in diminished right-heart function due to increased right ventricular afterload. PPH occurs most commonly in young and middle-aged women; mean survival from onset of symptoms is 2-3 years. The aetiology of PPH is unknown, although familial disease accounts for roughly 10% of cases, which suggests a genetic predisposition. Current theories on pathogenesis focus on abnormalities in interaction between endothelial and smooth-muscle cells. Endothelia-cell injury may result in an imbalance in endothelium-derived mediators, favouring vasoconstriction. Defects in ion-channel activity in smooth-muscle cells in the pulmonary artery may contribute to vasoconstriction and vascular proliferation. Diagnostic testing primarily excludes secondary causes. Catheterisation is necessary to assess haemodynamics and to evaluate vasoreactivity during acute drug challenge. Decrease in pulmonary vascular resistance in response to acute vasodilator challenge occurs in about 30% of patients, and predicts a good response to chronic therapy with oral calcium-channel blockers. For patients unresponsive during acute testing, continuous intravenous epoprostenol (prostacyclin, PGI2) improves haemodynamics and exercise tolerance, and prolongs survival in severe PPH (NYHA functional class III-IV). Thoracic transplantation is reserved for patients who fail medical therapy. We review the progress made in diagnosis and treatment of PPH over the past 20 years.

Alpha1L-adrenoceptors in canine pulmonary artery

The aim of this study was to characterize the alpha-adrenoceptors of the canine pulmonary artery. Arterial rings from lower lung lobes were suspended for isometric-tension recording in the presence of cocaine (5 x 10(-6) M), hydrocortisone (3 x 10(-5) M), propranolol (5 x 10(-6) M), and rauwolscine (10(-7) M) to inhibit neuronal uptake, extraneuronal uptake, and beta- and alpha2-adrenoceptors, respectively. Prazosin was more potent against contractions evoked by phenylephrine (pA2 of 9.7) compared with methoxamine (pA2 of 8.4). SZL49 (10(-8) and 3 x 10(-8) M), an irreversible alpha1-adrenergic antagonist, inhibited responses to phenylephrine but not methoxamine. With norepinephrine, low concentrations of prazosin (3 x 10(-10) M and 10(-9) M) caused inhibition of the concentration-response curve; a higher concentration (3 x 10(-9) M) failed to produced further inhibition, whereas increasing the concentration of the antagonist (to 10(-8) and 3 x 10(-8) M) caused further rightward shifts in the concentration-response curve. The Arunlakshana and Schild plot revealed two components corresponding to pA2 values of 9.8 and 8.4. After SZL49 (3 x 10(-8) M), the Arunlakshana and Schild plot for the interaction between norepinephrine and prazosin was linear and generated a pA2 of 8.3. Contractions evoked by phenylephrine were inhibited by the alpha1B/alpha1D-adrenoceptor antagonist, chloroethylclonidine (10(-5) M), or by the alpha1B-antagonist, risperidone (pA2 value of 8.5), but were relatively resistant to inhibition by the selective alpha1D-antagonist, BMY7378 (-log K(B) of 6.1). The results suggest that two alpha1-adrenoceptor subtypes mediate contraction of the canine pulmonary artery. One subtype has high affinity for prazosin (alpha1H, likely to be alpha1B), is activated by phenylephrine, and is inhibited by SZL49. The other subtype has lower affinity for prazosin (alpha1L), is stimulated by methoxamine, and is relatively resistant to SZL49. The physiologic agonist, norepinephrine, causes contraction by activating both subtypes.

The influence of continuous intravenous prostacyclin therapy for primary pulmonary hypertension on the timing and outcome of transplantation

BACKGROUND

Primary pulmonary hypertension (PPH) is a progressive disease with a median survival of less than 3 years from diagnosis. Medical management has typically consisted of anticoagulation and oral calcium channel blocking agents, whereas lung transplantation (LT) has been reserved for patients who are unresponsive to medical therapy. Continuous intravenous prostacyclin was introduced for patients who did not respond to calcium channel blockers and who would have required LT. We reviewed our experience with prostacyclin in LT candidates to study its effects on the timing and outcome of LT.

METHODS

We retrospectively reviewed the clinic and hospital records of patients with PPH who were both treated with prostacyclin and evaluated for LT. Additional information was obtained from the pulmonary vascular disease and lung transplantation databases.

RESULTS

A total of 42 patients were identified who received prostacyclin for the treatment of PPH and were evaluated for LT. Thirty-seven patients were accepted as LT candidates, 22 at The University of Maryland Medical Center (UMMC), 15 at other LT programs. Overall, 70% (27/37) of LT candidates were removed from the LT waiting list or had listing for LT deferred because of clinical improvement. In patients listed for LT before initiation of prostacyclin therapy, 55% (12/22) were removed from the active waiting list for 27.2+/-17 months (range 8 to 60), and 92% (11/12) remain on the inactive status. In patients who received prostacyclin before listing for LT, listing for LT was deferred in 94% (14/15) for 17.4+/-9 months (range 6 to 33 months) because of clinical stability or improvement. In all, 93% of patients (39/42) experienced an improvement in 1 or more New York Heart Association functional class. The hemodynamic profiles of the eight patients removed from the active waiting list at UMMC demonstrated increases of 55%+/-18% in cardiac output, and decreases of 14.3%+/-4.9% in mean pulmonary artery pressure and 36%+/-8.3% in total pulmonary resistance (p < 0.05). The 1-year survival rate for LT after prostacyclin therapy was 88% (7/8) at UMMC and 60% (3/5) at the other centers.

CONCLUSION

We conclude that prostacyclin therapy is an effective means of delaying, possibly indefinitely, the need for LT in patients with PPH and that excellent results can be obtained when LT is performed after prostacyclin therapy. Consideration should be given to initiating prostacyclin therapy in all patients whose conditions do not respond to conventional therapy before proceeding with transplantation.

Hypoxic pulmonary endothelial cells release a diffusible contractile factor distinct from endothelin

Hypoxia (0% O2) evokes a late-phase, endothelium-dependent contractile response in porcine isolated pulmonary arteries that may be caused by a cyclooxygenase-independent, endothelium-derived contractile factor. The aim of this study was to further analyze the mechanism underlying this hypoxic response. Proximal porcine pulmonary arterial rings were suspended for isometric tension recording in organ chambers. Hypoxia (0% O2) caused a late-phase, endothelium-dependent contractile response that was not inhibited by the endothelin (ET)A-receptor antagonist BQ-123 (10(-6) M), by the ETB-receptor antagonist BQ-788 (10(-7) M), or by their combination. In contrast, ET-1 caused a concentration-dependent contraction of arterial rings that was inhibited by BQ-123 (10(-6) M) and a relaxation that was abolished by BQ-788 (10(-7) M) or by endothelial cell removal. Therefore, the endothelium-dependent contraction to hypoxia is not mediated by ET. Hypoxia caused only relaxation in endothelium-denuded rings. However, when a pulmonary valve leaflet, a rich source of pulmonary endothelial cells, was placed into the lumen of endothelium-denuded rings, hypoxia caused a late-phase contractile response that was similar to that observed in arterial rings with native endothelium. This hypoxic contraction persisted in the presence of indomethacin (10(-5) M) and N-nitro-L-arginine methyl ester (3 x 10(-5) M) to block cyclooxygenase and nitric oxide synthase, respectively. These results suggest that hypoxic contraction of pulmonary arteries is mediated by a diffusible, contractile factor released from hypoxic endothelial cells. This contractile mediator is distinct from ET.

Medical and surgical treatment options for pulmonary hypertension

Significant advances in the treatment of pulmonary hypertension have been achieved in the past decade. Approximately one quarter of patients with primary pulmonary hypertension (PPH) can be effectively managed with chronic calcium channel blocker therapy; for the remainder, transplantation or continuous intravenous epoprostenol are complex but effective approaches. Epoprostenol therapy was initially envisioned as a bridge to transplantation, but recent experience has established this approach as an alternative to transplantation in some patients, with comparable survival rates. Not all patients derive benefit from epoprostenol, however, and adverse effects are common. Accordingly, patients who fall into New York Heart Association Functional Classes III and IV and who are refractory to oral vasodilator therapy should be evaluated both for the initiation of epoprostenol therapy and concurrent listing for transplantation. By delaying or avoiding transplantation through the use of epoprostenol, these patients may also benefit from ongoing research that targets novel therapeutic approaches and less cumbersome delivery mechanisms. Thus, epoprostenol may serve as a bridge to transplantation for some patients and to newer therapeutic options for others.

Heme oxygenase 2: endothelial and neuronal localization and role in endothelium-dependent relaxation

Heme oxygenase 2 (HO-2), which synthesizes carbon monoxide (CO), has been localized by immunohistochemistry to endothelial cells and adventitial nerves of blood vessels. HO-2 is also localized to neurons in autonomic ganglia, including the petrosal, superior cervical, and nodose ganglia, as well as ganglia in the myenteric plexus of the intestine. Enzyme studies demonstrated that tin protoporphyrin-9 is a selective inhibitor of HO with approximately 10-fold selectivity for HO over endothelial nitric oxide synthase (NOS) and soluble guanylyl cyclase. Inhibition of HO activity by tin protoporphyrin 9 reverses the component of endothelial-derived relaxation of porcine distal pulmonary arteries not reversed by an inhibitor of NOS. Thus, CO, like NO, may have endothelial-derived relaxing activity. The similarity of NOS and HO-2 localizations and functions in blood vessels and the autonomic nervous system implies complementary and possibly coordinated physiologic roles for these two mediators.