Abnormal prenatal lung development resulting from maternal zinc deficiency in rats

The effect of maternal zinc deficiency during gestation on fetal lung development was studied. Sprague-Dawley rats were fed from the day of mating (day zero) a zinc deficient diet (0.4 +/- 0.1 ppm zinc) ad libitum, or a zinc supplemented control diet (100 ppm zinc) either ad libitum or with restricted intake. Fetuses were removed by cesarean section on days 17 to 21 of gestation. Fetuses of zinc deficient dams had smaller lungs both in absolute weight and relative to body weight on all days than did either ad libitum-fed or restricted-intake controls. On days 20 and 21 of gestation, concentration of fetal lung lecithin and phosphatidylethanolamine was lower in zinc deficient fetuses than in control groups, indicating a reduced production of pulmonary surfactant. The lecithin to sphingomyelin ratio of amniotic fluid was lower in zinc deficient rats than in controls on days 19, 20, and 21 of gestation. On days 18 through 21 of gestation, fetal lung DNA concentration in zinc deficient fetuses was lower than in controls, but there were no differences in fetal lung zinc concentration. Histological examination of lungs from zinc deficient fetuses at term showed air spaces that were slightly collapsed with smaller lumina of the alveolar ducts than in controls.     

Temporal pattern of accelerated lung growth after tracheal occlusion in the fetal rabbit

Tracheal occlusion in utero is a potent stimulus of fetal lung growth. We describe the early growth mechanics of fetal lungs and type II pneumocytes after tracheal ligation (TL). Fetal rabbits underwent TL at 24 days gestational age (DGA; late pseudoglandular stage; term = 31 to 33 days) and were sacrificed at time intervals ranging from 1 to 5 days after TL. Lung growth was measured by stereological volumetry and bromodeoxyuridine (BrdU) pulse labeling. Pneumocyte II population kinetics were analyzed using a combination of anti-surfactant protein A and BrdU immunohistochemistry and computer-assisted morphometry. Nonoperated littermates served as controls. TL resulted in dramatically enhanced lung growth (lung weight/body weight was 5.00 +/- 0.81% in TL versus 2.52 +/- 0.13% in controls at 29 DGA; P < 0.001, unpaired Student's t-test). Post-TL lung growth was characterized by a 3-day lag-phase typified by relative stagnation of growth, followed by distension of airspaces, increased cell proliferation, and accelerated architectural and cellular maturation by postligation days 4 and 5. During the proliferation phase, the replicative activity of type II cells was markedly increased (type II cell BrdU labeling index was 10.0 +/- 4.1% in TL versus 1.1 +/- 0.3% for controls at 29 DGA; P < 0.02), but their numerical density decreased (3.0 +/- 0.5 x 10(-3)/microm2 in TL versus 4.5 +/- 0.3 x 10(-3)/microm2 in controls at 29 DGA; P < 0.02), suggesting accelerated terminal differentiation to type I cells. In conclusion, post-TL lung development is characterized by a well defined temporal pattern of lung growth and maturation. The rabbit model lends itself well to study the regulatory mechanisms underlying accelerated fetal lung growth after TL.     

Fetal pulmonary development: the role of respiratory movements

The lung develops before birth as a collapsible, liquid-filled, organ. Throughout the later stages of gestation the fetal lungs are maintained at a level of expansion that is considerably greater than the level achieved as a result of passive equilibration between lung recoil and the chest wall. Fetal breathing movements (FBM) are a feature of normal fetal life and, as such, are used clinically in the assessment of fetal wellbeing. By opposing lung recoil, FBM help to maintain the high level of lung expansion that is now known to be essential for normal growth and structural maturation of the fetal lungs. During 'apnoeic' periods between successive episodes of FBM, active laryngeal constriction has the effect of opposing lung recoil by resisting the escape of lung liquid via the trachea. The prolonged absence or impairment of FBM is likely to result in a reduced mean level of lung expansion which can lead to hypoplasia of the lungs. There is clinical evidence, disputed by some, that the absence of FBM exacerbates the effects of other factors that are associated with lung hypoplasia, such as premature rupture of fetal membranes and oligohydramnios. Even in the absence of such factors, prolonged or repeated reductions or abolition of FBM may contribute to impairments of fetal lung development; FBM can be inhibited by fetal hypoxaemia, hypoglycaemia, maternal alcohol consumption, maternal smoking, intra-amniotic infection and maternal consumption of sedatives or narcotic drugs. Abnormal growth of the fetal lungs has relevance for postnatal respiratory health as it is now recognised that there may be only a limited capacity after birth for the restoration of normal pulmonary architecture following impaired intra-uterine lung development.     

The effects of nephrectomy on the developing fetus

Bilateral renal pathologies such as renal agenesis and renal dysplasia and lower urinary tract obstruction have been reported to result in pulmonary hypoplasia. Although oligohydramnios and resultant thoracic compression was suggested to be the cause of pulmonary hypoplasia, the exact mechanism is still unknown. Additionally the effect of absence of renal tissue on the development of the fetus has not been previously studied in detail. Therefore an experimental study was planned to investigate the effects of fetal nephrectomy on development. The fetuses from 27 New Zealand white rabbits were studied on the 23rd day of gestation. Right ovarian-end fetuses underwent bilateral nephrectomy or sham operations. Rabbits underwent hysterectomy on gestational day 30, and live fetuses were studied. Fetal body, lung, heart and liver weights, and lung, heart and thorax volumes were determined, organ weight/body weight ratios were calculated. Additionally, lungs were evaluated by histological examination. Although fetal nephrectomy resulted in decreased body weight (BW), lung, heart, liver weights and heart weight/BW ratio (p < 0.05), lung weight/BW and liver weight/BW ratios did not differ. Additionally, heart and thorax volumes were significantly decreased in the nephrectomy group (p < 0.05). However lung volume and thorax volume/BW ratio did not differ between groups. The histological evaluation of lungs revealed exfoliated cells but normal lung development. Bilateral fetal nephrectomy results in small-for-gestational age (SGA) status during birth without affecting the development of organic systems. Since SGA status may be associated with decreased placentofetal blood flow, bilateral nephrectomy may act through decreasing placentofetal blood flow and/or through the lack of kidney-related growth factors.     

Correction of congenital diaphragmatic hernia in utero VIII: Response of the hypoplastic lung to tracheal occlusion

Most fetuses with congenital diaphragmatic hernia (CDH) diagnosed before 24 weeks' gestation die despite optimal postnatal care. In fetuses with liver herniation into the chest, prenatal repair has not been successful. In the course of exploring the pathophysiology of CDH and its repair in fetal lambs, the authors found that obstructing the normal egress of fetal lung fluid enlarges developing fetal lungs, reduces the herniated viscera, and accelerates lung growth, resulting in improved pulmonary function after birth. They developed and tested experimentally a variety of methods to temporarily occlude the fetal trachea, allow fetal lung growth, and reverse the obstruction at birth. The authors applied this strategy of temporary tracheal occlusion in eight human fetuses with CDH and liver herniation at 25 to 28 weeks' gestation. With ongoing experimental and clinical experience, the technique of tracheal occlusion evolved from an internal plug (two patients) to an external clip (six patients), and a technique was developed for unplugging the trachea at the time of birth (Ex Utero Intrapartum Tracheoplasty [EXIT]). Two fetuses had a foam plug placed inside the trachea. The first showed dramatic lung growth in utero and survived; the second (who had a smaller plug to avoid tracheomalacia) showed no demonstrable lung growth and died at birth. Two fetuses had external spring-loaded aneurysm clips placed on the trachea; one was aborted due to tocolytic failure, and the other showed no lung growth (presumed leak) and died 3 months after birth. Four fetuses had metal clips placed on the trachea. All showed dramatic lung growth in utero, with reversal of pulmonary hypoplasia documented after birth. However, all died of nonpulmonary causes. Temporary occlusion of the fetal trachea accelerates fetal lung growth and ameliorates the often fatal pulmonary hypoplasia associated with severe CDH. Although the strategy is physiologically sound and technically feasible, complications encountered during the evolution of these techniques have limited the survival rate. Further evolution of this technique is required before it can be recommended as therapy for fetal pulmonary hypoplasia.     

Immunoreactive thromboxane synthase is measurable in ovine fetal hypothalamus as early as 86 days' gestation

Thromboxane A2 (TxA2) augments hypothalamus-pituitary-adrenal axis activity in both fetal and adult animals. We have proposed that TxA2 acts as a neuromodulator within the brain to stimulate the release of corticotropin releasing hormone (CRH) or arginine vasopressin (AVP) into the hypophyseal-portal blood. We performed the present experiments to identify immunoreactive thromboxane synthase (TxS) within fetal brain regions and to quantify developmental changes in the TxS immunoreactivity measurable within those regions. We found that immunoreactive TxS was present in fetal hypothalamus, pituitary, brainstem, and lung. In fetal hypothalamus, we found immunoreactive TxS in three identifiable molecular weights, approximately 65, 42, and 35 kD. In fetal pituitary and lung, we found the 65 and 35 kD forms, and in the brainstem we found only the 35 kD form. In fetal pituitary, there was a clear ontogenetic change in TxS immunoreactivity. The 42 kD TxS immunoreactivity was not present in the youngest fetal sheep studied (86-90 days' gestation), but was expressed in the other age groups (125-128, 135-139, 141-term, and postnatal ages). The other molecular weight forms appeared to increase in the older fetuses, but the changes were not significant. In the hypothalamus, all three forms of TxS were measurable at all ages, and there was no significant change in relative abundance. We conclude that immunoreactive TxS is present in the fetal brain throughout the last half of fetal gestation, but that the significance of multiple molecular weight forms is not clear.     

bcl-2 protein downregulation is not required for differentiation of multidrug resistant HL60 leukemia cells

Maternal administration of thyrotropin-releasing hormone, alone or in combination with corticosteroid, accelerates functional, morphologic and biochemical fetal lung maturation. However, the dose-response relationship of maternal thyrotropin-releasing hormone treatment and acceleration of fetal lung ultrastructural maturation or disaturated phosphatidylcholine content has not been investigated. We administered (i.p.) saline or thyrotropin-releasing hormone (0.2, 0.4 or 0.6 mg/kg/dose) to the pregnant Balb/c mouse on days 16 and 17 (b.i.d.) and on day 18 of gestation (1 h prior to killing). Morphometric ultrastructural analysis and quantitation of disaturated phosphatidylcholine content was done on the 18-day gestation fetal lung. Maternal thyrotropin-releasing hormone treatment resulted in an increase in the number of lamellar bodies and depletion of glycogen in fetal lung type II cells, and an increase in the lung airspace to parenchymal ratio. In addition, a striking difference in the pattern of lung growth was noted in the thyrotropin-releasing-hormone-treated (0.4 and 0.6 mg/kg/dose) groups. These lungs had larger air spaces, thinner alveolar septae and more air-blood barriers. Maternal thyrotropin-releasing hormone treatment did not influence fetal lung disaturated phosphatidylcholine content. We conclude that in the mouse, maternal thyrotropin-releasing hormone treatment enhances fetal lung structural maturation and propose that thyrotropin-releasing hormone plays a role in mammalian fetal lung growth.     

Ontogeny of 11 beta-hydroxysteroid dehydrogenase in ovine fetal kidney and lung

Eleven-beta-hydroxysteroid dehydrogenase (11 beta-HSD) is an enzyme which degrades 11-hydroxycorticosteroids to biologically inactive 11-oxocorticosteroids (cortisone and 11-dehydrocorticosterone). In some tissues, the activity of this enzyme prevents binding of cortisol to mineralocorticoid receptors. The present experiments were designed to test the hypothesis that the fetal kidney contains 11 beta-HSD, that the activity of 11 beta-HSD in fetal kidney increases near term, and that the fetal lung does not contain significant 11 beta-HSD activity. In kidney and lung tissue from 23 fetal sheep ranging in age between 86 and 145 days' gestation, we measured 11 beta-HSD activity. We found significant activity in fetal kidney (14-85% conversion from cortisol to cortisone) but no measurable activity in fetal lung (0-9%). The activity of 11 beta-HSD was significantly related to fetal gestational age (r = 0.76, n = 14). We conclude that 11 beta-HSD activity in the fetal kidney develops as a function of fetal gestational age, and that activity cannot be demonstrated in fetal lung. We speculate 11 beta-HSD in the fetus might function to alter the sensitivity of target organs to glucocorticoids, as well as to mineralocorticoids, and that the absence of activity in the lung allows a high sensitivity of pulmonary tissue to cortisol at the end of gestation.     

Pulmonary stress injury within physiological ranges of airway and vascular pressures

PURPOSE: The aim of this study was to assess the respective role of a small elevation in pulmonary capillary pressure, airway pressure, or both on alveolar capillary barrier permeability in an isolated perfused rat lung model. MATERIALS AND METHODS: Four groups were studied with low or high airway pressure (LA: 10 mL/kg (tidal volume); HA: 20 mL/kg), low or high pulmonary artery pressure (LP: 9 mm Hg; HP: 12 mm Hg): LALP, HALP, LAHP, and HAHP. The lungs were ventilated and perfused ex vivo for 30 minutes. Quantification of fluorescein isothiocyanate-labeled (FITC) dextran in bronchoalveolar lavage (BAL) fluid and radiolabeled tracers assessed alveolar capillary barrier permeability. RESULTS: BALF FITC-dextran was similar in the three groups with either one or two low-pressure parameters (LALP, LAHP, HALP), but high amounts were found in the HAHP group (375.2 x 10(-6) mg/mL v, respectively, 21.4, 26.2, and 30 x 10(-6) mg/mL, P = .0001). These results were consistent with the albumin space and extravascular lung water: higher values only in the HAHP group statistically different from the other groups (P < .002). Interalveolar pore examined with scanning electron microscopy showed an increase in diameters between LALP and HAHP (P < .0001). CONCLUSIONS: We can conclude that elevation of either the pulmonary artery pressure from 8 to 11 mm Hg or the alveolar pressure from 10 to 15 mm Hg alone does not change the permeability of the alveolar capillary membrane; however, there is an additive effect of these pressures.     

Effects of LDL-apheresis on serum lipoprotein (a), C4b binding protein, protein C, protein S, and complement components

The leakage of proteins in the immature neonatal lung can reduce the effect of exogenous surfactant. The effect of ethamsylate, a more specific prostaglandin inhibitor than indomethacin and aspirin-like drugs, on alveolar albumin leak was studied in a group of 27 immature newborn rabbits (gestational age 27 days). A pilot study was carried out using 4 animals and low-dose ethamsylate (10 mg/kg). A second group of animals (n = 12) received at birth, by intravenous injection, ethamsylate (50 mg/kg) and 10% human albumin (7 ml/kg). Animals not receiving ethamsylate (n = 11) served as control group. After 30 min of artificial ventilation with standard tidal volume (10 ml/kg) the lungs were lavaged and the amount of human albumin in lung lavage fluid was determined by immunodiffusion. No statistically significant differences were found in lung-thorax compliance and vascular to alveolar albumin leak between ethamsylate-treated animals and controls (p > 0.5). However, there was a statistically significant negative correlation between protein leak and lung compliance (r = -0.41; p < 0.04). These results suggest no direct influence of early ethamsylate administration on neonatal lung permeability in the immature neonate confirming that lung permeability is inversely related to compliance.     

The effect of bilateral thoracoplasty on lung development in fetal sheep

The relationship of breathing movements to lung development in the ovine fetus was investigated by partially removing ribs on each side of the chest and closing the deficiencies with silicone membranes at 114 days of gestation; the increase in compliance of the chest wall that resulted caused blunting of the amplitude of phasic negative pressures recorded in the trachea to less than 10 torr. Compared to sham operated controls (n = 5), the lungs of the thoracoplasty group (n = 5) at term weighed significantly (P less than 0.05) less, both wet (1.5 +/- 0.2 v. 2.3 +/- 0.1% of body weight) and dry (0.14 +/- 0.01 v. 0.18 +/- 0.01% of body weight. In addition, DNA content of the thoracoplasty group was less than that of the control group (0.47 +/- 0.05 mg v. 0.72 +/- 0.20 mg). Distensibility of the left lung with air at 40 cmH20 was less than in the thoracoplasty group than in controls (10.0 +/- 2.0 v. 18.9 +/- 3.0 ml.kg-1 body weight) but no differences were found in the concentrations of saturated phosphatidylcholine in lung tissue and lavage fluid, in DNA concentrations or in the amount of lung water (as % of wet weight of lung). It is concluded that phasic negative pressures of normal intensity are necessary for normal development of the fetal lungs.     

Planned vaginal delivery versus elective caesarean section: a study of 705 singleton term breech presentations

To define the pathology of bronchopulmonary dysplasia (BPD) in surfactant-treated patients (S-BPD), we reviewed 22 BPD patients (14 S-BPD and eight non-surfactant-treated [NS-BPD]) and 15 age-matched controls, the lungs from which had been processed after formalin inflation. These were studied for surfactant therapy, postconceptional age, crown-rump length, weight at autopsy, radial alveolar count (RAC), mean linear intercept (MLI), RAC/MLI ratio, and amount and extent of fibrosis. On trichrome staining, there was no alveolar septal fibrosis in the control group, whereas there was mild to moderate alveolar septal fibrosis in 5 of 14 S-BPD patients, of which three had fibrosis in most or all of the acini. In contrast, seven of eight NS-BPD had moderate to severe alveolar septal fibrosis in scattered acini throughout the lung. The patients were divided into two groups, with the first group having a postconceptional age at the time of death of up to 40 weeks' gestation. In group 1, the RAC in S-BPD (nine patients) was significantly lower than that of the controls (seven patients); mean, 4.14 and 5.13, respectively (P = .016), whereas the RAC in the NS-BPD (four patients) and the MLI in both S-BPD and NS-BPD were not statistically significantly different. In group 2, those with adjusted age greater than term, the mean RAC, a measure of acinar complexity, was 3.89 in the S-BPD (five patients) and 3.90 in the NS-BPD (four patients), whereas in the control group (eight patients), it was 5.79 (P = .0007). The mean MLI, a measure of alveolar size, was 0.21 and 0.17 in the S-BPD and NS-BPD groups, respectively, each of which was significantly greater than the mean value of 0.12 in the control group (P = .0003). The comparison of RAC/MLI ratios showed similar statistically significant differences. Based on these results, we conclude that (1) the amount of alveolar septal fibrosis is substantially less and tends to be more diffuse in S-BPD than in NS-BPD; (2) during the period after birth, there is a partial to complete arrest in acinar development (alveolar saccular and alveolar) of similar severity for S-BPD and NS-BPD; and (3) even though on histological examination there are minimal changes, RAC, MLI, and their ratio may be used to support the diagnosis of BPD and help in assessing the amount of lung damage that occurs in S-BPD.     

Effects of partial liquid ventilation on lung injury in a model of acute respiratory failure: a histologic and morphometric analysis

OBJECTIVE: To compare the histopathologic changes observed in a sheep model of oleic acid-induced acute respiratory failure during partial liquid ventilation with perflubron with gas ventilation. DESIGN: Randomized, controlled study. SETTING: Animal laboratory and pathology laboratories of a university hospital. SUBJECTS: Fourteen healthy adult sheep, weighing 64.9 +/- 6.4 kg. INTERVENTIONS: Lung injury was induced with oleic acid (0.15 mL/kg). A tracheostomy tube was inserted, along with systemic and pulmonary artery monitoring catheters. Animals were randomized to undergo either partial liquid ventilation (n = 7) or gas ventilation (n = 7). Animals underwent euthanasia at the end of the 90-min study period, after which the endotracheal tube was clamped with the lungs in expiratory hold at a positive end-expiratory pressure of 5 cm H2O. En bloc excision of the heart and lungs was performed by thoracotomy. Perfusion of the isolated lung vasculature with 2.5% paraformaldehyde and 0.25% glutaraldehyde in a 0.1-M phosphate buffer was performed. Histologic analysis followed. MEASUREMENTS AND MAIN RESULTS: Gas exchange increased markedly in the animals that underwent partial liquid ventilation compared with the gas-ventilated animals (PaO2 at 90 mins: gas ventilation-treatment group, 40 +/- 8 torr [5.3 +/- 1.1 kPa]; partial liquid ventilation-treatment group, 108 +/- 60 torr [14.4 +/- 8.0 kPa]; p = .004). Lung histologic analysis demonstrated a better overall diffuse alveolar damage score (partial liquid ventilation-treatment group, 12.4 +/- 1.4; gas ventilation-treatment group, 15.0 +/- 1.7; p = .01). In the partial liquid ventilation-treatment group, we observed an increase in mean alveolar diameter (partial liquid ventilation-treatment group, 82.4 +/- 2.9 microm; gas ventilation-treatment group, 67.7 x 3.9 microm; p = .0022) and a decrease in the number of alveoli per high-power field (partial liquid ventilation-treatment group, 25.7 +/- 0.9, gas ventilation-treatment group, 31.4 +/- 2.5; p = .0022), in septal wall thickness (partial liquid ventilation-treatment group, 6.0 +/- 0.6 microm; gas ventilation-treatment group, 8.3 +/- 1.0 microm; p = .0033), and in mean capillary diameter (partial liquid ventilation-treatment group, 13.0 +/- 0.8 microm; gas ventilation-treatment group, 19.9 +/- 1.4 microm; p = .0022). CONCLUSIONS: Partial liquid ventilation is associated with notable improvement in gas exchange and with a reduction in the histologic and morphologic changes observed in an oleic acid model of acute lung injury.     

Rapid reperfusion causes stress failure in ischemic rat lungs

OBJECTIVE: Rapid reperfusion may be injurious to the ischemic lung. Our aim was to confirm that slow reperfusion improves postischemic pulmonary function and to elucidate the ultrastructural changes associated with slow versus rapid reperfusion. METHODS. We used an ex vivo perfused rat lung transplant model to study the effect of slow versus rapid reperfusion on subsequent lung function and morphologic conditional. Functional assessment was performed in (1) fresh lung, slowly reperfused; (2) fresh lung, rapidly reperfused; (3) ischemic lung (4 hours at 22 degrees C), slowly reperfused; and (4) ischemic lung, rapidly reperfused. RESULTS: In group 4, the shunt fraction (P=.001), airway pressure (P=.001), and wet/dry ratio (P=.01) were significantly higher than in groups 1 through 3. Light and electron microscopy of slowly reperfused ischemic lungs (n=4) appeared normal. Rapidly reperfused ischemic lungs (n=4) demonstrated massive alveolar edema hemorrhage, and epithelial "blebbing" by light microscopy. Electron microscopy identified the blebbing as separation of the epithelial layer from an intact basement membrane by edema fluid. The epithelial layer was disrupted in numerous locations. Complete disruption of all layers of the blood-gas barrier was occasionally present. CONCLUSION: Rapid reperfusion of the ischemic lung is an important contributing factor to reperfusion lung injury resulting in mechanical stress failure of the alveolar/capillary barrier. Gradual reintroduction of blood flow to the ischemic lung improves oxygenation.     

A corticotropin-releasing hormone type I receptor antagonist delays parturition in sheep

In sheep, corticotropin-releasing hormone (CRH) can stimulate the fetal release of ACTH to produce a cortisol surge which leads to the onset of parturition. We tested the hypothesis that fetal CRH is a primary factor in the onset of parturition in sheep by using a Type I CRH receptor antagonist, antalarmin, to block the endogenous action of CRH. Pregnant ewes were cannulated at 130-135 days of gestation. Five catheters were placed into the amniotic sac, fetal femoral artery, fetal tarsal vein, maternal jugular vein and carotid artery. After 5 days' recovery, blood samples from maternal and fetal vessels were collected at the following times: a day before the start of infusion, at [-1, 0, 1, 2, 4, 8 and 24]h, on the first day of infusion, and thereafter daily throughout a 10-day infusion. Animals (n=6 per group) received infusions into a fetal vein of either a vehicle comprising 1:1 mixture of ethanol and polyethoxylated castor oil (Cremophor EL) or antalarmin (50 g/L) in the vehicle at a rate of 0.3 mL/h. The plasma samples were assayed for ACTH and cortisol using commercial RIA kits. Fetuses infused with vehicle delivered at a mean gestational age of 141.8 +/- 0.9 days compared with antalarmin-infused sheep at 148.8 +/- 1.6 days (P = 0.0036, unpaired Student's t-test). Fetal ACTH and cortisol did not change in the antalarmin-infused sheep after 3 days' infusion compared to significant increases in vehicle-infused sheep (P=0.004 and P = 0.016 respectively, ANOVA). These data show that CRH receptor antagonism in the fetus can delay the onset of parturition. It supports the hypothesis that hypothalamic CRH drives fetal production of ACTH and is essential for the onset of parturition triggered by a surge in fetal cortisol.     

Placebo-controlled comparison between a single dose and a multidose of betamethasone in accelerating lung maturation of mice offspring

OBJECTIVE: Our purpose was to determine, in a placebo-controlled manner with a mouse model, whether a multidose of betamethasone is more beneficial than a single dose in accelerating fetal lung maturation. STUDY DESIGN: Ninety gravid CD-1 mice were randomly assigned to 1 of 3 groups (n = 30) to receive either a placebo (0.25 mL subcutaneously) or betamethasone (0.1 mg subcutaneously) as a single dose on gestational day 14 or as a multidose twice daily on gestational day 14 and 15. Ten pregnancies in each group were terminated at gestational day 16.5 to observe the neonatal breathing pattern (scale 0 to 5; 5 is unlabored breathing) and the lung histologic findings (scale 0 to 5; 5 is alveolar budding). The lungs of the offspring belonging to the remaining 20 pregnancies in each group were removed and weighed at postnatal day 1, 3, 5, or 120. RESULTS: Fetuses exposed to a multidose of betamethasone displayed a higher breathing score at gestational day 16.5 than either to a single dose or to the placebo (mean score 4.6 vs 3.8 or 1.3; P <. 001). Alveolar development was greater after exposure to a multidose of betamethasone than after a single dose or after a placebo (mean score 4.4 vs 3.5 or 1.6; P <.001). The lung weights at gestational day 16.5 were less after a multidose of betamethasone than after a single dose of either betamethasone or a placebo (18.3 +/- 1.0 g vs 21.4 +/- 1.3 g or 23.3 +/- 1.3 g; P <.02). The lung/body weight ratio was similarly affected. This reduced weight of the lungs persisted postnatally into adulthood. CONCLUSIONS: With a CD-1 mouse model, a multidose of antenatal betamethasone accelerated fetal lung maturation more than after a single dose but was accompanied with a decrease in lung weight that persisted into adulthood.     

Effect of alveolar lining material on phagocytic and bactericidal activity of lung macrophages against Staphylococcus aureau

Unstimulated rabbits were sacrificed and their lungs washed with heparinized saline. After alveolar macrophages were harvested, the cell-free lavage fluid was centrifuged at 47,000 X g to recover a small, whitish, surface-active pellet (F fraction.) The supernatant was concentrated 15-fold by vacuum dialysis (P fraction). Alveolar macrophages in a serum-free system were challenged with radiolabeled (32P) Staphylococcus aureus preincubated in either balanced salt solution or F or P fraction. A small increase in alveolar macrophage bacterial uptake occurred with P fraction-treated staphylococci. P fraction from locally immunized animals further enhanced phagocytosis. In bactericidial experiments, alveolar macrophages were allowed to phagocytize staphylococci preincubated in either balanced salt solution or F fraction. Intracellular bactericidal activity of alveolar macrophages was quantitated by lysotaphin lysis of extracellular bacteria and quantitation of viable intracellular bacteria. Enhanced lung macrophage bactericidal activity against F fraction-incubated staphylococci was noted.     

Site specificity of surfactant protein expression in airways of baboons during gestation

BACKGROUND: There are disparate reports concerning the presence of surfactant proteins in the airways of lung. The recent finding of SP-A in tracheobronchial epithelium and submucosal glands in lungs from second trimester humans has renewed interest in potential new functions of surfactant in lung biology. METHODS: In situ hybridization studies were done to determine the distribution of SP-A, SP-B, and SP-C in baboon lung specimens from 60, 90, 120, 140, 160, and 180 (term) days of gestation and adults. Lungs from gestation controls were obtained at the time of hysterotomy and adult lungs at necropsy. Riboprobes used for in situ hybridization contained the entire coding regions for human SP-A, SP-B, and SP-C. RESULTS: At 60 days, SP-C mRNA expression was evident in focal portions of primitive tubular epithelium but not bronchi. This distal pattern of SP-C mRNA expression persisted and was present in some epithelial cells of respiratory bronchioles at term. At 90 days, SP-A mRNA expression was present in the epithelium of trachea and large bronchi. SP-B mRNA expression was found in small bronchi, bronchioles, and distal tubular epithelium at 120 days of gestation. SP-A mRNA bronchiolar localization became evident at 140 days of gestation and alveolar type 2 cellular expression at 160 days of gestation. Abrupt transitions of surfactant protein expression were identified (e.g., SP-A mRNA-positive cells in the epithelium of large bronchi with adjoining SP-B mRNA expression in small bronchi and bronchioles). CONCLUSIONS: Findings in the baboon indicate that there are well-delineated sites of surfactant protein mRNA expression in bronchial and bronchiolar epithelia. mRNA expressions of SP-A and SP-B are present in both bronchial and bronchiolar epithelium but at different sites, whereas SP-C expression is seen in loci of epithelial cells in respiratory bronchioles.