Echocardiographic Pulmonary Hypertension Predicts Post-transplantation Renal Allograft Failure.

BACKGROUND: Pulmonary hypertension in the setting of renal transplantation has been associated with early allograft dysfunction and increased mortality, but this relationship has not been extensively studied. METHODS: We performed a retrospective cohort study of adult patients who underwent their first renal transplantation in the years 2003-2009 and had pre-transplantation echocardiograms. Pulmonary hypertension was defined as right ventricular systolic pressure ≥40 mm Hg in the absence of left-sided valvular disease and/or left ventricular ejection fraction ≤50%. Eighty-two of 205 patients (40%) met the inclusion criteria. The relationship between pulmonary hypertension and death-censored allograft failure (hemodialysis dependence or retransplantation) and serum creatinine was assessed with the use of Cox hazard regression and generalized mixed models. RESULTS: The presence of pulmonary hypertension was associated with a 3-fold increase in the risk of death-censored allograft failure (95% confidence interval, 1.20-7.32; P = .02). Failure rates were 19% at 24 months and 51% at 96 months for those with pulmonary hypertension versus 7% at 24 months and 20% at 86 months for those without pulmonary hypertension (P = .01). Among those without graft failure, there was an increase in creatinine levels after transplantation (P = .01). Effect estimates were unchanged by adjustment for multiple covariates and when pulmonary hypertension was defined as right ventricular systolic pressure ≥36 mm Hg. CONCLUSIONS: Pulmonary hypertension before renal transplantation carries a 3-fold increased risk of death-censored allograft failure. The relationship between the pulmonary circulation and renal allograft failure warrants further study.

Treatment of submassive pulmonary embolism with tenecteplase or placebo: cardiopulmonary outcomes at 3 months: multicenter double-blind, placebo-controlled randomized trial.

BACKGROUND: Acute pulmonary embolism (PE) can worsen quality of life due to persistent dyspnea or exercise intolerance. OBJECTIVE: Test if tenecteplase increases the probability of a favorable composite patient-oriented outcome after submassive PE. METHODS: Normotensive patients with PE and right ventricular (RV) strain (by echocardiography or biomarkers) were enrolled from eight hospitals. All patients received low-molecular-weight heparin followed by random assignment to either a single weight-based bolus of tenecteplase or placebo, administered in a double-blinded fashion. The primary composite outcome included: (i) death, circulatory shock, intubation or major bleeding within 5 days or (ii) recurrent PE, poor functional capacity (RV dysfunction with either dyspnea at rest or exercise intolerance) or an SF36(®) Physical Component Summary (PCS) score < 30 at 90-day follow-up. RESULTS: Eighty-three patients were randomized; 40 to tenecteplase and 43 to placebo. The trial was terminated prematurely. Within 5 days, adverse outcomes occurred in three placebo-treated patients (death in one and intubation in two) and one tenecteplase-treated patient (fatal intracranial hemorrhage). At 90 days, adverse outcomes occurred in 13 unique placebo-treated patients and five unique tenecteplase-treated patients Thus, 16 (37%) placebo-treated and six (15%) tenecteplase-treated patients had at least one adverse outcome (exact two-sided P = 0.017). CONCLUSIONS: Treatment of patients with submassive pulmonary embolism with tenecteplase was associated with increased probability of a favorable composite outcome.

Evidence for the role of p38 MAP kinase in hypoxia-induced pulmonary vasoconstriction.

Mitogen-activated protein (MAP) kinases regulate smooth muscle cell contraction. Hypoxia contracts pulmonary arteries by mechanisms that are incompletely understood. We hypothesized that hypoxic contraction of pulmonary arteries involves activation of the MAP kinases. To test this hypothesis, we studied the effects of SB-202190, a p38 MAP kinase inhibitor, PD-98059 and UO-126, two structurally different MEKK inhibitors, and anisomycin, a stimulator of p38 MAP kinase on acute hypoxia-induced contraction in rat conduit pulmonary artery rings precontracted with phenylephrine or KCl. Hypoxia induced a transient contraction, followed by a relaxation, and then a slowly developing sustained contraction. Hypoxia also significantly increased phosphorylation of p38 MAP kinase. SB-202190 did not affect the transient phase but abrogated the sustained phase of hypoxic contraction, whereas anisomycin enhanced both phases of contraction. SB-202190 also attenuated and anisomycin enhanced the phenylephrine-induced contraction. In contrast, PD-98059 and UO-126 had minimal effects on either hypoxic or phenylephrine-induced contraction. None of the treatments modified KCl-induced contraction. We conclude that p38, but not the ERK1/ERK2 MAP kinase pathway, mediates the sustained phase of hypoxic contraction in isolated rat pulmonary arteries.

Reduced oxygen tension increases atrial natriuretic peptide release from atrial cardiocytes.

To test the hypothesis that reduced oxygen tension stimulates cardiac atrial natriuretic peptide (ANP) secretion, we measured ANP release and expression in neonatal rat atrial and ventricular cardiac myocytes exposed to 45 min and 3, 6, and 24 hr of 3% or 21% oxygen. In atrial cardiocytes, the percentage of increase in culture media ANP concentration from baseline was greater in cells exposed to 3% than in cells exposed to 21% oxygen after 3 hr (814% +/- 52% vs. 567% +/- 33%, P < 0.05) and 6 hr of exposure (1639% +/- 91% vs. 1155% +/- 73%, P < 0.05). No differences in the percentage of increase in culture media ANP concentration was seen at 45 min (284% +/- 27% vs. 201% +/- 16%, P = NS) or 24 hr (2499% +/- 250% vs. 2426% +/- 195%). There was a significant increase in cellular ANP content between 3 and 24 hr in atrial cardiocytes exposed to 21% oxygen (105% +/- 40% vs. 296% +/- 60%, P < 0.05), but not in atrial cardiocytes exposed to 3% oxygen (118% +/- 20% vs. 180% +/- 26%, P = NS). Steady-state ANP mRNA levels in atrial cardiocytes were not affected by oxygen tension. In ventricular cardiocytes, oxygen tension did not affect ANP secretion, cellular ANP content, or steady-state ANP mRNA levels. We conclude that reduced oxygen tension increases release of ANP from atrial, but not ventricular cardiocytes and that this mechanism may contribute to the elevation in plasma ANP seen during acute hypoxia.

Vasoresponsiveness of sarcoidosis-associated pulmonary hypertension.

OBJECTIVE: To assess short-term and long-term responses to treatment with pulmonary vasodilators in patients with sarcoidosis-related pulmonary hypertension. METHODS: A prospective, observational study was performed on eight patients with moderate-to-severe sarcoidosis-related pulmonary hypertension. Patients underwent a short-term vasodilator trial, using inhaled nitric oxide (iNO), IV epoprostenol, and/or oral calcium-channel blockers. A favorable short-term response was considered a > or = 20% decrease in pulmonary vascular resistance (PVR). Five patients received long-term treatment with iNO (with one patient receiving epoprostenol in addition) and underwent follow-up hemodynamic and/or 6-min walk testing. Two patients received long-term treatment with calcium-channel blockers. RESULTS: Baseline (+/- SE) mean pulmonary artery pressure (mPAP) was 55 +/- 4 mm Hg and PVR was 896 +/- 200 dyne.s.cm(-5). A favorable short-term response was seen in seven of eight patients receiving iNO, four of six patients receiving epoprostenol, and two of five patients receiving calcium-channel blockers. With iNO, PVR decreased 31 +/- 5% (p = 0.006) and mPAP decreased 18 +/- 4% (p = 0.003); with epoprostenol, PVR decreased 25 +/- 6% (p = 0.016) and mPAP decreased 6 +/- 2% (p = not significant). Decreased systemic vascular resistance was the only significant response to treatment with calcium-channel blockers. Follow-up 6-min walk test results improved in all five patients receiving long-term treatment with iNO. Follow-up hemodynamic responses in three patients showed preserved vasoresponsiveness. These three patients subsequently died, as did the two patients receiving calcium-channel blockers. The two remaining patients continue to receive iNO. CONCLUSION: In the short term, pulmonary hypertension in patients with sarcoidosis is responsive to treatment with pulmonary vasodilators; these patients may benefit from long-term iNO therapy.

Phytoestrogens restore nitric oxide-mediated relaxation in isolated pulmonary arteries from chronically hypoxic rats.

Phytoestrogens derived from soybeans reverse endothelial dysfunction in a number of animal models of systemic vascular disease. Based on these studies, we hypothesized that phytoestrogens would reverse chronic hypoxia-induced endothelial dysfunction in rat pulmonary arteries. To test this hypothesis we examined the effect of genistein, the major phytoestrogen found in soybeans, on carbachol-induced relaxation in phenylephrine-constricted pulmonary artery rings isolated from normoxic rats and rats exposed to 14 days of hypobaric hypoxia. Compared with that in normoxic rats, the response to carbachol was impaired in pulmonary arteries isolated from rats exposed to chronic hypoxia. In normoxic rat pulmonary arteries, genistein (30 microM) did not change the maximum relaxation to carbachol. In contrast, genistein significantly enhanced the relaxation response to carbachol in pulmonary arteries from hypoxic rats, restoring it to the levels seen in normoxic rats. 17beta-estradiol (10 microM) and daidzein (30 microM), a structural analog of genistein lacking inhibitory effects on tyrosine kinases, also restored the relaxation response to carbachol in hypoxic rat pulmonary arteries. The nitric-oxide synthase inhibitor N(omega)-nitro-L-arginine (100 microM) completely blocked the genistein, daidzein, and 17beta-estradiol-induced restoration of the relaxation response to carbachol, whereas the estrogen receptor antagonist ICI 182,780 (10 microM) had no effect on the relaxation responses. We conclude that the phytoestrogens genistein and daidzein act like estrogen in restoring nitric oxide-mediated relaxation in chronically hypoxic rat pulmonary arteries and that this effect does not appear to be mediated by inhibition of tyrosine kinases or by known estrogen receptors.

EDHF contributes to strain-related differences in pulmonary arterial relaxation in rats.

Pulmonary arteries from the Madison (M) strain relax more in response to acetylcholine (ACh) than those from the Hilltop (H) strain of Sprague-Dawley rats. We hypothesized that differences in endothelial nitric oxide (NO) synthase (eNOS) expression and function, metabolism of ACh by cholinesterases, release of prostacyclin, or endothelium-derived hyperpolarizing factor(s) (EDHF) from the endothelium would explain the differences in the relaxation response to ACh in isolated pulmonary arteries. eNOS mRNA and protein levels as well as the NO-dependent relaxation responses to thapsigargin in phenylephrine (10(-6) M)-precontracted pulmonary arteries from the M and H strains were identical. The greater relaxation response to ACh in M compared with H rats was also observed with carbachol, a cholinesterase-resistant analog of ACh, a response that was not modified by pretreatment with meclofenamate (10(-5) M). N(omega)-nitro-L-arginine (10(-4) M) completely abolished carbachol-induced relaxation in H rat pulmonary arteries but not in M rat pulmonary arteries. Precontraction with KCl (20 mM) blunted the relaxation response to carbachol in M rat pulmonary arteries and eliminated differences between the M and H rat pulmonary arteries. NO-independent relaxation present in the M rat pulmonary arteries was significantly reduced by 17-octadecynoic acid (2 microM) and was completely abolished by charybdotoxin plus apamin (100 nM each). These findings suggest that EDHF, but not NO, contributes to the strain-related differences in pulmonary artery reactivity. Also, EDHF may be a metabolite of cytochrome P-450 that activates Ca(2+)-dependent K(+) channels.

The role of endothelin-1 in strain-related susceptibility to develop hypoxic pulmonary hypertension in rats.

The Hilltop (H) strain compared to the Madison (M) strain of Sprague-Dawley rats develops severe pulmonary hypertension in response to chronic hypoxia. We tested the hypothesis that endothelin-1 (ET-1) contributes to these strain-related differences. Plasma ET-1 content was not modified by chronic hypoxia in either strain. The lung ET-1 peptide and preproET-1 mRNA content were significantly increased to the same magnitude in both strains at 2 and 3 weeks of hypoxia. The ET(A) receptor mRNA increased more at 3 weeks of hypoxia in the lungs of H rats than in M rats, but not at other time points. The ET(B) receptor mRNA was not modified by hypoxia in either strain. After 3 days of normoxic recovery following 2 weeks of hypoxia, ET-1 protein and mRNA levels decreased to baseline levels in both rat strains. We conclude that ET-1 does not contribute to the development of cardiopulmonary differences between the H and M strains in response to hypoxia.

Prediction of post-extubation work of breathing.

OBJECTIVE: To evaluate which mode of preextubation ventilatory support most closely approximates the work of breathing performed by spontaneously breathing patients after extubation. DESIGN: Prospective observational design. SETTING: Medical, surgical, and coronary intensive care units in a university hospital. PATIENTS: A total of 22 intubated subjects were recruited when weaned and ready for extubation. INTERVENTIONS: Subjects were ventilated with continuous positive airway pressure at 5 cm H2O, spontaneous ventilation through an endotracheal tube (T piece), and pressure support ventilation at 5 cm H2O in randomized order for 15 mins each. At the end of each interval, we measured pulmonary mechanics including work of breathing reported as work per liter of ventilation, respiratory rate, tidal volume, negative change in esophageal pressure, pressure time product, and the airway occlusion pressure 100 msec after the onset of inspiratory flow, by using a microprocessor-based monitor. Subsequently, subjects were extubated, and measurements of pulmonary mechanics were repeated 15 and 60 mins after extubation. MEASUREMENTS AND MAIN RESULTS: There were no statistical differences between work per liter of ventilation measured during continuous positive airway pressure, T piece, or pressure support ventilation (1.17+/-0.67 joule/L, 1.11+/-0.57 joule/L, and 0.97+/-0.57 joule/L, respectively). However, work per liter of ventilation during all three preextubation modes was significantly lower than work measured 15 and 60 mins after extubation (p < .05). Tidal volume during pressure support ventilation and continuous positive airway pressure (0.46+/-0.11 L and 0.44+/-0.11 L, respectively) were significantly greater than tidal volume during both T-piece breathing and spontaneous breathing 15 mins after extubation (p < .05). Negative change in esophageal pressure, the airway occlusion pressure 100 msec after the onset of inspiratory flow, and pressure time product were significantly higher after extubation than during any of the three preextubation modes (p < .05). CONCLUSIONS: Work per liter of ventilation, negative change in esophageal pressure, the airway occlusion pressure 100 msec after the onset of inspiratory flow, and pressure time product all significantly increase postextubation. Tidal volume during continuous positive airway pressure or pressure support ventilation overestimates postextubation tidal volume.

Differences in acute hypoxic pulmonary vasoresponsiveness between rat strains: role of endothelium.

Intact Madison (M) rats have greater pulmonary pressor responses to acute hypoxia than Hilltop (H) rats. We tested the hypothesis that the difference in pressor response is intrinsic to pulmonary arteries and that endothelium contributes to the difference. Pulmonary arteries precontracted with phenylephrine (10(-7) M) from M rats had greater constrictor responses [hypoxic pulmonary vasoconstriction (HPV)] to acute hypoxia (0% O(2)) than those from H rats: 473 +/- 30 vs. 394 +/- 29 mg (P < 0.05). Removal of the endothelium or inhibition of nitric oxide (NO) synthase by N(omega)-nitro-L-arginine (L-NA, 10(-3) M) significantly blunted HPV in both strains. Inhibition of cyclooxygenase by meclofenamate (10(-5) M) or blockade of endothelin type A and B receptors by BQ-610 (10(-5) M) + BQ-788 (10(-5) M), respectively, had no effect on HPV. Constrictor responses to phenylephrine, endothelin-1, and prostaglandin F(2alpha) were similar in pulmonary arteries from both strains. The relaxation response to ACh, an NO synthase stimulator, was significantly greater in M than in H rats (80 +/- 3 vs. 62 +/- 4%, P < 0.01), but there was no difference in response to sodium nitroprusside, an NO donor. L-NA potentiated phenylephrine-induced contraction to a greater extent in pulmonary arteries from M than from H rats. These findings indicate that at least part of the strain-related difference in acute HPV is attributable to differences in endothelial function, possibly related to differences in NO production.

Genetic disruption of atrial natriuretic peptide causes pulmonary hypertension in normoxic and hypoxic mice.

To determine whether atrial natriuretic peptide (ANP) plays a physiological role in modulating pulmonary hypertensive responses, we studied mice with gene-targeted disruption of the ANP gene under normoxic and chronically hypoxic conditions. Right ventricular peak pressure (RVPP), right ventricle weight- and left ventricle plus septum weight-to-body weight ratios [RV/BW and (LV+S)/BW, respectively], and muscularization of pulmonary vessels were measured in wild-type mice (+/+) and in mice heterozygous (+/-) and homozygous (-/-) for a disrupted proANP gene after 3 wk of normoxia or hypobaric hypoxia (0.5 atm). Under normoxic conditions, homozygous mutants had higher RVPP (22 +/- 2 vs. 15 +/- 1 mmHg; P < 0.05) than wild-type mice and greater RV/BW (1.22 +/- 0.08 vs. 0.94 +/- 0.07 and 0.76 +/- 0.04 mg/g; P < 0.05) and (LV+S)/BW (4.74 +/- 0. 42 vs. 3.53 +/- 0.14 and 3.18 +/- 0.18 mg/g; P < 0.05) than heterozygous or wild-type mice, respectively. Three weeks of hypoxia increased RVPP in heterozygous and wild-type mice and increased RV/BW and RV/(LV+S) in all genotypes compared with their normoxic control animals but had no effect on (LV+S)/BW. After 3 wk of hypoxia, homozygous mutants had higher RVPP (29 +/- 3 vs. 23 +/- 1 and 22 +/- 2 mmHg; P < 0.05), RV/BW (2.03 +/- 0.14 vs. 1.46 +/- 0.04 and 1.33 +/- 0.08 mg/g; P < 0.05), and (LV+S)/BW (4.76 +/- 0.23 vs. 3.82 +/- 0.09 and 3.44 +/- 0.14 mg/g; P < 0.05) than heterozygous or wild-type mice, respectively. The percent muscularization of peripheral pulmonary vessels was greater in homozygous mutants than that in heterozygous or wild-type mice under both normoxic and hypoxic conditions. We conclude that endogenous ANP plays a physiological role in modulating pulmonary arterial pressure, cardiac hypertrophy, and pulmonary vascular remodeling under normoxic and hypoxic conditions.

C-type natriuretic peptide expression and pulmonary vasodilation in hypoxia-adapted rats.

Atrial and brain natriuretic peptides (ANP and BNP, respectively) are potent pulmonary vasodilators that are upregulated in hypoxia-adapted rats and may protect against hypoxic pulmonary hypertension. To test the hypothesis that C-type natriuretic peptide (CNP) also modulates pulmonary vascular responses to hypoxia, we compared the vasodilator effect of CNP with that of ANP on pulmonary arterial rings, thoracic aortic rings, and isolated perfused lungs obtained from normoxic and hypoxia-adapted rats. We also measured CNP and ANP levels in heart, lung, brain, and plasma in normoxic and hypoxia-adapted rats. Steady-state CNP mRNA levels were quantified in the same organs by relative RT-PCR. CNP was a less potent vasodilator than ANP in preconstricted thoracic aortic and pulmonary arterial rings and in isolated lungs from normoxic and hypoxia-adapted rats. Chronic hypoxia increased plasma CNP (15 +/- 2 vs. 6 +/- 1 pg/ml; P < 0.05) and decreased CNP in the right atrium (35 +/- 14 vs. 65 +/- 17 pg/mg protein; P < 0.05) and in the lung (3 +/- 1 vs. 14 +/- 3 pg/mg protein; P < 0.05) but had no effect on CNP in brain or right ventricle. Chronic hypoxia increased ANP levels fivefold in the right ventricle (49 +/- 5 vs. 11 +/- 2 pg/mg protein; P < 0.05) but had no effect on ANP in lung or brain. There was a trend toward decreased ANP levels in the right atrium (2,009 +/- 323 vs. 2,934 +/- 397 pg/mg protein; P = not significant). No differences in CNP transcript levels were observed between the two groups of rats except that the right atrial CNP mRNA levels were lower in hypoxia-adapted rats. We conclude that CNP is a less potent pulmonary vasodilator than ANP in normoxic and hypoxia-adapted rats and that hypoxia raises circulating CNP levels without increasing cardiopulmonary CNP expression. These findings suggest that CNP may be less important than ANP or BNP in protecting against hypoxic pulmonary hypertension in rats.

The efficacy of inhaled nitric oxide in the treatment of acute respiratory distress syndrome. An evidence-based medicine approach.

Nitric oxide is an endothelial relaxing factor. When given as an inhalational agent in the acute respiratory distress syndrome (ARDS), it vasodilates well ventilated areas of lung and improves oxygenation. Nitric oxide is a highly reactive molecule with myriad biologic effects, both potentially beneficial and toxic; its use as an inhalational agent in ARDS is experimental. This article reviews the available studies of inhaled nitric oxide.

Brain natriuretic peptide inhibits hypoxic pulmonary hypertension in rats.

Brain natriuretic peptide (BNP) is a pulmonary vasodilator that is elevated in the right heart and plasma of hypoxia-adapted rats. To test the hypothesis that BNP protects against hypoxic pulmonary hypertension, we measured right ventricular systolic pressure (RVSP), right ventricle (RV) weight-to-body weight (BW) ratio (RV/BW), and percent muscularization of peripheral pulmonary vessels (%MPPV) in rats given an intravenous infusion of BNP, atrial natriuretic peptide (ANP), or saline alone after 2 wk of normoxia or hypobaric hypoxia (0.5 atm). Hypoxia-adapted rats had higher hematocrits, RVSP, RV/BW, and %MPPV than did normoxic controls. Under normoxic conditions, BNP infusion (0.2 and 1.4 micro g/h) increased plasma BNP but had no effect on RVSP, RV/BW, or %MPPV. Under hypoxic conditions, low-rate BNP infusion (0.2 micro g/h) had no effect on plasma BNP or on severity of pulmonary hypertension. However, high-rate BNP infusion (1.4 micro g/h) increased plasma BNP (69 +/- 8 vs. 35 +/- 4 pg/ml, P < 0.05), lowered RV/BW (0.87 +/- 0.05 vs. 1.02 +/- 0.04, P < 0.05), and decreased %MPPV (60 vs. 74%, P < 0.05). There was also a trend toward lower RVSP (55 +/- 3 vs. 64 +/- 2, P = not significant). Infusion of ANP at 1.4 micro g/h increased plasma ANP in hypoxic rats (759 +/- 153 vs. 393 +/- 54 pg/ml, P < 0.05) but had no effect on RVSP, RV/BW, or %MPPV. We conclude that BNP may regulate pulmonary vascular responses to hypoxia and, at the doses used in this study, is more effective than ANP at blunting pulmonary hypertension during the first 2 wk of hypoxia.

Multiple cases of life-threatening adenovirus pneumonia in a mental health care center.

Eighteen cases of pneumonia developed during an outbreak of adenovirus infection in a chronic psychiatric care facility. The six patients most severely affected were admitted to the intensive care unit (ICU) at our institution. Four of these patients developed septic shock. We report the presentation, disease progression, and response to treatment of these patients. Clinical features consisted of high fever, nonproductive cough, and dense lower lobe infiltrates. Laboratory abnormalities included transient fall in white blood cell and platelet counts, and elevations of transaminases, lactate dehydrogenase (LDH), and creatinine phosphokinase (CPK). Five patients were intubated for hypoxemia and four developed the acute respiratory distress syndrome (ARDS) and septic shock (mean cardiac output, 14.1 +/- 1.3 L/min; cardiac index, 6.4 +/- 0.4 L/min/min2; systemic vascular resistance, 326 +/- 107 dyne cm/s2). All patients recovered and were discharged back to the chronic care facility except for one patient with chronic renal failure who died 2 mo after admission. Adenovirus (serotype 35) was isolated from the respiratory secretions of five patients and antibody titers increased 6-fold in the other. These patients constitute the largest series of patients with ARDS and septic shock caused by adenovirus pneumonia and the first outbreak of multiple cases of adenovirus pneumonia in immunocompetent civilian adults occurring from a single source.

Nonspecific endothelin-receptor antagonist blunts monocrotaline-induced pulmonary hypertension in rats.

Endothelin-1 (ET-1), a potent vasoactive and mitogenic peptide, has been implicated in the pathogenesis of several forms of pulmonary hypertension. We hypothesized that nonspecific blockade of ET receptors would blunt the development of monocrotaline (MCT)-induced pulmonary hypertension in rats. A single dose of the nonspecific ET blocker bosentan (100 mg/kg) given to intact rats by gavage completely blocked the pulmonary vasoconstrictor actions of Big ET-1 and partially blunted hypoxic pulmonary vasoconstriction. After 3 wk, MCT-injected (105 mg/kg sc) rats gavaged once daily with bosentan (200 mg/kg) had lower right ventricular (RV) systolic pressure (RVSP), RV-to-body weight (RV/BW) and RV-to-left ventricular (LV) plus septal (S) weight [RV/(LV+S)] ratios and less percent medial thickness of small pulmonary arteries than control MCT-injected rats. Lower dose bosentan (100 mg/kg) had no effect on these parameters after MCT or saline injection. Bosentan raised plasma ET-1 levels but had no effect on lung ET-1 levels. Bosentan (200 mg/kg) also had no effect on wet-to-dry lung weight ratios 6 days after MCT injection. When given during the last 10 days, but not the first 11 days of a 3-wk period after MCT injection, bosentan reduced RV/(LV+S) compared with MCT-injected controls. We conclude that ET-1 contributes to the pathogenesis of MCT-induced pulmonary hypertension and acts mainly during the later inflammatory rather than the acute injury phase after injection.

Atrial natriuretic peptide expression in rats with different pulmonary hypertensive responses to hypoxia.

Mechanisms that regulate atrial natriuretic peptide (ANP) expression during hypoxia are not well defined. We hypothesized that plasma immunoreactive ANP (irANP) and right heart irANP and ANP mRNA levels would be greater in a strain of Sprague-Dawley rats that develops more severe hypoxic pulmonary hypertension (H rats) than another strain (M rats). After 3 wk of hypoxia (0.5 atm), right ventricular systolic pressure (RVSP) and the right ventricle (RV) weight-to-left ventricle plus septum (LV (+) S) weight ratio [RV/(LV+S)] were greater in H rats than in M rats (70 +/- 4 vs. 40 +/- 2 mmHg and 0.59 +/- 0.02 vs. 0.50 +/- 0.02, respectively; P < 0.05 for both), but plasma ANP increased twofold and RV irANP and ANP mRNA increased fivefold in both rat strains. After 3 days of normoxic recovery from chronic hypoxia, RVSP, RV/(LV+S), and RV irANP and ANP mRNA levels decreased in M rats but not in H rats. Plasma irANP decreased to baseline levels in both rat strains. We conclude that, in addition to changes in RV pressure and hypertrophy, hypoxia acts through other mechanisms to modulate RV ANP synthesis and circulating ANP levels in hypoxia-adapted rats.

Atrial natriuretic peptide accounts for increased cGMP in hypoxia-induced hypertensive rat lungs.

Perfusate levels of nitric oxide (NO)-containing compounds and guanosine 3',5'-cyclic monophosphate (cGMP) are increased in hypoxia-induced hypertensive rat lungs. To test if increased cGMP was due to NO stimulation of soluble guanylate cyclase (sGC), we examined effects of inhibition of NO synthase with N omega-nitro-L-arginine (L-NNA) on perfusate accumulation of cGMP in physiological salt solution (PSS)-perfused hypertensive lungs isolated from rats exposed for 3-4 wk to hypobaric hypoxia. Because 200 microM L-NNA did not reduce cGMP, we next examined inhibitors of other pathways of stimulation of either sGC or particulate GC (pGC). Neither 5 microM Zn-protophorphyrin, an inhibitor of CO production by heme oxygenase, nor 10 mM aminotriazole, an inhibitor of H2O2 metabolism by catalase, reduced perfusate cGMP. However, an antiserum to atrial natriuretic peptide (ANP; 100 microliters antiserum/30 ml PSS), to inhibit ANP activation of pGC, completely prevented accumulation of the nucleotide. ANP antiserum was also more effective than L-NNA in reducing lung tissue cGMP. In contrast, L-NNA but not ANP antiserum increased resting vascular tone. These results suggested that whereas ANP determined perfusate and tissue levels of cGMP, NO regulated vascular tone. To test if perfusate cGMP reflected ANP stimulation of pGC in endothelial rather than smooth muscle cells, we examined effects of 10 microM Zaprinast, an inhibitor of cGMP hydrolysis in smooth muscle but not endothelial cells, and found no increase of cGMP in hypertensive lungs. ANP levels were not elevated in hypertensive lungs, and it is unclear by what mechanism the ANP-stimulated activity of pGC is increased in hypertensive pulmonary vascular endothelial cells.