Cyclin-stimulated binding of Cks proteins to cyclin-dependent kinases.

Although Cks proteins were the first identified binding partners of cyclin-dependent protein kinases (cdks), their cell cycle functions have remained unclear. To help elucidate the function of Cks proteins, we examined whether their binding to p34(cdc2) (the mitotic cdk) varies during the cell cycle in Xenopus egg extracts. We observed that binding of human CksHs2 to p34(cdc2) was stimulated by cyclin B. This stimulation was dependent on the activating phosphorylation of p34(cdc2) on Thr-161, which follows cyclin binding and is mediated by the cdk-activating kinase. Neither the inhibitory phosphorylations of p34(cdc2) nor the catalytic activity of p34(cdc2) was required for this stimulation. Stimulated binding of CksHs2 to another cdk, p33(cdk2), required both cyclin A and activating phosphorylation. Our findings support recent models that suggest that Cks proteins target active forms of p34(cdc2) to substrates.

Reduced incidence of hyaline membrane disease in extremely premature infants following delay of delivery in mother with preterm labor: use of ritodrine and betamethasone.

Data from two groups of infants (24 to 28 weeks' gestational age) excluded from a controlled trial of the use of calf lung surfactant extract for the prevention of hyaline membrane disease are reported. The two groups were excluded from the trial because the mothers had received betamethasone for greater than 24 hours prior to delivery or because, on admission to the hospital, labor was too far advanced for proper informed consent to enter the trial. Attempts were made to delay delivery of threatened premature labor by the use of ritodrine in all mothers without evidence of infection, heavy vaginal bleeding, or severe preeclampsia and to induce surfactant production by maternal injection of betamethasone. A prospective scoring system and respiratory support variables were used to compare the groups. Infants born to mothers who successfully completed this regimen had a 28% incidence of hyaline membrane disease v a 68% incidence in infants in whose mothers it was unsuccessful due to inability to stop advanced labor (P = .001). Inspired oxygen, mean airway pressure, and ventilator rate were lower and the ventilator efficiency index was higher in the treated group during the first 48 hours of life. An aggressive approach to postpone premature delivery and to induce surfactant production by using tocolysis and a regimen of glucocorticoids reduces the incidence of hyaline membrane disease in very premature infants, 24 to 28 weeks' gestation.

Double-blind clinical trial of calf lung surfactant extract for the prevention of hyaline membrane disease in extremely premature infants.

A prospective, double-blind, controlled trial was conducted to determine whether instillation of an exogenous surfactant into the lungs before the first breath could prevent hyaline membrane disease. The surfactant is calf lung lipid extracted from saline lung lavage. Entry was limited to infants who were 24 to 28 weeks' gestation, who were born at Children's Hospital of Buffalo, and whose mothers had not received betamethasone for more than 24 hours before birth. Treated infants received 3 mL (90 mg) of calf lung surfactant extract instilled into their trachea before the first breath; control infants received 3 mL of normal saline. A prospective scoring system and respiratory support variables were used to compare the groups. At 48 hours of age, only two of 14 calf lung surfactant extract-treated infants (14%) had hyaline membrane disease compared with seven of 13 control infants (54%) (P = .033). Inspired oxygen, mean airway pressure, ventilator rate and ventilator efficiency index were also lower in the treated group during the first 48 hours of life (P less than .01 to P less than .001). Calf lung surfactant extract instillation at birth appears to be an effective material and method of preventing hyaline membrane disease in extremely premature infants.

Persistence of fetal cardiopulmonary circulation: one manifestation of transient tachypnea of the newborn.

Five cyanotic newborn infants underwent cardiac catheterization between 8 and 36 hours of age with a tentative diagnosis of cyanotic congenital heart disease. All had normal cardiovascular anatomy. Cyanosis was the result of persistence of fetal cardiopulmonary circulation with right-to-left shunting across the ductus arteriosus. In all infants, cyanosis resolved spontaneously and the infants survived without sequelae. Admission chest roentgenograms of all infants showed marked hyperinflation of the lungs. Except for severe hypoxemia, the clinical presentation, chest films, and course of illness of these infants were consistent with transient tachypnea of the newborn. It is proposed that an increase in pulmonary vascular resistance, due to hyperinflation of the lungs, was the mechanism which reopened the fetal cardiopulmonary circulatory channels and produced hypoxemia, and that these infants suffered from a rare manifestation of a usually benign newborn respiratory condition. Further, given these pathophysiologic mechanisms, the use of continuous transpulmonary pressure gradients in the management of such infants would be contraindicated.

Transient tricuspid insufficiency of the newborn: a form of myocardial dysfunction in stressed newborns.

Fourteen term newborn infants have been recognized as having transient tricuspid insufficiency associated with significant perinatal stress. Five of these infants underwent cardiac catheterization for presumed congenital heart disease, but had only massive tricuspid valve insufficiency. The other nine infants were diagnosed on the basis of a murmur characteristic of tricuspid valve insufficiency and on other clinical grounds. All had a history of significant perinatal stress in the form of asphyxia with or without hypoglycemia. Frequently, congestive heart failure, persistent cyanosis, and ECG evidence of myocardial ischemia were present. Twelve of the 14 survived, and in each of them all cardiac signs and symptoms, including the murmur, spontaneously resolved. The two patients who died had histopathologic evidence of necrosis in the anterior papillary muscle of the tricuspid valve. The constant features of perinatal stress, ST-T wave abnormalities on the ECG, and spontaneous resolution of the transient tricuspid insufficiency strongly suggest that this syndrome is secondary to a reversible form of myocardial dysfunction, perhaps by affecting papillary muscle specifically. We believe that hypoxia with or without hypoglycemia precipitates the events leading to this clinical syndrome which is distinguishable from other cardiac abnormalities in the newborn by the history, distinctive murmur, and the ECG abnormalities.

High-versus low-threshold surfactant retreatment for neonatal respiratory distress syndrome.

UNLABELLED: Surfactant therapy has become an effective standard therapy for infants with respiratory distress syndrome (RDS). The first dose may be given either as prophylaxis immediately after delivery, or as rescue after an infant has developed RDS. Second and subsequent doses are currently recommended by the manufacturers to be administered at minimal levels of respiratory support. PURPOSE: This study compared the relative efficacy of administering second and subsequent doses of Infasurf surfactant at a low threshold (FIO(2) >30%, still requiring endotracheal intubation) versus a high threshold (FIO(2) >40%, mean airway pressure >7 cm H(2)O) of respiratory support. METHODS: A total of 2484 neonates received a first dose of surfactant; 1267 reached conventional retreatment criteria and were randomized to be retreated according to low- or high-threshold criteria. They were then retreated at a minimum of 6-hour intervals each time they reached their assigned threshold until receiving a maximum of 4 total doses. Subjects were stratified by whether they received their first dose by prophylaxis or rescue and by whether their lung disease was considered complicated (evidence of perinatal compromise or sepsis) or uncomplicated. RESULTS: Among the patients randomized, 33% of prophylaxis and 23% of rescue subjects met criteria for the complicated stratum. Although infants allocated to the high-threshold strategy were receiving slightly more oxygen at 72 hours, there was no difference in the number receiving mechanical ventilation at 72 hours or in the secondary respiratory outcomes (requirement for supplemental oxygen or mechanical ventilation at 28 days, supplemental oxygen at 36 weeks' postconceptional age, inspired oxygen concentration >60% at any time). However, there was a significantly higher mortality for infants with complicated RDS who had received retreatment according to the high-threshold strategy. CONCLUSIONS: We conclude that equal efficacy can be realized by delaying surfactant retreatment of infants with uncomplicated RDS until they have reached a higher level of respiratory support than is the current standard. We speculate that this would result in a substantial cost-saving from less utilization of drug. Conversely, we believe that infants with complicated RDS should continue to be treated by the low-threshold retreatment strategy, which is currently recommended by the manufacturers of the commercially available surfactants.

Pulmonary hemodynamics in fetal lambs during development at normal and increased oxygen tension.

During the latter third of gestation, the number of resistance vessels in the lungs of the fetal sheep increases by 10-fold even after correction for lung growth. We measured pulmonary arterial pressure and blood flow directly and calculated total pulmonary resistance (pressure divided by flow) in intrauterine fetal lambs at 93-95 days and at 136 days of gestation (term is 145-148 days). In addition, we used a hyperbaric chamber to increase oxygen tension in the fetuses and measured the effect on the pulmonary circulation. When corrected for wet weight of the lungs, pulmonary blood flow did not change with advancing gestation (139 +/- 42 to 103 +/- 45 ml.100 g-1.min-1). Pulmonary arterial pressure increased (42 +/- 5 to 49 +/- 3 mmHg); thus total pulmonary resistance increased with advancing gestation from 0.32 +/- 0.12 to 0.55 +/- 0.21 mmHg.100 g.min.ml-1. If the blood flow is corrected for dry weight of the lungs, neither pulmonary blood flow nor total pulmonary resistance changed with advancing gestation. Increasing oxygen tension increased pulmonary blood flow 10-fold in the more mature fetuses but only 0.2-fold in the less mature fetuses. At the normal low oxygen tension of the fetus, pulmonary blood flow does not increase between these two points of gestation in the fetal lamb despite the increase in vessel density in the lungs. However, during elevated oxygen tension, pulmonary blood flow does increase in proportion to the increase in vessel density.

Aggressive obstetric management in late second-trimester deliveries.

A 3-year experience during which fetal welfare was a major factor in the management of patients delivering between 24 and 27 weeks' gestation is presented. Sixty-two cases of women for whom prenatal assigned gestational age was between 24 and 27 weeks and who had a live fetus on admission were reviewed. Using discharge from the hospital as definition for survival, 34 of the 62 infants (55%) survived. Survival rates ranged from 36% at 24 weeks' gestation to 76% at 27 weeks' gestation. Three of the 34 survivors had major continuing problems at discharge. Of the various strategies used to improve perinatal outcome, the antenatal administration of betamethasone was associated with a significant (P less than .03) improvement in infant survival. The authors are encouraged by these results, which indicate that aggressive antenatal and postnatal efforts for pregnancies with gestational ages between 24 and 27 weeks are cost-effective, productive, and worthwhile.

Prostacyclin does not change during an oxygen induced increase in pulmonary blood flow in the fetal lamb.

The role of prostacyclin in mediating the increase in pulmonary blood flow caused by an increase in oxygen tension in the fetal lamb was investigated. Plasma concentrations of 6-keto-PGF1 alpha, the hydrolysis product of prostacyclin, were measured during an increase in pulmonary blood flow caused by a rise in oxygen tension in eight intrauterine fetal lambs. Fetal oxygen tension was increased by placing the pregnant ewes in a hyperbaric chamber and having them breathe 100% oxygen at three atmospheres absolute pressure. This increased fetal PaO2 from 27 +/- 3 to 60 +/- 6 torr (mean +/- S.E., p less than or equal to 0.0001) and increased the proportion of right ventricular output distributed to the fetal lungs from 6 +/- 2 to 45 +/- 7% (mean +/- S.E., p less than or equal to 0.001). However, the fetal plasma concentration of 6-keto-PGF1 alpha did not change, 186 +/- 26 to 208 +/- 40 pg/ml (mean +/- S.E.). Indomethacin decreased plasma concentrations of 6-keto-PGF1 alpha in each of three fetuses but did not decrease the proportion of right ventricular output distributed to their lungs. The increase in pulmonary blood flow caused by an increase in oxygen tension in the fetal lamb is not associated with an increase in plasma concentrations of 6-keto-PGF1 alpha. Prostacyclin does not appear to be involved in the increase in pulmonary blood flow caused by the increase in oxygen tension at birth.

Component-specific surface and physiological activity in bovine-derived lung surfactants.

Composition, surface activity and effects on pressure-volume (P-V) mechanics are examined for lavaged calf lung surfactant (LS) and the clinical exogenous surfactants Infasurf and Survanta. Lavaged LS and Infasurf had closely-matching compositions of phospholipids and neutral lipids. Survanta had higher levels of free fatty acids and triglycerides consistent with its content of added synthetic palmitic acid and tripalmitin. Infasurf and Survanta both contained less total protein than LS because of extraction with hydrophobic solvents, but the total protein content relative to phospholipid in Survanta was about 45% lower than in Infasurf. This difference was primarily due to surfactant protein (SP)-B, which was present by ELISA at a mean weight percent relative to phospholipid of 1.04% in LS, 0.90% in Infasurf, and 0.044% in Survanta. Studies on component fractions separated by gel permeation chromatography showed that SP-B was a major contributor to the adsorption, dynamic surface activity, and P-V mechanical effects of Infasurf, which approached whole LS in magnitude. Survanta had lower adsorption, higher minimum surface tension, and a smaller effect on surfactant-deficient P-V mechanics consistent with minimal contributions from SP-B. Addition of 0.05% by weight of purified bovine SP-B to Survanta did not improve surface or physiological activity, but added 0.7% SP-B improved adsorption, dynamic surface tension lowering, and P-V activity to levels similar to Infasurf. The SP-B content of lung surfactants appears to be a crucial factor in their surface activity and efficacy in improving surfactant-deficient pulmonary P-V mechanics.

Pre- versus post-ventilatory surfactant treatment in surfactant-deficient preterm lambs.

Twenty lambs at 127 days' gestation (term is 145 days) were randomly assigned to receive Infasurf (Calf Lung Surfactant Extract, ONY Inc., Amherst, NY) as an intratracheal bolus (3 mliter kg-1) either into a fluid-filled lung before ventilation (n = 10), or after ventilation for 5 min (n = 10). All lambs were surfactant-deficient by analysis of lung liquid obtained before surfactant administration. Lambs were then mechanically ventilated for 4 h. Oxygenation for the lambs given surfactant before ventilation did not change during the experiment; a/A pO2 was 0.50 +/- 0.13 at 1 h and 0.52 +/- 0.17 at 4 h. For the lambs given surfactant after initial ventilation, oxygenation decreased over time; a/A pO2 decreased from 0.48 +/- 0.23 at 1 h to 0.37 +/- 0.22 at 4 h (P < 0.05). Compliance, as calculated from the Ventilator Efficiency Index (VEI), improved over time in both groups, but was always significantly higher for lambs given surfactant before ventilation (P = 0.03). Histologic examination of the lungs revealed no differences between the groups; no evidence of epithelial denudation or hyaline membrane formation was seen in either group. Thus, ventilation of surfactant-deficient newborn lambs for 5 min before surfactant administration results in significantly decreased lung function when compared with surfactant administration before ventilation. These differences in lung function are not dependent on a histopathologic injury to the lung. It is possible that unevenness of deposition of the surfactant in an air-filled lung, compared to more uniform deposition in a fluid-filled unventilated lung, produces these differences.

Increased survival in low birth weight neonates given prophylactic surfactant.

OBJECTIVE: To compare the effectiveness of a prophylactic surfactant treatment strategy (PRO) to the effectiveness of a rescue (RESC) surfactant treatment strategy in patients at high risk for developing hyaline membrane disease (HMD). STUDY DESIGN: We analyzed data from a retrospective cohort consisting of all patients admitted to the neonatal intensive care units at the centers participating in the recently completed Infasurf-Survanta Comparative Trial. To be in the cohort, a patient had to be admitted during the trial, be <48 hours of age on admission, have a gestational age of <30 weeks, have a birth weight of 501 to 1250 gm, and be free of congenital anomalies. Twelve centers participated in this study. They contributed 1097 patients of whom 381 were treated with a PRO strategy. RESULTS: Survival was significantly higher in the PRO-strategy patients (84% vs 72%, p < 0.05) as was survival without oxygen requirement at a postconceptional age of 36 weeks (60% vs 46%, p < 0.05). In addition, the patients with PRO had a lower prevalence of grade III and IV intraventricular hemorrhage (IVH, 9% vs 14%, p < 0.05). All analyses were controlled for birth weight and type of study center. CONCLUSION: These data support the conclusion that using a PRO treatment strategy results in improved survival in patients at risk for developing HMD. A PRO treatment strategy may also decrease the likelihood of developing a severe IVH.

Impact of lung surfactant therapy on chronic lung diseases in premature infants.

Bronchopulmonary dysplasia (BPD) and chronic lung disease remain common complications of prematurity. This article addresses the evolution of BPD since its description in 1967, and the impact of surfactant replacement therapy on the incidence and characteristics of BPD. It also addresses the emergence of a form of chronic lung disease now seen in surfactant-treated premature infants who had no acute lung disease.

Use of surfactant in the delivery room.

Surfactant supplementation in prevention and treatment of surfactant deficient hyaline membrane disease has been widely studied. This article focuses on the prevention of HMD by preventilatory, tracheal instillation of surfactant in the delivery room.

Surfactant decreases pulmonary vascular resistance and increases pulmonary blood flow in the fetal lamb model of congenital diaphragmatic hernia.

INTRODUCTION: Experiments using animal models of neonatal respiratory distress syndrome have shown a decrease in pulmonary vascular resistance (PVR) with surfactant replacement, whereas studies with the lamb model of congenital diaphragmatic hernia (CDH) have demonstrated improvement in oxygenation and lung mechanics with this therapy. The aim of the present study was to measure the effects of surfactant replacement therapy on the pulmonary hemodynamics of the lamb model of CDH. METHODS: Ten lambs with surgically created CDH and five control lambs were instrumented at term, with the placental circulation intact. Ultrasonic flow probes were positioned around the main pulmonary artery and the common origin of the left and right pulmonary arteries to record total lung and main pulmonary artery blood flow. Catheters were inserted to record systemic, pulmonary, and left atrial pressure. Five CDH animals received 50 mg/kg of surfactant by tracheal instillation just before delivery. All 15 animals were then ventilated for 4 hours. RESULTS: Correcting the surfactant deficiency in the CDH lamb resulted in a significant increase in pulmonary blood flow, a decrease in PVR, and a reduction in right-to-left shunting. These improvements in hemodynamics were associated with a significant improvement in gas exchange over 4 hours. CONCLUSION: The fetal lamb model of CDH has elevated PVR in comparison to controls. Prophylactic surfactant therapy reduces this resistance and dramatically increases pulmonary blood flow while reducing extrapulmonary shunt. A surfactant deficiency may be partially responsible for the persistent pulmonary hypertension in neonates with CDH.

Pathophysiology of congenital diaphragmatic hernia. III: Exogenous surfactant therapy for the high-risk neonate with CDH.

Exogenous surfactant therapy (EST) in surfactant-deficient premature infants has been shown to improve lung compliance, decrease morbidity, and improve survival. Reports have demonstrated that newborns with congenital diaphragmatic hernia (CDH) have lung compliance, pressure-volume curves, and hyaline membrane formation resembling those changes seen in surfactant deficient premature newborns. We hypothesize that EST may also benefit infants with CDH. All high risk cases of prenatally diagnosed CDH at Children's Hospital of Buffalo from November 1988 to February 1991 were prospectively evaluated for EST. In those families who chose to participate, the surfactant preparation, Infasurf (100 mg/kg), was instilled into the newborn's lungs prior to the first breath. The remainder of the perinatal, neonatal, and surgical care was performed in a routine manner. Three high-risk prenatally diagnosed newborns with left CDH were treated with EST. All showed signs of decreased pulmonary compliance, but could still be adequately oxygenated and ventilated. Surgical correction was performed after stabilization and all required patch closures. Two of the three infants suffered no life-threatening episodes of pulmonary hypertension and all survived. These infants had many known indicators for poor outcome in CDH with an expected survival of less than 20%. We believe that EST in these neonates with CDH contributed to their survival with minimum morbidity. These results suggest that surfactant replacement for the high-risk neonate with CDH warrants further consideration and a randomized clinical trial is being planned.