PubMed Health⌕ Search

Biomedical subjects

D N Cornfield

Publications and source records attributed to D N Cornfield.

At least 19 recordsLinked to original sources
PubMed1999

Inhaled nitric oxide in premature neonates with severe hypoxaemic respiratory failure: a randomised controlled trial.

BACKGROUND: Inhaled nitric oxide improves oxygenation and lessens the need for extracorporeal-membrane oxygenation in full-term neonates with hypoxaemic respiratory failure and persistent pulmonary hypertension, but potential adverse effects are intracranial haemorrhage and chronic lung disease. We investigated whether low-dose inhaled nitric oxide would improve survival in premature neonates with unresponsive severe hypoxaemic respiratory failure, and would not increase the frequency or severity of intracranial haemorrhage or chronic lung disease. METHODS: We did a double-blind, randomised controlled trial in 12 perinatal centres that provide tertiary care. 80 premature neonates (gestational age < or = 34 weeks) with severe hypoxaemic respiratory failure were randomly assigned inhaled nitric oxide (n=48) or no nitric oxide (n=32, controls). Our primary outcome was survival to discharge. Analysis was by intention to treat. We studied also the rate and severity of intracranial haemorrhage, pulmonary haemorrhage, duration of ventilation, and chronic lung disease at 36 weeks' postconceptional age. FINDINGS: The two groups did not differ for baseline characteristics or severity of disease. Inhaled nitric oxide improved oxygenation after 60 min (p=0.03). Survival at discharge was 52% in the inhaled-nitric-oxide group and 47% in controls (p=0.65). Causes of death were mainly related to extreme prematurity and were similar in the two groups. The two groups did not differ for adverse events or outcomes (intracranial haemorrhage grade 2-4, 28% inhaled nitric oxide and 33% control; pulmonary haemorrhage 13% and 9%; chronic lung disease 60% and 80%). INTERPRETATION: Low-dose inhaled nitric oxide improved oxygenation but did not improve survival in severely hypoxaemic premature neonates. Low-dose nitric oxide in the most critically ill premature neonates does not increase the risk of intracranial haemorrhage, and may decrease risk of chronic lung injury.

Administration, Inhalation↗
PubMed1999

Aerosol delivery of diethylenetriamine/nitric oxide, a nitric oxide adduct, causes selective pulmonary vasodilation in perinatal lambs.

Postnatal adaptation of the pulmonary circulation is mediated partly by endothelium-derived nitric oxide (NO). Recent studies have demonstrated that inhaled NO causes selective and sustained vasodilation in infants with persistent pulmonary hypertension of the newborn. Because the short half-life of NO limits its clinical application, we hypothesized that aerosol delivery of an NO-adduct, diethylenetriamine (DETANO), can cause sustained and selective pulmonary vasodilation. To test the acute effects of DETANO, we studied the pulmonary vascular response of late-gestation fetal lambs (n = 8; age = 138 days; term = 147) to aerosolized DETANO in the presence of an endothelium-derived NO inhibitor, nitro-L-arginine. To determine whether DETANO has a sustained effect, fetal lambs were ventilated with FiO2 0.10 before and 15 minutes after they were treated with aerosolized DETANO. Fetal lambs were acutely prepared. Nitro-L-arginine (1 mg/min x 30 minutes) was infused into the left pulmonary artery before ventilation with FiO2 1.00 for 30 minutes, followed by continued ventilation with FiO2 0.10 for 10 minutes. This represented the control period. Ventilation was continued with FiO2 1.00, and aerosolized DETANO was given in doses of 0.1, 0.4, and 1.0 mg. Fifteen minutes after the last dose of DETANO was administered, animals were ventilated with FiO2 0.10. In the control period, during ventilation with FiO2 0.10, left pulmonary artery flow was 122+/-33 mL/min and decreased to 104+/-22 mL/min. Aerosol delivery of DETANO increased left pulmonary artery flow to 176+/-26 mL/min (P<.05) and had no effect on aortic pressure or heart rate. After DETANO was administered, ventilation with FiO2 0.10 did not cause any change in left pulmonary artery flow. We conclude that DETANO can cause selective fetal pulmonary vasodilation. Aerosol delivery of DETANO may increase the clinical applications of NO.

Aerosols↗
PubMed1999

Multicenter randomized controlled trial of the effects of inhaled nitric oxide therapy on gas exchange in children with acute hypoxemic respiratory failure.

OBJECTIVES AND BACKGROUND: To determine whether inhaled nitric oxide (iNO) therapy can attenuate the progression of lung disease in acute hypoxemic respiratory failure, we performed a multicenter, randomized, masked, controlled study of the effects of prolonged iNO therapy on oxygenation. We hypothesized that iNO therapy would improve oxygenation in an acute manner, slow the rate of decline in gas exchange, and decrease the number of patients who meet pre-established oxygenation failure criteria. STUDY DESIGN: A total of 108 children (median age 2.5 years) with severe acute hypoxemic respiratory failure from 7 centers were enrolled. After consent was obtained, patients were randomized to treatment with iNO (10 ppm) or mechanical ventilation alone for at least 72 hours. Patients with an oxygenation index >/=40 for 3 hours or >/=25 for 6 hours were considered treatment failures and exited the study. RESULTS: Patient age, primary diagnosis, pediatric risk of mortality score, mode of ventilation, and median oxygenation index (35 +/- 22 vs 30 +/- 15; iNO vs control; mean +/- SEM) were not different between groups at study entry. Comparisons of oxygenation indexes during the first 12 hours demonstrated an acute improvement in oxygenation in the iNO group at 4 hours (-10.2 vs -2.7, mean values; P <.014) and at 12 hours (-9.2 vs -2.8; P <.007). At 12 hours 36% of the control group met failure criteria in contrast with 16% in the iNO group (P <.05). During prolonged therapy the failure rate was reduced in the iNO group in patients whose entry oxygenation index was >/=25 (P <.04) and in immunocompromised patients (P <.03). CONCLUSIONS: We conclude that iNO causes an acute improvement in oxygenation in children with severe AHRF. Two subgroups (immunocompromised and an entry oxygen index >/=25) appear to have a more sustained improvement in oxygenation, and we speculate that these subgroups may benefit from prolonged therapy.

Administration, Inhalation↗
PubMed1999

K+-channel blockade inhibits shear stress-induced pulmonary vasodilation in the ovine fetus.

To determine whether K+-channel activation mediates shear stress-induced pulmonary vasodilation in the fetus, we studied the hemodynamic effects of K+-channel blockers on basal pulmonary vascular resistance and on the pulmonary vascular response to partial compression of the ductus arteriosus (DA) in chronically prepared late-gestation fetal lambs (128-132 days gestation). Study drugs included tetraethylammonium (TEA; Ca2+-dependent K+-channel blocker), glibenclamide (Glib; ATP-dependent K+-channel blocker), charybdotoxin (CTX; preferential high-conductance Ca2+-dependent K+-channel blocker), apamin (Apa; low-conductance Ca2+-dependent K+-channel blocker), and 4-aminopyridine (4-AP; voltage-dependent K+-channel blocker). Catheters were inserted in the left pulmonary artery (LPA) for selective drug infusion and in the main pulmonary artery, aorta, and left atrium to measure pressure. An inflatable vascular occluder was placed around the DA. LPA flow was measured with an ultrasonic flow transducer. Animals were treated with saline, high- or low-dose TEA, Glib, Apa, CTX, CTX plus Apa, or 4-AP injected into the LPA. DA compression caused a time-related decrease in pulmonary vascular resistance in the control, Glib, Apa, CTX, CTX plus Apa, and low-dose TEA groups but not in the high-dose TEA and 4-AP groups. These data suggest that pharmacological blockade of Ca2+- and voltage-dependent K+-channel activity but not of low-conductance Ca2+- and ATP-dependent K+-channel activity attenuates shear stress-induced fetal pulmonary vasodilation.

4-Aminopyridine↗
PubMed1999

NO causes perinatal pulmonary vasodilation through K+-channel activation and intracellular Ca2+ release.

Evidence suggests that nitric oxide (NO) causes perinatal pulmonary vasodilation through K+-channel activation. We hypothesized that this effect worked through cGMP-dependent kinase-mediated activation of Ca2+-activated K+ channel that requires release of intracellular Ca2+ from a ryanodine-sensitive store. We studied the effects of 1) K+-channel blockade with tetraethylammonium, 4-aminopyridine, a voltage-dependent K+-channel blocker, or glibenclamide, an ATP-sensitive K+-channel blocker; 2) cyclic nucleotide-sensitive kinase blockade with either KT-5823, a guanylate-sensitive kinase blocker, or H-89, an adenylate-sensitive kinase blocker; and 3) blockade of intracellular Ca2+ release with ryanodine on NO-induced pulmonary vasodilation in acutely prepared late-gestation fetal lambs. N-nitro-L-arginine, a competitive inhibitor of endothelium-derived NO synthase, was infused into the left pulmonary artery, and tracheotomy was placed. The animals were ventilated with 100% oxygen for 20 min, followed by ventilation with 100% oxygen and inhaled NO at 20 parts/million (ppm) for 20 min. This represents the control period. In separate protocols, the animals received an intrapulmonary infusion of the different blockers and were ventilated as above. Tetraethylammonium (n = 6 animals) and KT-5823 (n = 4 animals) attenuated the response, whereas ryanodine (n = 5 animals) blocked NO-induced perinatal pulmonary vasodilation. 4-Aminopyridine (n = 5 animals), glibenclamide (n = 5 animals), and H-89 (n = 4 animals) did not affect NO-induced pulmonary vasodilation. We conclude that NO causes perinatal pulmonary vasodilation through cGMP-dependent kinase-mediated activation of Ca2+-activated K+ channels and release of Ca2+ from ryanodine-sensitive stores.

Animals↗
PubMed1999

Interactions of keratinocyte growth factor with a nitrating species after marrow transplantation in mice.

We reported that allogeneic T cells given to irradiated mice at the time of marrow transplantation stimulated tumor necrosis factor (TNF)-alpha, interferon (IFN)-gamma, and nitric oxide (. NO) production in the lung, and the addition of cyclophosphamide (known to stimulate superoxide production) favored the generation of a nitrating species. Although keratinocyte growth factor (KGF) prevents experimental lung injury by promoting epithelial repair, its effects on the production of inflammatory mediators has not been studied. KGF given before transplantation inhibited the T cell-induced increase in bronchoalveolar lavage fluid protein, TNF-alpha, IFN-gamma, and nitrite levels measured on day 7 after transplantation without modifying cellular infiltration or proinflammatory cytokines and inducible. NO synthase mRNA. KGF also suppressed. NO production by alveolar macrophages obtained from mice injected with T cells. In contrast, the same schedule of KGF failed to prevent permeability edema or suppress TNF-alpha, IFN-gamma, and. NO production in mice injected with both T cells and cyclophosphamide. Because only epithelial cells respond to KGF, these data are consistent with the production of an epithelial cell-derived mediator capable of downregulating macrophage function. However, the presence of a nitrating agent impairs KGF-derived responses.

Animals↗
PubMed1999

Randomized, controlled trial of low-dose inhaled nitric oxide in the treatment of term and near-term infants with respiratory failure and pulmonary hypertension.

UNLABELLED: Recent reports indicate that inhaled nitric oxide (iNO) causes selective pulmonary vasodilation, increases arterial oxygen tension, and may decrease the use of extracorporeal membrane oxygenation (ECMO) in infants with persistent pulmonary hypertension of the newborn (PPHN). Despite these reports, the optimal dose and timing of iNO administration in PPHN remains unclear. OBJECTIVES: To test the hypotheses that in PPHN 1) iNO at 2 parts per million (ppm) is effective at acutely increasing oxygenation as measured by oxygenation index (OI); 2) early use of 2 ppm of iNO is more effective than control (0 ppm) in preventing clinical deterioration and need for iNO at 20 ppm; and 3) for those infants who fail the initial treatment protocol (0 or 2 ppm) iNO at 20 ppm is effective at acutely decreasing OI. STUDY DESIGN: A randomized, controlled trial of iNO in 3 nurseries in a single metropolitan area. Thirty-eight children, average gestational age of 37.3 weeks and average age <1 day were enrolled. Thirty-five of 38 infants had echocardiographic evidence of pulmonary hypertension. On enrollment, median OI in the control group, iNO at 0 ppm, (n = 23) was 33.1, compared with 36.9 in the 2-ppm iNO group (n = 15). RESULTS: Initial treatment with iNO at 2 ppm for an average of 1 hour was not associated with a significant decrease in OI. Twenty of 23 (87%) control patients and 14 of 15 (92%) of the low-dose iNO group demonstrated clinical deterioration and were treated with iNO at 20 ppm. In the control group, treatment with iNO at 20 ppm decreased the median OI from 42.6 to 23.8, whereas in the 2-ppm iNO group with a change in iNO from 2 to 20 ppm, the median OI did not change (42.6 to 42.0). Five of 15 patients in the low-dose nitric oxide group required ECMO and 2 died, compared with 7 of 23 requiring ECMO and 5 deaths in the control group. CONCLUSION: In infants with PPHN, iNO 1): at 2 ppm does not acutely improve oxygenation or prevent clinical deterioration, but does attenuate the rate of clinical deterioration; and 2) at 20 ppm acutely improves oxygenation in infants initially treated with 0 ppm, but not in infants previously treated with iNO at 2 ppm. Initial treatment with a subtherapeutic dose of iNO may diminish the clinical response to 20 ppm of iNO and have adverse clinical sequelae.

Administration, Inhalation↗
PubMed1998

Effects of inhaled nitric oxide and oxygen in high-altitude pulmonary edema.

BACKGROUND: High-altitude pulmonary edema (HAPE) is characterized by pulmonary hypertension, increased pulmonary capillary permeability, and hypoxemia. Treatment is limited to descent to lower altitude and administration of oxygen. METHODS AND RESULTS: We studied the acute effects of inhaled nitric oxide (NO), 50% oxygen, and a mixture of NO plus 50% oxygen on hemodynamics and gas exchange in 14 patients with HAPE. Each gas mixture was given in random order for 30 minutes followed by 30 minutes washout with room air. All patients had severe HAPE as judged by Lake Louise score (6.4+/-0.7), PaO2 (35+/-3. 1 mm Hg), and alveolar to arterial oxygen tension difference (AaDO2) (26+/-3 mm Hg). NO had a selective effect on the pulmonary vasculature and did not alter systemic hemodynamics. Compared with room air, pulmonary vascular resistance fell 36% with NO (P<0.001), 23% with oxygen (P<0.001 versus air, P<0.05 versus NO alone), and 54% with NO plus 50% oxygen (P<0.001 versus air, P<0.005 versus oxygen and versus NO). NO alone improved PaO2 (+14%) and AaDO2 (-31%). Compared with 50% oxygen alone, NO plus 50% oxygen had a greater effect on AaDO2 (-18%) and PaO2 (+21%). CONCLUSIONS: Inhaled NO may have a therapeutic role in the management of HAPE. The combined use of inhaled NO and oxygen has additive effects on pulmonary hemodynamics and even greater effects on gas exchange. These findings indicate that oxygen and NO may act on separate but interactive mechanisms in the pulmonary vasculature.

Administration, Inhalation↗
PubMed1998

A maturational shift in pulmonary K+ channels, from Ca2+ sensitive to voltage dependent.

The mechanism responsible for the abrupt decrease in resistance of the pulmonary circulation at birth may include changes in the activity of O2-sensitive K+ channels. We characterized the electrophysiological properties of fetal and adult ovine pulmonary arterial (PA) smooth muscle cells (SMCs) using conventional and amphotericin B-perforated patch-clamp techniques. Whole cell K+ currents of fetal PASMCs in hypoxia were small and characteristic of spontaneously transient outward currents. The average resting membrane potential (RMP) was -36 +/- 3 mV and could be depolarized by charybdotoxin (100 nM) or tetraethylammonium chloride (5 mM; both blockers of Ca2+-dependent K+ channels) but not by 4-aminopyridine (4-AP; 1 mM; blocker of voltage-gated K+ channels) or glibenclamide (10 microM; blocker of ATP-dependent K+ channels). In hypoxia, chelation of intracellular Ca2+ by 5 mM 1, 2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid further reduced the amplitude of the whole cell K+ current and prevented spontaneously transient outward current activity. Under these conditions, the remaining current was partially inhibited by 1 mM 4-AP. K+ currents of fetal PASMCs maintained in normoxia were not significantly reduced by acute hypoxia. In normoxic adult PASMCs, whole cell K+ currents were large and RMP was -49 +/- 3 mV. These 4-AP-sensitive K+ currents were partially inhibited by exposure to acute hypoxia. We conclude that the K+ channel regulating RMP in the ovine pulmonary circulation changes after birth from a Ca2+-dependent K+ channel to a voltage-dependent K+ channel. The maturational-dependent differences in the mechanism of the response to acute hypoxia may be due to this difference in K+ channels.

Aging↗
PubMed1997

Diversity of response in vascular smooth muscle cells to changes in oxygen tension.

Hypoxia causes pulmonary vasoconstriction (HPV), but also dilation of systemic vessels and the ductus arteriosus. In the adult animal. HPV is initiated by inhibition of potassium current (IK) in the smooth muscle cells of small resistance arteries, which results in membrane depolarization and calcium entry through voltage-gated calcium channels. The oxygen-sensitive channels that initiate HPV are 4-aminopyridine (4-AP)-sensitive delayed rectifier channels (KDR), the most prominent of which has a conductance of 37 pS. In the fetus, hypoxia causes pulmonary vasoconstriction through inhibition of a calcium-sensitive potassium channel (KCa). In smooth muscle cells from the rabbit ductus arteriosus, which dilates in response to hypoxia, whole-cell potassium current is reversibly enhanced, rather than inhibited, by hypoxia. The principal oxygen-sensitive channel is inhibited by 4-AP and has a conductance of about 58 pS. There are morphological and electrophysiological differences between individual pulmonary artery smooth muscle cells, for example, in some cells IK is predominantly carried by KDR channels and in others by KCa channels. KDR cells are more common in the resistance pulmonary arteries and KCa in the conduit arteries. Responses of specific vessels (conduit, resistance; pulmonary, systemic, ductus) at different stages of development (fetal, neonatal and adult) to changes in oxygen tension may be determined by the distribution of a variety of ion channels in the smooth muscle cells.

Animals↗
PubMed1996

Oxygen causes fetal pulmonary vasodilation through activation of a calcium-dependent potassium channel.

At birth, pulmonary vasodilation occurs as air-breathing life begins. The mechanism of O2-induced pulmonary vasodilation is unknown. We proposed that O2 causes fetal pulmonary vasodilation through activation of a calcium-dependent potassium channel (KCa) via a cyclic nucleotide-dependent kinase. We tested this hypothesis in hemodynamic studies in acutely prepared fetal lambs and in patch-clamp studies on resistance fetal pulmonary artery smooth muscle cells. Fetal O2 tension (PaO2) was increased by ventilating the ewe with 100% O2, causing fetal total pulmonary resistance to decrease from 1.18 +/- 0.14 to 0.41 +/- 0.03 mmHg per ml per min. Tetraethylammonium and iberiotoxin, preferential KCa-channel inhibitors, attenuated O2-induced fetal pulmonary vasodilation, while glibenclamide, an ATP-sensitive K+-channel antagonist, had no effect. Treatment with either a guanylate cyclase antagonist (LY83583) or cyclic nucleotide-dependent kinase inhibitors (H-89 and KT 5823) significantly attenuated O2-induced fetal pulmonary vasodilation. Under hypoxic conditions (PaO2 = 25 mmHg), whole-cell K+-channel currents (Ik) were small and were inhibited by 1 mM tetraethylammonium or 100 nM charybdotoxin (CTX; a specific KCa-channel blocker). Normoxia (PaO2 = 120 mmHg) increased Ik by more than 300%, and this was reversed by 100 nM CTX. Nitric oxide also increased Ik. Resting membrane potential was -37.2 +/- 1.9 mV and cells depolarized on exposure to CTX, while hyperpolarizing in normoxia. We conclude that O2 causes fetal pulmonary vasodilation by stimulating a cyclic nucleotide-dependent kinase, resulting in KCa-channel activation, membrane hyperpolarization, and vasodilation.

Alkaloids↗
PubMed1996

Ventilation-induced pulmonary vasodilation at birth is modulated by potassium channel activity.

At birth, pulmonary blood flow rapidly increases 8- to 10-fold, and pulmonary arterial pressure falls by 50% within 24 h. The postnatal adaptation of the pulmonary circulation is mediated, in part, by endothelium-derived nitric oxide (EDNO). Recent studies suggest that EDNO may reduce vascular resistance, in part, by activating K+ channels. We hypothesized that K+ channels modulate the changes in pulmonary hemodynamics associated with birth. To test this hypothesis, we studied the effect of K+ channel inhibition on two separate, but interdependent stimuli: 1) mechanical ventilation with low inspired O2 concentrations (designed to maintain normal fetal blood gas tensions) and 2) mechanical ventilation with high inspired O2 concentrations. Tetraethyl-ammonium (TEA, 1 mg/min for 100 min; n = 5), a nonspecific K+ channel blocker, glibenclamide (Gli, 1 mg/min for 30 min; n = 6), an ATP-sensitive K+ channel blocker, or saline (n = 7) was infused into the left pulmonary artery (LPA) of acutely instrumented fetal lambs. The umbilical-placental circulation remained intact, and lambs were ventilated with 0.10 inspired O2 concentration (FIO2) for 60 min, followed by 1.0 FIO2 for 20 min. Neither TEA nor Gli had an effect on basal pulmonary tone. TEA attenuated the increase in LPA flow and decrease in pulmonary vascular resistance in response to mechanical ventilation with 0.10 and 1.0 FIO2; Gli had no effect. These results support the hypothesis that non-ATP-sensitive K+ channels modulate the transition from fetal to neonatal pulmonary circulation.

Adenosine Triphosphate↗
PubMed1995

Ca(2+)-inhibitable adenylyl cyclase modulates pulmonary artery endothelial cell cAMP content and barrier function.

Maintenance by the endothelium of a semi-permeable barrier is critically important in the exchange of oxygen and carbon dioxide in the lung. Intracellular free Ca2+ ([Ca2+]i) and cAMP are principal determinants of endothelial cell barrier function through their mutually opposing actions on endothelial retraction. However, details of the mechanisms of this antagonism are lacking. The recent discovery that certain adenylyl cyclases (EC 4.6.1.1) could be acutely inhibited by Ca2+ in the intracellular concentration range provided one possible mechanism whereby elevated [Ca2+]i could decrease cAMP content. This possibility was explored in pulmonary artery endothelial cells. The results indicate that a type VI Ca(2+)-inhibitable adenylyl cyclase exists in pulmonary artery endothelial cells and is modulated by physiological changes in [Ca2+]i. Furthermore, the results suggest the inverse relationship between [Ca2+]i and cAMP that is established by Ca(2+)-inhibitable adenylyl cyclase plays a critical role in modulating pulmonary artery endothelial cell permeability. These data provide evidence that susceptibility to inhibition of adenylyl cyclase by Ca2+ can be exploited in modulating a central physiological process.

Adenylyl Cyclases↗
PubMed1995

Hypoxia potentiates nitric oxide synthesis and transiently increases cytosolic calcium levels in pulmonary artery endothelial cells.

There is indirect, contradictory evidence both for increased and reduced synthesis of the endothelium-derived vasodilator, nitric oxide, in the pulmonary circulation during acute hypoxia. Therefore, we decided to directly measure the effect of acute hypoxia on nitric oxide production by cultured pulmonary endothelium. Because increases in the intracellular free calcium concentration are known to initiate nitric oxide synthesis, we also studied cytosolic calcium levels. We measured the accumulation of the stable nitric oxide metabolite, nitrite, in the fluid used to superfuse the cultured bovine pulmonary artery endothelial cells at an oxygen tension (PO2) of either 20.3 (normoxia) or 4.9 kPa (hypoxia) (152 or 37 mmHg). Intracellular calcium levels were measured with dual-excitation microfluorimetry after loading the cells with the fluorescent calcium indicator, fura 2. Basal NO synthesis, measured as nitrite accumulation over 10 min, was significantly higher under hypoxic than normoxic conditions (8.3 +/- 2.2 versus 4.6 +/- 0.8 nM). Hypoxia transiently increased cytosolic calcium concentration (from 113 +/- 10 to 231 +/- 45 nM). Ryanodine and thapsigargin (which deplete intracellular calcium stores), but not the removal of extracellular calcium, inhibited the hypoxic increase in cytosolic calcium, indicating that it resulted primarily from release of intracellular calcium. Bradykinin-elicited NO synthesis was potentiated by hypoxia. Bradykinin-induced increase in cytosolic calcium was not inhibited by hypoxia. We conclude that hypoxia acutely increases cytosolic calcium levels and basal and bradykinin-stimulated nitric oxide synthesis in pulmonary artery endothelium.

Animals↗
PubMed1994

Acute reductions in PO2 depolarize pulmonary artery endothelial cells and decrease [Ca2+]i.

Whereas pulmonary artery endothelial cells (PAECs) are sensitive to oxygen, neither the effect of an acute reduction in PO2 on PAEC membrane potential nor its effect on intracellular free Ca2+ ([Ca2+]i) is known. We hypothesized that in confluent primary cultures of PAECs, an acute decrease in PO2 would depolarize the cell membrane, inhibit Ca2+ influx, and reduce [Ca2+]i. To test this hypothesis, the membrane-sensitive fluorophore bis (1,3-dibutylbarbituric acid) trimethine oxonol (DiBAC4, 1 microM) and [Ca2+]i-sensitive probe fura 2 (3 microM) were used. A decrease in PO2 from 125 to 35 mmHg caused membrane depolarization and a 60 +/- 8% (data are means +/- SE) reduction in Ca2+ influx, estimated by manganese quenching of fura 2 fluorescence. While basal [Ca2+]i was 79 +/- 5 nM in normoxic cells, it decreased to 31 +/- 2 nM after 15 min of hypoxia. Decreasing the electrochemical gradient for Ca2+ entry with either low extracellular Ca2+, the K+ channel blockers tetraethylammonium or charybdotoxin, or blockade of Ca2+ entry with lanthanum decreased [Ca2+]i by 54-71% of that observed during an acute reduction in PO2. These results demonstrate that an acute reduction in PO2 1) depolarizes PAECs, 2) reduces Ca2+ influx, and 3) decreases [Ca2+]i, and that a similar reduction in [Ca2+]i was observed with interventions designed to reduce the electrochemical driving force for Ca2+ entry.

Animals↗
PubMed1994

Acute hypoxia causes membrane depolarization and calcium influx in fetal pulmonary artery smooth muscle cells.

Changes in oxygen tension in the perinatal period contribute to high pulmonary vascular tone in the fetus and the decline in resistance that occurs at birth. Distal pulmonary artery smooth muscle cells (PASMC) isolated from late-gestation ovine fetuses respond to acute hypoxia with an increase in cytosolic calcium concentration ([Ca2+]i) dependent on Ca2+ entry. The purpose of this study is to determine 1) whether acute hypoxia results in PASMC membrane depolarization, 2) whether Ca2+ entry was through voltage-operated calcium channels (VOCC), 3) the contribution of Ca(2+)-induced Ca2+ release (CICR) to the hypoxic response, and 4) whether a subset of K+ channels might serve as oxygen sensors in fetal PASMC. We used microfluorimetry on subconfluent monolayers of PASMC in primary culture loaded with either a membrane potential-sensitive dye, bis(1,3-dibutylbarbituric acid) trimethine oxonol (DiBAC4; DPASMC), to estimate membrane potential, or the Ca(2+)-sensitive fluorophore, fura 2, to measure [Ca2+]i. Hypoxia increased fluorescence from PASMC loaded with DiBAC4, consistent with membrane depolarization. Verapamil (an inhibitor of VOCC) attenuated, and BAY K 8644 (a VOCC facilitator) potentiated, the hypoxia-induced increase in [Ca2+]i, respectively. The hypoxic response was transient after treatment with ryanodine (10(-7) M), a blocker of calcium release from intracellular stores. Charybdotoxin (10(-7) M), an inhibitor of Ca(2+)-activated K+ channels, almost doubled [Ca2+]i, whereas glibenclamide (10(-5) M), an ATP-sensitive K(+)-channel antagonist, had no effect.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1993

Effects of oxygen and exogenous L-arginine on EDRF activity in fetal pulmonary circulation.

To determine whether L-arginine, the precursor of endothelium-derived relaxing factor (EDRF), increases vasodilator activity in the fetal pulmonary circulation, we studied its effects on basal pulmonary vascular tone and on pulmonary vasodilation stimulated by oxygen and acetylcholine (ACh) in chronically prepared late-gestation fetal lambs. L-Arginine infusion (30-300 mg over 10 min) into the left pulmonary artery (LPA) increased blood flow (18-57%) without changing pulmonary artery pressure. To determine whether O2-induced vasodilation involves EDRF and is augmented by L-arginine treatment, we infused L-arginine or NG-nitro-L-arginine (L-NNA), an inhibitor of EDRF synthesis, while increasing fetal PO2 6 Torr by delivering 100% O2 to the ewe for 120 min. In controls, LPA blood flow progressively increased from 106 +/- 13 ml/min (baseline) to 257 +/- 34 ml/min (peak) at 40 min of increased PO2 (P < 0.05, baseline vs. peak) but steadily returned toward baseline during the next hour. Treatment with L-NNA markedly attenuated O2-induced pulmonary vasodilation (P < 0.05 vs. control). L-Arginine infusion did not augment or sustain the O2-induced vasodilator response. We also examined whether L-arginine could sustain pulmonary vasodilation to ACh, another EDRF-dependent stimulus, and found that the EDRF substrate neither potentiated nor sustained the ACh response. We conclude that: in the fetal lung 1) exogenous L-arginine is a fetal pulmonary vasodilator, 2) increased PO2 augments EDRF activity in the fetal lung, and 3) supplemental L-arginine does not sustain either O2- or ACh-induced vasodilation.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗