Identifying abnormalities in symbiotic development between Trifolium spp. and Rhizobium leguminosarum bv. trifolii leading to sub-optimal and ineffective nodule phenotypes.

BACKGROUND AND AIMS: Legumes overcome nitrogen limitations by entering into a mutualistic symbiosis with N(2)-fixing bacteria (rhizobia). Fully compatible associations (effective) between Trifolium spp. and Rhizobium leguminosarum bv. trifolii result from successful recognition of symbiotic partners in the rhizosphere, root hair infection and the formation of nodules where N(2)-fixing bacteroids reside. Poorly compatible associations can result in root nodule formation with minimal (sub-optimal) or no (ineffective) N(2)-fixation. Despite the abundance and persistence of strains in agricultural soils which are poorly compatible with the commercially grown clover species, little is known of how and why they fail symbiotically. The aims of this research were to determine the morphological aberrations occurring in sub-optimal and ineffective clover nodules and to determine whether reduced bacteroid numbers or reduced N(2)-fixing activity is the main cause for the Sub-optimal phenotype. METHODS: Symbiotic effectiveness of four Trifolium hosts with each of four R. leguminosarum bv. trifolii strains was assessed by analysis of plant yields and nitrogen content; nodule yields, abundance, morphology and internal structure; and bacteroid cytology, quantity and activity. KEY RESULTS: Effective nodules (Nodule Function 83-100 %) contained four developmental zones and N(2)-fixing bacteroids. In contrast, Sub-optimal nodules of the same age (Nodule Function 24-57 %) carried prematurely senescing bacteroids and a small bacteroid pool resulting in reduced shoot N. Ineffective-differentiated nodules carried bacteroids aborted at stage 2 or 3 in differentiation. In contrast, bacteroids were not observed in Ineffective-vegetative nodules despite the presence of bacteria within infection threads. CONCLUSIONS: Three major responses to N(2)-fixation incompatibility between Trifolium spp. and R. l. trifolii strains were found: failed bacterial endocytosis from infection threads into plant cortical cells, bacteroid differentiation aborted prematurely, and a reduced pool of functional bacteroids which underwent premature senescence. We discuss possible underlying genetic causes of these developmental abnormalities and consider impacts on N(2)-fixation of clovers.

Cytoplasmic receptor for glucocorticoids in lung of the human fetus and neonate.

In fetal animals, glucocorticoids accelerate development of the lung and cause precocious appearance of alveolar surfactant. To determine if the human lung also can respond to corticosteroids, we examined lungs of the human fetus and neonate for both cytoplasmic binding and nuclear uptake of glucocorticoids. In slices of fetal lung incubated with [3H]dexamethasone at 2 degrees C, specific macromolecular binding occurs primarily in the "cytoplasmic" fraction. After further incubation at 37 degrees C. nearly 75% of the radioactivity localizes in the "nuclear" fraction with a concentration of 0.3 pmol/mg DNA at apparent dexamethasone saturation (47 nM). The cytoplasmic receptor binds dexamethasone in vitro with high affinity (dissociation constant = 8.9 nM), and the affinity of various other steroids correlates with their glucocorticoid potency. Receptor was present in lungs of fetuses and neonates of gestational age 12-43 wk, with a mean concentration in hysterotomy specimens of 0.24 pmol sites/mg cytosol protein. Similar binding activity was present at lower concentration in fetal liver, gut, kidney, heart, muscle, and skin. Cytoplasmic receptor was not detected in lung and liver of premature infants with respiratory distress syndrome. This deficit appears to result from increased levels of endogenous steroids (mean cortisol 45.5 micrograms/100 ml cytosol) as well as inactivation of receptor secondary to the illness. Thus, the lung of the human fetus and neonate contains the receptor mechanism necessary for direct responsiveness to glucocorticoids. These findings support the potential usefulness of these hormones in prevention of respiratory distress syndrome in the premature infant.

Glucocorticoid levels in maternal and cord serum after prenatal betamethasone therapy to prevent respiratory distress syndrome.

Serum glucocorticoid levels were determined in 20 mothers and 43 premature infants who received prenatal betamethasone therapy for prevention of respiratory distress syndrome (RDS). Maternal betamethasone peaked at 75 microg cortisol equivalents per 100 ml 1 h after injection of 12 mg steroid and declined to half by 6 h. Betamethasone in cord blood was 14.3 microg cortisol equivalents per 100 ml at 1 h, decreased to a level of 4.7 at 20 h, and was not detected 2 days after a second dose at 24 h. After the second dose, the mean level of cortisol in cord blood was 5.9 microg per 100 ml compared with 13.05 microg per 100 ml (p less than 0.001) in untreated premature infants. The unbound glucocorticoid activity in treated infants delivered 1-10 h after the second dose (mean, 8.4 microg per 100 ml) is similar to the unbound cortisol level after birth in untreated premature infants who develop RDS. These findings indicate that (a) serum glucocorticoid levels in the physiologic stress range can induce lung maturation in the human and (b) antenatal treatment with this dose of betamethasone does not expose the human fetus to potentially harmful pharmacologic levels of steroid.

The effect of inhaled nitric oxide on pulmonary function in preterm infants.

OBJECTIVE: Bronchopulmonary dysplasia (BPD) in preterm infants is associated with impaired alveolar growth, inflammation and airway hyperreactivity. In animal models of BPD, inhaled nitric oxide (NO) improves alveolar growth and inhibits airway smooth muscle proliferation. This study was designed to assess the effect of inhaled NO on resistance and compliance in ventilated preterm infants with evolving BPD. STUDY DESIGN: Expiratory resistance and compliance of the respiratory system were measured in 71 ventilated preterm infants, < or = 32 weeks gestation, randomized to NO (n=34) versus placebo (n=37) for > or = 24 days at 7 to 21 days of life. RESULT: At baseline expiratory resistance (231+/-71 versus 215+/-76 cm H(2)O l(-1) s(-1)) and compliance (0.49+/-0.14 versus 0.53+/-0.13 ml cm H(2)O(-1) kg(-1)) were comparable between placebo and NO groups, respectively. There was no effect of NO on expiratory resistance or compliance at 1 h, 1 week or 2 weeks of study gas administration. CONCLUSION: NO had no short- or medium-term effect on expiratory resistance or compliance in ventilated preterm infants.

Corticosteroid stimulation of phosphatidylcholine synthesis in cultured fetal rabbit lung: evidence for de novo protein synthesis mediated by glucocorticoid receptors.

To investigate further the mechanism whereby glucocorticoids accelerate the maturation of the pulmonary surfactant system, we studied both binding of glucocorticoids and their effect on phosphatidylcholine synthesis in organ cultures of fetal rabbit lung grown in serum-free medium. The greatest effect of dexamethasone (100 nM for 48 h) occurred at 24 days gestation when there was a 103% increase in the rate of choline incorporation into phosphatidylcholine and a 24% increase in the tissue content of disaturated phosphatidylcholine. Stimulation by corticosteroid was first observed after 12 h of exposure. Choline incorporation increased in a linear fashion for 36 h and then began to plateau; removal of the steroid after 24 h prevented any further increase in stimulation. The presence of other hormones in the culture medium was not a prerequisite for the corticosteroid action. Fetal sex had no influence on dexamethasone-induced phosphatidylcholine synthesis or on nuclear binding of dexamethasone. There was a striking similarity between the Kd values for specific nuclear binding of dexamethasone and cortisol (0.6 +/- 0.1 and 7.3 +/- 0.1 nM, respectively) and the concentrations for half-maximal stimulation of phosphatidylcholine synthesis (0.7 +/- 0.1 and 6.8 +/- 0.5 nM). The relative potencies of a number of steroids (100 nM) for both nuclear binding and stimulation of choline incorporation were the same: dexamethasone greater than cortisol greater than cortisone greater than corticosterone greater than dehydrocorticosterone, with no effect by progesterone, testosterone, or estradiol at this dose. Actinomycin D and cycloheximide blocked dexamethasone-induced phosphatidylcholine synthesis in a dose-dependent fashion. Actinomycin D had a marked effect if added at the initiation of hormone exposure, but little effect when added after 24 h, whereas cycloheximide was primarily effective between 24-48 h. These findings suggest that glucocorticoid stimulation of phosphatidylcholine synthesis in fetal lung is mediated by binding to specific receptors, with subsequent de novo synthesis of RNA and protein.

Theophylline treatment in the extubation of infants weighing less than 1,250 grams: a controlled trial.

The role of theophylline in weaning infants weighing less than 1,250 g at birth from mechanical ventilation was evaluated. Infants were randomized into control or theophylline treatment groups when they required minimal ventilatory support (peak inspiratory pressure 12 cm H2O, positive end-expiratory pressure 2 cm H2O, rate 12 breaths per minute, and FiO2 less than 0.3), and they were extubated 24 hours later. Infants required reintubation if they had (1) PaCO2 greater than 55 mm Hg and pH less than 7.20, (2) FiO2 greater than 0.5, or (3) apnea associated with a heart rate less than 100 beats per minute that required frequent stimulation (more than 20 episodes during a 16-hour period). Among 32 infants (birth weight less than 1,000 g) who reached minimal ventilatory support before seven days after delivery, 13 of 18 (72%) control infants required reintubation, whereas only four of 14 (28%) theophylline-treated infants required reintubation. On the other hand, among infants (birth weight less than 1,000 g) who reached minimal ventilatory support after seven days following delivery, only one of six (17%) of the control group required reintubation and no improvement could be seen with theophylline treatment. Similarly, among control infants (birth weight 1,001 to 1,250 g), only ten of 45 (23%) required reintubation after reaching low intermittent manditory ventilation settings. In summary, most infants recovering from respiratory distress syndrome who had birth weights (1) greater than 1,000 g or (2) less than 1,000 g and who were older than seven days could be successfully extubated from minimal ventilatory support without theophylline treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Outcome of very low birth weight infants: multiple gestation versus singletons.

OBJECTIVE: Multiple gestation infants are overrepresented in intensive care nurseries, and have been reported to have greater morbidity than singletons. A cohort of very low birth weight infants was examined to determine outcome of premature infants based on gestation type (multiple or single) and hypothesized that at this low birth weight, the outcome of the groups would be similar. METHOD: The sample was composed of all infants with birth weights < or = 1250 g born in a 10-year period (September 1977 through September 1987). Ninety-two percent (n = 364) of the infants discharged were seen at 1 year of age, and 73% (n = 249) were observed to school age. Morbidity was assessed by neurodevelopmental examinations and standard developmental tests. RESULTS: At 1 year of age and at school age, there were no differences in neurologic or neurosensory outcome between multiple gestation and single gestation infants. Logistic regression analyses were performed on the school age data, using cognitive outcome as the dependent variable and gestation type, birth weight, gestational age, intracranial hemorrhage, chronic lung disease, and a social risk factor as predictor variables. Gestation type was not associated with cognitive outcome at school age. Social risk factors and chronic lung disease showed an association with cognitive outcome at school age. CONCLUSIONS: Multiple gestation was not related to increased morbidity in this very low birth weight group. The developmental outcome of all infants with birth weights < or = 1250 g in this study was related to medical and social risk factors. These findings were consistent for a large group of infants over a 10-year period.

Nosocomial respiratory syncytial virus infections in an intensive care nursery: rapid diagnosis by direct immunofluorescence.

A nosocomial outbreak of respiratory syncytial virus infections involved 8 of 17 infants in an Intensive Care Nursery and one additional infant in the adjoining Newborn Nursery. Immunofluorescent staining of nasopharyngeal specimens was positive in six of seven virologically confirmed cases (86%). One additional case with negative viral cultures was also identified by this technique. Viral isolation in tissue cultures required an average of 4.9 days, whereas results of immunofluorescent studies were available in two to four hours. Rapid identification of infected infants by immunofluorescence permitted prompt institution of infection control measures.

Initial clinical trial of EXOSURF, a protein-free synthetic surfactant, for the prophylaxis and early treatment of hyaline membrane disease.

EXOSURF is a protein-free surfactant composed of 85% dipalmitoylphosphatidylcholine, 9% hexadecanol, and 6% tyloxapol by weight. A single dose of 5 mL of EXOSURF per kilogram body weight, which gave 67 mg of dipalmitoylphosphatidylcholine per kilogram body weight, or 5 mL/kg air was given intratracheally in each of two controlled trials: at birth to neonates 700 through 1350 g (the prophylactic trial, n = 74) or at 4 to 24 hours after birth to neonates greater than 650 g who had hyaline membrane disease severe enough to require mechanical ventilation (the rescue trial, n = 104). In both studies, time-averaged inspired oxygen concentrations and mean airway pressures during the 72 hours after entry decreased significantly (P less than .05) in the treated neonates when compared with control neonates. Thirty-six percent of the treated neonates in the rescue study had an incomplete response to treatment or relapsed within 24 hours, suggesting the need for retreatment in some neonates. In the rescue trial, risk-adjusted survival increased significantly in the treated group. There were no significant differences in intracranial hemorrhages, chronic lung disease, or symptomatic patent ductus arteriosus between control and treated infants in either trial.

Partial deficiency of surfactant protein B in an infant with chronic lung disease.

OBJECTIVE: To evaluate components of pulmonary surfactant and identify mutations in the surfactant protein B gene (SP-B) of a term infant with severe respiratory distress and chronic lung disease. PATIENT AND TESTING: Respiratory distress developed in an infant delivered at term, and he required extracorporeal bypass support for 2 weeks. Until his unexpected death at 9.5 months, he was ventilator and oxygen dependent and required continual dexamethasone therapy. Tracheobronchial lavage samples were analyzed for content of surfactant proteins (SPs), and DNA from blood samples were sequenced and analyzed by polymerase chain reaction restriction analysis for the presence of SP-B gene mutations. Surfactant lipid composition and function, the contents of SPs and their messenger RNAs (mRNAs), and the immunostaining pattern for SPs were determined in postmortem lung tissue. RESULTS: The lavage sample contained SP-A but not SP-B, and DNA restriction analysis indicated that the patient and his mother were heterozygous for the previously described 121ins2 mutation of SP-B. Postmortem lung tissue contained normal levels of SP-A and its mRNA, a low but detectable level of SP-B, and near normal content of SP-B mRNA. SP-C was abundant on staining, and some 6-kd precursor was present in tissue. A surfactant fraction was deficient in phosphatidylglycerol and was not surface active. On DNA sequencing, a point mutation was found in exon 7 of the patient's SP-B gene allele without the 121ins2 mutation, resulting in a cysteine for arginine substitution, and the father was a carrier for the same mutation. CONCLUSIONS: We describe a patient who is a compound heterozygote with a new mutation and only a partial deficiency of SP-B. Some forms of inherited SP-B deficiency may have low expression of immunoreactive and possibly functional SP-B with milder lung disease and longer survival. These infants may benefit from glucocorticoid therapy and may not develop antibodies to SP-B after either lung transplant or gene therapy.

Antenatal hormone therapy for improving the outcome of the preterm infant.

The value of antenatal therapy with glucocorticoids in improving the pulmonary outcome of preterm human infants was first demonstrated in 1972. Accelerated lung maturation occurs with physiologic stress levels of corticosteroid by receptor-mediated induction of specific developmentally regulated proteins. Since the first report by Liggins, multiple controlled trials have demonstrated a decreased number of cases of respiratory distress syndrome and mortality in treated infants. In addition, prenatal therapy leads to decreased intraventricular hemorrhage and hospital costs, and there is strong evidence for decreased incidence of both patent ductus arteriosus requiring therapy and necrotizing enterocolitis. The recommendations of the 1994 National Institutes of Health Consensus Conference include use of antenatal corticosteroids in virtually all women who are in labor when the fetus is between 24 to 34 weeks' gestation. The combination of antenatal corticosteroids with thyrotropin releasing hormone holds promise for further reducing the incidence and severity of respiratory distress syndrome and decreasing chronic lung disease in the preterm infant.

Antenatal hormone therapy for fetal lung maturation.

In summary, several agents have been studied, but only CS and thyroid hormones have been found to accelerate fetal lung maturation in animal studies. Thirty years of research has documented the beneficial effect of antenatal CS on fetal lung maturation, and antenatal steroid in combination with postnatal surfactant remains the mainstay of prevention and therapy for RDS in preterm infants. The efficacy and safety of postnatal steroids have yet to be demonstrated. Unfortunately, the addition of antenatal TRH to this regimen has not provided further benefit to the neonatal outcome of preterm infants as evidenced by the recently completed multicenter trials. In addition, the optimal number of courses of antenatal CS for lung maturation remains unclear.

Developmental follow-up of infants with persistent pulmonary hypertension of the newborn.

The authors review the relatively little follow-up of infants with PPHN, finding that a small number of studies found motor deficits and cognitive deficits in hyperventilated survivors, and that hearing loss has also been reported. Not enough data are available to separate the effects of various treatment modalities from the effect of the initial insult; however, no specific negative effects of hyperventilation have been found.

Pilot trial of late booster doses of surfactant for ventilated premature infants.

OBJECTIVE: Many premature infants at risk for bronchopulmonary dysplasia experience episodes of surfactant dysfunction with reduced surfactant protein B (SP-B). In this study, we investigated the safety and responses to booster doses of surfactant. STUDY DESIGN: A total of 87 infants, 500 to 1250 g birth weight, who were ventilated at 7 to 10 days received 2 or 3 doses of Infasurf (Calfactant, Forest Pharmaceuticals, St Louis, MO, USA) within a 1-week period. RESULT: For 184 doses, occurrence rates of transient bradycardia (13) and plugged endotracheal tube (5) were low, and no other adverse effects were noted. Treatment transiently improved the respiratory severity score (FiO(2) × mean airway pressure), SP-B content (+75%) and surface properties of isolated surfactant. Levels of eight proinflammatory cytokines in tracheal aspirate were interrelated and unchanged from baseline after surfactant treatment. CONCLUSION: Booster doses of surfactant for premature infants with lung disease are safe and transiently improve respiratory status as well as composition and function of endogenous surfactant.

Inhaled nitric oxide in premature infants: effect on tracheal aspirate and plasma nitric oxide metabolites.

OBJECTIVE: Inhaled nitric oxide (iNO) is a potential new therapy for prevention of bronchopulmonary dysplasia and brain injury in premature infants. This study examined dose-related effects of iNO on NO metabolites as evidence of NO delivery. STUDY DESIGN: A subset of 102 premature infants in the NO CLD trial, receiving 24 days of iNO (20 p.p.m. decreasing to 2 p.p.m.) or placebo, were analyzed. Tracheal aspirate (TA) and plasma samples collected at enrollment and at intervals during study gas were analyzed for NO metabolites. RESULT: iNO treatment increased NO metabolites in TA at 20 and 10 p.p.m. (1.7- to 2.3-fold vs control) and in plasma at 20, 10, and 5 p.p.m. (1.6- to 2.3-fold). In post hoc analysis, treated infants with lower metabolite levels at entry had an improved clinical outcome. CONCLUSION: iNO causes dose-related increases in NO metabolites in the circulation as well as lung fluid, as evidenced by TA analysis, showing NO delivery to these compartments.