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Biomedical subjects

R H Steinhorn

Publications and source records attributed to R H Steinhorn.

At least 19 recordsLinked to original sources
PubMed2001

Recombinant human superoxide dismutase enhances the effect of inhaled nitric oxide in persistent pulmonary hypertension.

We investigated the pulmonary vascular effects of superoxide dismutase (SOD) alone and in combination with inhaled nitric oxide (iNO) in newborn lambs with persistent pulmonary hypertension (PPHN) following prenatal ligation of the ductus arteriosus. In in vitro experiments, pretreatment with SOD significantly enhanced vascular relaxation in response to the NO donor S-nitrosyl-acetylpenicillamine (SNAP) in fifth-generation pulmonary arteries isolated from lambs with PPHN. In vivo treatment of fully instrumented newborn lambs with a single intratracheal dose of recombinant human CuZn SOD (rhSOD; 5 mg/kg) produced selective dilation of the pulmonary circulation. Further studies, of the combination of rhSOD and iNO, showed enhancement of the pulmonary vascular effects of iNO after brief periods of inhalation of 5 ppm and 80 ppm NO. We conclude that rhSOD reduces pulmonary vascular resistance and facilitates the action of iNO in a lamb model of PPHN. This suggests that rhSOD may prove to be an effective adjunctive treatment for newborns with PPHN.

Administration, Inhalation↗
PubMed2001

Pulmonary hypertension alters soluble guanylate cyclase activity and expression in pulmonary arteries isolated from fetal lambs.

The nitric oxide (NO)-guanosine 3',5'-cyclic monophosphate (cGMP) signaling pathway plays an important role in the pulmonary vascular transition at birth. We studied pulmonary arteries and veins isolated from normal late-gestation fetal lambs and from fetal lambs with persistent pulmonary hypertension (PPHN) following prenatal ligation of the ductus arteriosus. We additionally used double immunolabeling and immunoblot analysis to determine relative vascular contents of endothelial nitric oxide synthase (NOS-III) and soluble guanylate cyclase (sGC). Cyclic GMP content and sGC activity were significantly lower in arteries from hypertensive lambs than controls. A rank order for contents of both soluble guanylate cyclase and NOS-III was observed by both immunolabeling and immunoblotting: Control vein = Hypertensive vein > Control artery > Hypertensive artery. Our data demonstrate that the relative expression of sGC correlates well with the relative expression of NOS-III, and indicate the potential importance of soluble guanylate cyclase in the regulation of the perinatal pulmonary circulation. These data may help us understand vascular mechanisms producing PPHN, as well as patterns of response to exogenous NO.

Animals↗
PubMed2001

Altered endothelium-dependent relaxations in lambs with high pulmonary blood flow and pulmonary hypertension.

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

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed2001

C-type natriuretic peptide system in fetal ovine pulmonary vasculature.

C-type natriuretic peptide (CNP) is a recently described endothelium-derived relaxing factor. CNP relaxes vascular smooth muscle and inhibits smooth muscle proliferation by binding to natriuretic peptide receptor (NPR) type B (NPR-B) and producing cGMP. Lung parenchyma and fifth-generation pulmonary arteries (PA) and veins (PV) were isolated from late-gestation fetal lambs. All three types of NPR mRNA were detected in PA and PV by RT-PCR. CNP and NPR-B immunostaining was positive in pulmonary vascular endothelium and medial smooth muscle. CNP concentration-response curves of PA and PV were compared with those of atrial natriuretic peptide (ANP) by use of standard tissue bath techniques. CNP relaxed PV significantly better than PA. ANP relaxed PA and PV equally, but ANP relaxed PA significantly better than CNP. Pretreating PA and PV with natriuretic peptide receptor blocker (HS-142-1) or cGMP-dependent protein kinase inhibitor Rp-beta-phenyl-1- N2-etheno-8-bromoguanosine 3',5'-cyclic monophosphorothionate significantly inhibited the CNP relaxation response, indicating that the response was mediated through the NPR-cGMP pathway. We conclude that CNP is important in mediating pulmonary venous tone in the fetus.

Animals↗
PubMed2001

sGC and PDE5 are elevated in lambs with increased pulmonary blood flow and pulmonary hypertension.

Utilizing aortopulmonary vascular graft placement, we established a lamb model of pulmonary hypertension that mimics congenital heart disease with increased pulmonary blood flow. We previously demonstrated that endothelial nitric oxide synthase (eNOS) is increased in lambs at age 4 wk. However, these lambs display a selective impairment of endothelium-dependent pulmonary vasodilation that is suggestive of a derangement downstream of NO release. Thus our objective was to characterize potential alterations in the expression and activity of soluble guanylate cyclase (sGC) and phosphodiesterase type 5 (PDE5) induced by increased pulmonary blood flow and pulmonary hypertension. Late-gestational fetal lambs (n = 10) underwent in utero placement of an aortopulmonary vascular graft (shunt). Western blotting analysis on lung tissue from 4-wk-old shunted lambs and age-matched controls showed that protein for both subunits of sGC was increased in shunted lamb lungs compared with age-matched controls. Similarly, cGMP levels were increased in shunted lamb lungs compared with age-matched controls. However, PDE5 expression and activity were also increased in shunted lambs. Thus although cGMP generation was increased, concomitant upregulation of PDE5 expression and activity may have (at least partially) limited and accounted for the impairment of endothelium-dependent pulmonary vasodilation in shunted lambs.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed2000

Heterogeneous distribution of type I nitric oxide synthase in pulmonary vasculature of ovine fetus.

The nitric oxide/guanosine 3',5'-cyclic monophosphate pathway plays an essential role in mediating pulmonary vasodilation at birth. Small resistance arteries in the fetal lung are vessels of major significance in the regulation of pulmonary vascular tone. The present study is to determine that type I nitric oxide synthase (NOS-I) is present in ovine fetal pulmonary vasculature and that NOS-I is distributed heterogeneously in ovine fetal pulmonary circulation. We used reduced nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry and NOS-I immunohistochemistry to localize NOS-I in fetal sheep lungs and showed a colocalization for NADPH-d activity with NOS-I immunoreactivity. Strong NOS-I immunoreactivity was observed exclusively in the endothelium of the terminal bronchiole and respiratory bronchiole-associated arteries. As a comparison, adult sheep lung did not show positive immunoreactivity in the pulmonary endothelium. NOS-I was absent in the umbilical or systemic arteries from the ovine fetus, whereas abundant NOS-III immunoreactivity was present in these arteries. We conclude that NOS-I is present uniquely in the ovine fetal pulmonary circulation as opposed to the adult pulmonary or the fetal systemic circulation. NOS-I is distributed heterogeneously in the ovine pulmonary vasculature. We speculate that NOS-I plays an active role in the regulation of perinatal pulmonary circulation.

Amino Acid Sequence↗
PubMed2000

Successful lysis of an obstructive aortic and renal artery thrombus in a neonate on extracorporeal membrane oxygenation.

We describe a neonate on venoarterial extracorporeal membrane oxygenation (ECMO) with acute renal failure associated with extensive aortic and bilateral renal artery thrombosis. Concurrent anticoagulation and continuous systemic thrombolytic therapy with tissue plasminogen activator (t-PA) resulted in complete thrombolysis as evaluated by Doppler flow. The relative risk and benefits of thrombolytic therapy in heparinized patients undergoing ECMO needs to be further studied.

Aortic Diseases↗
PubMed2000

Site-specific effect of guanosine 3',5'-cyclic monophosphate phosphodiesterase inhibition in isolated lamb lungs.

OBJECTIVE: To determine the effect of combining inhaled nitric oxide (NO) with an inhibitor of guanosine 3',5'-cyclic monophosphate-specific phosphodiesterase on total and segmental lung resistances. STUDY DESIGN: A controlled laboratory study in isolated blood-perfused lungs prepared from lambs. SETTING: Animal research facility affiliated with a university teaching hospital. SUBJECTS: Five newborn lambs at <48 hrs of life. INTERVENTIONS: Isolated blood-perfused lungs were prepared and treated with indomethacin (40 microg/mL) to inhibit prostaglandin synthesis. After a baseline period of normoxia (28% oxygen), pulmonary hypertension was induced with the thromboxane mimetic U46619 (0.1-0.4 microg/kg/min). During pulmonary hypertension, lungs were studied with inhaled NO only, with infusion of zaprinast only (0.25 mg/kg bolus and 0.05 mg/kg/min infusion), and with a combination of the two. For each study condition, the total pressure decrease across the lung was measured, and the inflow-outflow occlusion technique was used to partition the total pressure gradient measured at constant flow (100 mL/kg/min) into gradients across relatively noncompliant large arteries and veins and more compliant small arteries and veins. MEASUREMENTS AND MAIN RESULTS: U46619 infusion produced significant pulmonary vasoconstriction. The combination of inhaled NO and zaprinast decreased the total pressure decrease across the lung significantly more than NO alone. This effect was primarily attributable to a significantly greater decrease in gradient across the small artery segment after inhaled NO and zaprinast compared with NO alone. CONCLUSIONS: Guanosine 3',5'-cyclic monophosphate phosphodiesterase inhibition with zaprinast enhances the effect of inhaled NO, particularly in conditions in which small arteries represent the site of resistance. Phosphodiesterase inhibition may be a promising adjunct to inhaled NO for the treatment of persistent pulmonary hypertension.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1999

Alveolar capillary dysplasia: diagnostic potential for cardiac catheterization.

OBJECTIVE: Alveolar capillary dysplasia is a rare cause of persistent pulmonary hypertension of the newborn. Infants with this condition die despite maximal medical intervention including inhaled nitric oxide therapy and extracorporeal membrane oxygenation. To date, diagnosis of this lethal condition was made by open lung biopsy or during postmortem examination. We examined the possibility that distinct cardiac catheterization findings could be used in the diagnosis of this lethal disorder. STUDY DESIGN: We present three infants with fatal persistent pulmonary hypertension of the newborn refractory to extracorporeal membrane oxygenation and inhaled nitric oxide therapy, two with postmortem autopsy confirmation of alveolar capillary dysplasia. Each infant underwent cardiac catheterization to complete the diagnostic evaluations. RESULTS: Significant right ventricular hypertension and normal pulmonary venous return were demonstrated, but a markedly diminished or absent capillary blush phase was noted in each infant. This finding is distinct from the normal capillary blush seen in infants with persistent pulmonary hypertension of the newborn of other etiologies. CONCLUSION: Cardiac catheterization may provide a useful alternative to tissue examination in the diagnosis of alveolar capillary dysplasia.

Angiography↗
PubMed1999

The pathophysiology of pulmonary hypertension in congenital heart disease.

Congenital heart disease with increased pulmonary blood flow commonly leads to the development of pulmonary hypertension and increased vascular reactivity. These serious sequelae are associated with the following two major categories of congenital heart defects: those resulting in increased pulmonary blood flow and increased pulmonary arterial pressure and those resulting in increased pulmonary venous pressure. Recent evidence that the pulmonary vascular endothelium is an important determinant of vascular tone has led to the hypothesis that endothelial injury, secondary to congenital heart disease with increased pulmonary blood flow, disrupts these regulatory mechanisms and thereby plays a role in the development of pulmonary hypertension and its associated increased vascular reactivity. In many animal models, endothelial dysfunction is a precursor for smooth muscle dysfunction, and there is an apparent progression from endothelial dysfunction to smooth muscle dysfunction as vascular changes progress. We established a chronic model of pulmonary hypertension with increased pulmonary blood flow in young lambs by placing a systemic-to-pulmonary shunt in utero. In this model, we found significant physiologic and molecular alternations of both the nitric oxide (NO) and endothelin signaling pathways, two important mechanisms by which the endothelium regulates pulmonary vascular tone. These alterations occur extremely early and precede severe anatomic changes. Early endothelial damage may contribute to the development of pulmonary hypertension and its associated enhanced pulmonary vascular reactivity.

Animals↗
PubMed1999

The cGMP-specific phosphodiesterase inhibitor E4021 dilates the pulmonary circulation.

We investigated the pulmonary vascular effects of E4021, a potent inhibitor of cGMP-specific phosphodiesterase, in control late-gestation fetal lambs, and in newborn lambs with persistent pulmonary hypertension (PPHN) after prenatal ligation of the ductus arteriosus. E4021 alone significantly relaxed fifth-generation pulmonary arteries isolated from control fetal lambs, an effect completely blocked after inhibition of nitric oxide synthase (NOS). In contrast, E4021 did not relax pulmonary arteries isolated from hypertensive lambs. Pretreatment with E4021 (10(-7) M) significantly enhanced relaxations to the NO donor S-nitrosyl-acetyl-penicilamine (SNAP) in arteries from both control and hypertensive lambs. In control, fully instrumented fetal lambs, infusions of E4021 (31 microgram/min) selectively dilated the pulmonary circulation, an effect again blocked after inhibition of NO synthase. Further studies were performed in newborn lambs with PPHN to study the vascular effects of E4021 alone, and in combination with inhaled NO. E4021 alone (1 to 100 microgram/kg/min) decreased pulmonary artery pressure (Ppa) in a dose-dependent fashion, and had minimal effect on systemic pressure. At the highest dose (100 microgram/kg/min), the dilation was selective for the pulmonary circulation. In subsequent protocols, E4021 (10 microgram/kg/min) significantly decreased Ppa and pulmonary vascular resistance (PVR), but these pulmonary vascular effects were not enhanced after NO inhalation at 0.5 or 5 ppm. We speculate that the lack of enhancement was due to the dramatic effects of E4021 alone. Potent, specific phosphodiesterase inhibitors such as E4021 may prove to be useful in the treatment of PPHN.

Analysis of Variance↗
PubMed1999

Pulmonary vascular biology during neonatal transition.

Although the normal pulmonary vascular transition at birth takes place quickly in the delivery room, it has its basis in the complex structural and biochemical development of the lung. It is not surprising that this process can be easily disrupted by factors such as prematurity, intrauterine hypoxia, and parenchymal lung disease. The stimuli that initiate and maintain the transition are only beginning to be understood. Understanding the normal structure and function of the neonatal lung provides the foundation that will enable clinicians to enhance resuscitation to accomplish a normal transition in the delivery room.

Embryonic and Fetal Development↗
PubMed1998

Heterogeneous distribution of soluble guanylate cyclase in the pulmonary vasculature of the fetal lamb.

BACKGROUND: Vascular segments in the fetal lung differ anatomically and functionally from one another. At birth, the nitric oxide (NO) pathway plays an integral role in reducing pulmonary vascular resistance through a marked vasodilation. However, the contributions of each vascular segment to this dilation are unclear. We sought to determine the distribution of soluble guanylate cyclase (sGC), the enzyme NO activates to induce vasodilation across the pulmonary vasculature. METHODS: Pulmonary airspaces were expanded with freezing compound and the pulmonary arterial tree was infused with barium sulfate gelatin. Soluble guanylate cyclase was localized by immunohistochemistry across the pulmonary vasculature of four near-term fetal lambs and its immunoreaction product was assessed by a semiquantitative method. The physiologic response of fourth- and fifth-generation arteries and veins isolated from age-matched lambs to NO was measured using standard tissue bath techniques. RESULTS: Clear differences in sGC immunostaining were present throughout the pulmonary vasculature: very weak to absent in large arteries accompanying bronchi, but intensely positive for veins. This pronounced staining for sGC in preacinar veins correlated with a 100-fold greater sensitivity to NO in veins compared to arteries of the same generation. The percentage of arteries staining positively approached 100% at the level of respiratory bronchioles and alveoli. CONCLUSIONS: These findings suggest that the increased response to NO in preacinar veins compared to that of arteries is in part due to increased sGC within venous vascular smooth muscle. Furthermore, intense staining within distal arteries implies a greater role for NO-mediated vasodilation within these segments.

Animals↗
PubMed1998

Contractile properties of intralobar pulmonary arteries and veins in the fetal lamb model of congenital diaphragmatic hernia.

BACKGROUND/PURPOSE: Pulmonary hypertension plays a significant role in the pathophysiology of congenital diaphragmatic hernia (CDH). Although there has been an intensive research effort directed at mediators that may cause pulmonary vasoconstriction, no single agent has been identified. The authors hypothesize that there may be an alteration in the cGMP-nitric oxide (NO) pathway of vasodilatation contributing to the pulmonary hypertension observed in CDH. The purpose of these studies is to begin to elucidate vasoactive properties of pulmonary vessels with particular attention to the cGMP-NO pathway of vasodilatation in fetal lambs with CDH. METHODS: Fourth-generation pulmonary arteries and pulmonary veins were dissected from both right and left lungs of eight, 139-day gestational fetuses with surgically created CDH. Vessels were studied with standard isolated tissue bath techniques. Experiments examined basal release of NO in endothelium-intact PVs and PAs of both right and left lungs by measuring the contractile force of vessels constricted with norepinephrine (NE) in the presence and absence of the nitric oxide synthase (NOS) inhibitor N(omega)-nitro-L-arginine (L-NA). Concentration-response curves to the vasodilating agents zaprinast and A23187 were also obtained in vessels contracted by NE. RESULTS: Left and right pulmonary artery responses to NE are enhanced over those of historic controls. Pretreatment of left pulmonary arteries with L-NA enhances the vasoconstrictor response to NE, whereas right PAs show no increased response. Relaxation responses to A23187 and zaprinast, in both left and right pulmonary arteries were not different from control lambs. Relaxation responses of both left and right pulmonary veins to A23187 and zaprinast are blunted compared with controls. This blunting is significantly more in left pulmonary veins than right. Further, right but not left pulmonary veins display enhanced vasoconstrictive response to NE after L-NA pretreatment. CONCLUSIONS: The NO-cGMP pathway of vasodilatation is abnormal in the near term, fetal lamb with CDH. These abnormalities were most apparent in pulmonary veins and may reflect abnormal NOS activity or content between left and right lungs of the fetal lamb with CDH. Pulmonary arteries from CDH lambs have basal and stimulated NO release equal to that of historic controls but appear to be hypersensitive to exogenous vasoconstrictors.

Animals↗
PubMed1998

Cervical ECMO cannula placement in infants and children: recommendations for assessment of adequate positioning and function.

BACKGROUND/PURPOSE: Cervical extracorporeal membrane oxygenation (ECMO) cannula position is often difficult to confirm by chest x-ray alone. Malposition requires a second surgery to rectify the problem. Reoperation places the patient at risk for infection, bleeding, or death. This study analyzes indications for cannula repositioning and suggests an alternative standard for intraoperative evaluation of catheter function as it relates to position. METHODS: The authors reviewed charts of 73 patients placed on arterio-venous ECMO through cervical vascular access. Reasons for repositioning of either cannula at the initial surgery or postoperatively were recorded. RESULTS: Of 73 patients, 18 (24.6%) required either arterial cannula or venous cannula repositioning. In 10 (55%) of these patients, cannula malposition was not detected by chest x-ray during the initial cannulation, and they therefore required a second cervical exploration for repositioning. CONCLUSIONS: Chest x-ray is not sensitive in demonstrating malpositioned cervical ECMO cannulae. Two-dimensional ECHO before wound closure, may be a superior, more cost effective means of assessing cannula placement and function than x-ray alone. Confirmation of cannula position and function, before wound closure, would reduce the risks involved with cervical reexploration.

Catheterization↗
PubMed1998

Increased endothelial NOS in lambs with increased pulmonary blood flow and pulmonary hypertension.

Altered pulmonary vascular reactivity is a source of morbidity and mortality for children with congenital heart defects and increased pulmonary blood flow. Nitric oxide (NO) is an important mediator of pulmonary vascular reactivity. The objective of this study was to characterize potential early alterations in expression, localization, and activity of endothelial NO synthase (eNOS) induced by increased pulmonary blood flow and pulmonary hypertension. Utilizing aortopulmonary vascular graft placement in the fetal lamb, we have established a unique animal model of pulmonary hypertension that mimics congenital heart disease with increased pulmonary blood flow. Ten fetal lambs underwent in utero placement of an aortopulmonary vascular graft (shunt). RNase protection assays and Western blotting were performed on lung tissue prepared from 4-wk-old shunt lambs and age-matched controls. eNOS mRNA (2.4:1, P < 0.05) and protein (2. 08:1, P < 0.05) were increased in lungs of shunt lambs. In situ hybridization and immunohistochemistry revealed that the increase was confined to the endothelium of pulmonary arteries. eNOS protein (1.55:1, P < 0.05) and tissue cGMP concentrations (2.1:1, P < 0.05) were also increased in isolated fifth-generation pulmonary arteries of shunt lambs. In addition, total lung eNOS activity was increased (2.9:1, P < 0.05). Thus we report a previously undescribed, early upregulation of eNOS gene expression and activity in lambs with increased pulmonary blood flow and pulmonary hypertension.

Animals↗
PubMed1998

Pulmonary and systemic effects of the phosphodiesterase inhibitor dipyridamole in newborn lambs with persistent pulmonary hypertension.

Nitric oxide (NO) relaxes vascular smooth muscle by increasing the intracellular concentration of cGMP. In the pulmonary circulation, cGMP is inactivated by specific phosphodiesterases (PDE5). Dipyridamole, a clinically approved drug, has inhibitory activity against PDE5 and has been reported to augment the response to inhaled NO in persistent pulmonary hypertension of the newborn (PPHN). We wished to determine whether dipyridamole alone, or in combination with NO, can be used to treat a newborn lamb model of PPHN. In newborn lambs with PPHN, dipyridamole infused at 0.02 mg/kg/min for 45 min alone, or in combination with 5 ppm of inhaled NO for the final 15 min, significantly decreased pulmonary and systemic blood pressure, decreased pulmonary vascular resistance, and increased pulmonary blood flow. There was no significant difference between the pulmonary vascular effects of 5 ppm NO alone compared with the effects of NO combined with dipyridamole. In control lambs, the 45-min infusion of dipyridamole did not change pulmonary pressure whereas systemic pressure decreased by 28 +/- 3%. These systemic effects in control lambs persisted 90 min after discontinuing the dipyridamole infusion. Systemic arteries isolated from both control and PPHN lambs were significantly more sensitive to dipyridamole than pulmonary arteries. We conclude that dipyridamole has significant hemodynamic effects in both the pulmonary and systemic circulations of newborn lambs with pulmonary hypertension as well as in the systemic circulation of newborn control lambs. The pronounced effects of dipyridamole on the systemic circulation limits its utility as an adjunct to inhaled NO in the treatment of PPHN.

Animals↗