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The proinflammatory stimulus of chorioamnionitis is commonly associated with preterm delivery. Women at risk of preterm delivery receive antenatal glucocorticoids to functionally mature the fetal lung. However, the effects of the combined exposures of chorioamnionitis and antenatal glucocorticoids on the fetus are poorly understood. Time-mated ewes with singleton fetuses received an intra-amniotic injection of lipopolysaccharide (LPS) either preceding or following maternal intramuscular betamethasone 7 or 14 days before delivery, and the fetuses were delivered at 120 days gestational age (GA) (term = 150 days GA). Gestation matched controls received intra-amniotic and maternal intramuscular saline. Compared with saline controls, intra-amniotic LPS increased inflammatory cells in the bronchoalveolar lavage and myeloperoxidase, Toll-like receptor 2 and 4 mRNA, PU.1, CD3, and Foxp3-positive cells in the fetal lung. LPS-induced lung maturation measured as increased airway surfactant and improved lung gas volumes. Intra-amniotic LPS-induced inflammation persisted until 14 days after exposure. Betamethasone treatment alone induced modest lung maturation but, when administered before intra-amniotic LPS, suppressed lung inflammation. Interestingly, betamethasone treatment after LPS did not counteract inflammation but enhanced lung maturation. We conclude that the order of exposures of intra-amniotic LPS or maternal betamethasone had large effects on fetal lung inflammation and maturation.

Objective: The objective of the study was to assess the efficacy of maternal betamethasone for improving preterm lung function in the presence of inflammation induced by amniotic fluid Ureaplasma colonization., Study Design: Ewes bearing single fetuses were randomized to receive an intraamniotic injection of Ureaplasma parvum (serovar 6; 2 x 10(7) colony-forming units) or vehicle at 86 +/- 2 days of pregnancy (mean +/- SD: term is 150 days), followed by maternal intramuscular betamethasone (0.5 mg/kg) or saline, either 2 or 7 days before delivery of lambs at 123 +/- 1 d., Results: Amniotic fluid interleukin-8 was elevated by ureaplasmas (P = .049) but unaffected by betamethasone. Lung inflammation induced by ureaplasmas was not affected by betamethasone. Lung compliance was increased by Ureaplasma colonization (P = .009) and betamethasone (P = .042), and effects were additive. Lung surfactant was increased by Ureaplasma colonization (P < .001) and betamethasone 7 days (P = .001), but not 2 days, before delivery., Conclusion: Inflammation improves preterm lung function because of increases in surfactant. Antenatal corticosteroids further augment lung function through an apparently independent mechanism.

Objective: We evaluated lung maturation responses to the mixture of betamethasone phosphate (Beta-PO4) + betamethasone acetate (Beta-Ac) in comparison to Beta-PO4 or Beta-Ac in fetal sheep., Study Design: Ewes carrying singleton pregnancies at 122 days of gestation were randomized to single doses of 0.5 mg/kg Beta-PO4 + Beta-Ac, 0.25 mg/kg Beta-PO4, 0.5 mg/kg Beta-PO4, or 0.25 mg/kg Beta-Ac given 48 hours before delivery. These treatments were compared with saline placebo and 2 doses of 0.5 mg/kg Beta-PO4 + Beta-Ac that were given 48 and 24 hours before delivery. Fetal lung maturation was evaluated., Results: The 2 doses of the Beta-PO4 + Beta-Ac mixture gave the best lung maturation. Single doses of the Beta-PO4 + Beta-Ac mixture and Beta-Ac alone also induced lung maturation. There were no consistent responses to either dose of Beta-PO4., Conclusion: Beta-PO4 alone is ineffective with the dosing schedule used; Beta-Ac can induce lung maturation. However, the best responses result from the mixture of Beta-PO4 + Beta-Ac.

Corticosteroids are routinely administered to women at risk for preterm delivery to induce fetal lung maturation. Antenatal corticosteroids have immunomodulatory effects on fetal immune cells that are poorly understood. We hypothesized that maternal betamethasone would alter in fetal monocytes both the initiation of inflammation in response to pro-inflammatory stimuli and the resolution of inflammation by phagocytosis of apoptotic neutrophils. Preterm lambs at 124 d gestation were delivered 15 h, 1 d, 2 d, or 7 d after 0.5 mg/kg maternal intramuscular betamethasone. Monocytes from cord blood were isolated and cultured and results were compared with monocytes from preterm lambs exposed to maternal saline or monocytes from adult sheep. Phagocytosis of Escherichia coli was not changed, however, phagocytosis of apoptotic neutrophils was low in fetal monocytes but increased after 7 d exposure to maternal betamethasone to the level found in adult monocytes. Hydrogen peroxide production after endotoxin stimulus was significantly reduced to 7.1 +/- 2.2 micromol at 5 h, 8.7 +/- 2.9 micromol at 24 h, and 4.1 +/- 1.9 micromol at 48 h versus 16.4 +/- 3.6 micromol in control animals; at 7 d, the hydrogen peroxide production increased to 74.3 +/- 19.7 micromol (p < 0.05, per 10(6) monocytes). IL-6 production was reduced at 15 h after maternal betamethasone but at no other time point. Maternal betamethasone initially suppressed several fetal monocyte functions, however, at 7 d, measurements of initiation and resolution of inflammation were increased to levels similar to monocytes from adult sheep. The time-dependent changes in maternal betamethasone modulation of the responses of fetal monocytes may influence immune function of the preterm lamb after delivery.

Objective: Intra-amniotic administration of endotoxin in sheep is a model of subclinical chorioamnionitis. Intrauterine inflammation alters lung development to improve postnatal lung function and may predispose the infant to lung and brain injury. We describe the effects of intra-amniotic endotoxin on cytokines and white cell responses in the membranes and amniotic fluid and investigate the hypothesis that betamethasone treatment suppresses these responses., Study Design: Pregnant ewes were allocated at random to receive either intra-amniotic saline solution (control animals), maternal intramuscular betamethasone, intra-amniotic endotoxin by ultrasound guidance (10 mg Escherichia coli 055:B5), or a combination of the betamethasone and endotoxin treatments. Lambs were delivered abdominally at 110 to 125 days of gestation at time points that ranged from 2 hours to 15 days after treatment., Results: When compared with saline solution-injected control animals, the intra-amniotic injection of endotoxin increased white cell counts in amniotic fluid. Levels of interleukin-8, but not interleukin-6, were significantly increased in amniotic fluid from 5 hours to 15 days after intra-amniotic endotoxin injection, and interleukin-8 levels were not decreased by concurrent treatment with betamethasone. After endotoxin treatment, interleukin-1beta and interleukin-8 messenger RNA were expressed in chorion, and interleukin-6 messenger RNA expression was localized to chorionic blood vessel epithelium. The half-life of endotoxin in the amniotic fluid was 1.7 days, and levels remained measurable 15 days after injection., Conclusion: These findings confirm that the fetus can survive within amniotic fluid that contains endotoxin, white cells, and cytokines for periods of weeks or more. Betamethasone treatment can suppress the initial inflammation in the amnion-chorion, but interleukin-8 levels and inflammatory cells in amniotic fluid were not suppressed 5 and 15 days after betamethasone treatment, presumably because of the slow clearance of bioactive endotoxin from the amniotic fluid.

Objective: The purpose of this study was to compare efficacy on fetal lung maturation of intra-amniotic betamethasone or budesonide with the efficacy of maternal intramuscular betamethasone., Study Design: Pregnant ewes received intra-amniotic betamethasone (0.5 mg/kg or 2 mg/kg fetal weight), intra-amniotic budesonide (0.5 mg/kg or 2 mg/kg), maternal intramuscular betamethasone (0.5 mg/kg maternal weight), intra-amniotic saline solution, or maternal saline solution. Lambs were delivered 2 or 7 days later, at 124 days of gestation for measurement of respiratory system compliance, ventilatory efficiency index, and surfactant levels., Results: Lung function increased 2 days after maternal betamethasone, intra-amniotic betamethasone (2 mg/kg), and intra-amniotic budesonide (2 mg/kg) administration and 7 days after maternal betamethasone or intra-amniotic budesonide (2.0 mg/kg) administration. Lung function was not improved 7 days after intra-amniotic betamethasone (2.0 mg/kg) administration or 2 days after intra-amniotic betamethasone (0.5 mg/kg) or intra-amniotic budesonide (0.5 mg/kg) administration. Intra-amniotic corticosteroid administration increased fetal death and respiratory morbidity., Conclusion: Intra-amniotic corticosteroid administration improved preterm lung function, but the associated morbidity and mortality rates suggest that they are not suitable for clinical use.

Antenatal betamethasone (Beta) is widely used in women with asymptomatic chorioamnionitis at risk for preterm delivery, but its effects on fetal inflammation are unstudied. Groups of ewes at 109 +/- 1 days of gestation received the following treatments: intra-amniotic (IA) saline (control), 0.5 mg/kg intramuscular Beta, 10 mg IA endotoxin (Endo), and Beta + 2 h later Endo (Beta + Endo). Beta suppressed Endo-induced lung inflammation at 1 day. However, compared with Endo 5 days after treatment, Beta + Endo lambs had increased alveolar neutrophils, proinflammatory cytokine mRNA expression, and serum amyloid A3 (SAA3) mRNA expression. IL-1beta mRNA expression was localized to the inflammatory cells, whereas SAA3 mRNA expression was induced in the bronchial epithelium and the inflammatory cells. Compared with Endo, Beta + Endo lambs had increased lung inflammation but equivalent lung volumes 15 days after treatment. The late increase in inflammation in the Beta + Endo animals suggests that glucocorticoids impair the ability of the preterm lung to downregulate Endo-induced inflammation after fetal clearance of the glucocorticoids. These results have implications for lung inflammation and bronchopulmonary dysplasia in preterm infants exposed to chorioamnionitis and maternal glucocorticoids.

Objective: Renal and cardiovascular function improves in preterm newborn lambs after a single prenatal betamethasone treatment. We hypothesized that multiple betamethasone exposures would further improve renal and cardiovascular adaptation., Study Design: Pregnant ewes were chosen randomly to receive saline solution, one dose of 0.5 mg/kg betamethasone at 104 days of gestation, or three doses of 0.5 mg/kg betamethasone at 104, 111, and 118 days of gestation. Lambs were delivered at 125 days of gestation (preterm) or 145 days of gestation (term). Renal and cardiovascular responses to phenylephrine were evaluated at 2 hours of age., Results: The preterm single and multiple betamethasone-treated lambs comparably increased glomerular filtration rate, urinary flow and osmolar clearance, and sodium excretion in response to phenylephrine. Term responses were similar and not influenced by betamethasone exposure., Conclusion: Multiple courses of betamethasone do not further improve renal and cardiovascular responses from a single betamethasone dose. Renal and cardiovascular function at term is not affected by early prenatal betamethasone exposure.

Objectives: We asked whether maternal or fetal cortisol treatments induced fetal lung maturation and growth restriction compared with betamethasone and whether medroxyprogesterone (MPA) influenced lung maturation., Study Design: Pregnant sheep were randomized to receive MPA or saline solution at 100 days of gestation. At 117 days of pregnancy, ewes were randomized to receive maternal or fetal treatments with 0.5 mg/kg betamethasone, four injections of hydrocortisone given over 4.5 hours or saline solution. Body weight and lung maturation were evaluated at 125 days., Results: Maternal betamethasone decreased in birth weight by 16% and induced lung maturation. Fetal cortisol or betamethasone induced only lung maturation. Maternal cortisol caused neither growth restriction nor lung maturation. MPA did not alter lung function in control lambs or in betamethasone-treated preterm lambs., Conclusions: Maternal cortisol treatments had no apparent effects on the fetus, suggesting that growth restriction caused by betamethasone may result from unidentified effects on the maternal-placental unit.

Antenatal glucocorticoids are thought to be less effective when delivery occurs more than 7 d after initiation of treatment; therefore, repeat courses are often administered. We examined lung structure after single or repetitive antenatal glucocorticoid injections in fetal sheep. Pregnant ewes received single or repetitive doses of 0.5 mg/kg betamethasone at 7-d intervals by maternal or fetal injection, beginning at D104 or D114 with delivery at D125, D135, or D146 gestation (term = 150 d). Changes in lung structure were more pronounced after repetitive versus single injections. Repetitive fetal or maternal injections beginning at D104 (delivery at D125) resulted in comparable structural changes: alveolar volume increased by 50 to 80%, alveolar numerical density decreased by 30 to 40%, and pleural and interlobular septal volumes decreased by as much as 70%. Similar changes were seen in animals delivered at D135 after repetitive maternal injections beginning at D114. There were no structural differences between control and repetitive betamethasone animals when delivery was delayed until D146, indicating that betamethasone induced structural changes were reversible.

In utero inflammation may accelerate fetal lung maturation but may also play a role in the pathogenesis of chronic lung disease. We examined the impact of endotoxin, a potent proinflammatory stimulus, on structural and functional maturation of preterm sheep lungs. Date bred ewes received 20 mg Escherichia coli endotoxin or saline by ultrasound guided intra-amniotic injection at 119 d gestation. A comparison group of animals received 0.5 mg/kg betamethasone, a known maturational agent, at 118 d gestation. Lambs were delivered by cesarean section at 125 d (term = 150 d) and ventilated for 40 min. Lung function data are reported elsewhere. Total and differential white cell counts were performed on amniotic fluid and fetal lung fluid samples. Morphometric analyses were performed on inflation fixed right upper lobes. Total cell count increased slightly but not significantly in both amniotic fluid and fetal lung fluid. Both endotoxin and betamethasone had similar effects on alveolarization: average alveolar volume increased by approximately 20% and total alveolar number decreased by almost 30%. Both treatments led to thinning of alveolar walls, although this was statistically significant in the betamethasone-treated group only. Although antenatal endotoxin leads to striking improvements in postnatal lung function, this may be at the expense of normal alveolar development.

During a series of studies investigating the maturational response to antenatal glucocorticoids, we observed that 70% of lambs delivered at 128 d gestation (term = 150 d), 24 h after a single injection of 0.5 mg/kg betamethasone or betamethasone + L-thyroxine (15 microgram/kg), developed pulmonary interstitial emphysema (PIE), compared with less than 5% of control animals or animals delivered 48 h or 7 d after hormone treatment. This study examined whether the lungs of animals that developed PIE were functionally or structurally different from those that did not. Lambs were mechanically ventilated for 40 min after cesarean section delivery. Hormone-treated animals with PIE were ventilated at similar peak inspiratory pressure (PIP) to control animals, whereas those without PIE were able to be ventilated at significantly lower PIP. Volume-dependent elastance (E2V), which provides an index of overdistension during mechanical ventilation, was lowest in PIE animals. Alveolar architecture was distorted in almost all ventilated animals, the most severe distortion occurring in PIE animals. There was no evidence of excessive alveolar wall thinning in PIE animals, although parenchymal collagen was 30% lower, and elastin 120% higher than in control animals. PIE was associated with structural differences, but not with overventilation.

Glucocorticoids are administered for preterm labor to improve postnatal adaptation. We assessed the effect of antenatal betamethasone (Beta) treatment on preterm newborn lamb neuroendocrine [catecholamine, arginine vasopressin (AVP)] and endocrine [triiodothyronine (T(3)), ANG II, and atrial natriuretic factor (ANF)] adaptive responses following delivery and a hypoxic challenge. Beta treatment included direct fetal injection at 0.2 (F(0.2); n = 8) or 0.5 (F(0.5); n = 7) mg/kg estimated fetal body weight or maternal injection with 0.2 (n = 8) or 0.5 mg/kg (M(0.5); n = 8). Control animals received fetal and maternal intramuscular injections of saline (n = 8). After 24 h, lambs were delivered by cesarean section, surfactant treated, and ventilated for 4 h. Relative to the control lambs, 3 h after delivery, there was a marked suppression of plasma cortisol, epinephrine, norepinephrine, and ANG II levels and elevated plasma T(3) and ANF levels, systolic blood pressure, and left ventricular contractility (dP/dt; F(0.5) and M(0.5)) values in F(0.5) and both maternal Beta-treated groups. However, Beta treatment augmented the cardiac output, cortisol, norepinephrine, AVP, and ANF responses to 20 min of hypoxia (PO(2) = 25-30 mmHg). We concluded that short-term (24 h) antenatal glucocorticoid exposure 1) alters preterm newborn postnatal blood pressure regulation in the face of marked depression of plasma cortisol, catecholamine, and ANG II levels and 2) augments the postnatal neuroendocrine and endocrine responses to a hypoxic challenge.

We assessed renal and cardiovascular function in preterm newborn lambs after antenatal glucocorticoid exposure. Pregnant ewes were randomly assigned to receive betamethasone or saline via either direct fetal or maternal injection at 122 d gestation. Lambs were delivered 15 h later, and cardiovascular and renal function was assessed. Two hours after delivery, baseline urine flow, urinary sodium excretion, and urinary osmolar clearance were similar in all groups. Volume expansion (saline, 2.5% of body weight, for 10 min) increased values for urine flow (0.23 +/- 0.04 to 0.58 +/- 0.09 mL x min(-1) x kg(-1)), urinary sodium excretion (29.7 +/- 5.8 to 76.2 +/- 12.3 microEq x min(-1) x kg(-1)), and osmolar clearance (12.2 +/- 1.2 to 24.3 +/- 1.6 mL/100 mL GFR) in the fetal group. Increases in urine values were also observed in the maternal group, but control values did not change significantly. Mean arterial pressure was increased in both betamethasone-treated groups relative to controls. Short-term antenatal betamethasone exposure 1) augments preterm newborn kidney adaptive responses to acute volume expansion, and 2) increases postnatal blood pressure in preterm newborn lambs.

Objective: We hypothesized that the proinflammatory response to intra-amniotic endotoxin would induce lung maturation in preterm lambs., Study Design: Ewes were randomly assigned to receive 20 mg Escherichia coli endotoxin by intra-amniotic injection, maternal betamethasone (0.5 mg/kg), or sodium chloride solution. Preterm lambs were delivered at 125 days' gestation and underwent ventilation to assess lung function. Lung gas volume, surfactant concentrations, and inflammation were subsequently evaluated, with data analyzed by analysis of variance., Results: Fetal endotoxin exposure 6 days before delivery increased compliance by 59%, increased lung gas volume 2.3-fold, increased concentrations of surfactant lipids, increased surfactant A and B protein levels, and increased messenger ribonucleic acid expressions for surfactant proteins (all P <.01, vs control group). Betamethasone exposure resulted in less consistent effects. White blood cell counts were increased in fetal membranes and lungs after endotoxin exposure, but there was no severe inflammation., Conclusion: A single fetal exposure to endotoxin resulted in large improvements in postnatal lung function and increases in surfactant concentrations after preterm delivery. These effects were qualitatively larger than those achieved with betamethasone.

Glucocorticoid treatment increases content of surfactant protein (SP) A and SP-B in lung tissue and lavage fluid of preterm lambs. To investigate this process, we determined the ontogeny and glucocorticoid induction of SP mRNAs. In separate treatment protocols, each with its own controls, sheep were injected with betamethasone 15 h, 48 h, or weekly for 1-4 doses before preterm delivery. Using ovine SP cDNAs, we found an increase equal to or more than threefold in basal levels of all three SP mRNAs between 125 days and term. After betamethasone treatment, SP-B and SP-C mRNA levels increased by 15 h and all SP mRNAs were elevated after 24 h (>/=2-fold); mRNA levels in fetuses delivered 1-3 wk after betamethasone were not different from control. We conclude that in vivo betamethasone rapidly induces a coordinated increase in SP mRNAs, which is fully reversible within 7 days despite repetitive doses of betamethasone. Similar increases in mRNA and protein contents for SP-A and SP-B suggest that glucocorticoid regulation of these SPs in vivo is primarily pretranslational.

We studied the synthesis of surfactant and the effect of prenatal betamethasone treatment in vivo in very preterm baboons. Ten pregnant baboons were randomized to receive either betamethasone (beta) or saline (control) 48 and 24 h before preterm delivery. The newborn baboons were intubated, treated with surfactant, and ventilated for 6 d. They received a 24-h infusion with the stable isotope [U-(13)C]glucose as precursor for the synthesis of palmitic acid in surfactant phosphatidylcholine (PC). Palmitic acid in surfactant PC became enriched 27 +/- 2 h after the start of the isotope infusion and was maximally enriched at 100 +/- 4 h. The fractional synthesis rate of PC palmitate in the beta group (1.5 +/- 0.2%/d) was increased by 129% above control (0.7 +/- 0.1%/d) (p < 0.02, Mann- Whitney U test). The absolute synthesis rate of PC in the beta group [1.6 +/- 0.3 micromol/kg/d] was increased by 128% above controls [0.7 +/- 0.2 micromol/kg/d] (p < 0.02). These data show that the synthesis of endogenous surfactant from plasma glucose as precursor is a slow process. It is shown, for the first time in vivo, that prenatal glucocorticosteroids stimulate the synthesis of surfactant PC in the very premature baboon.

This study examined whether the improvement in lung function after prenatal hormone exposure coincided with changes in lung morphometry or in collagen and elastin content. Fetal lambs received a single intramuscular injection of betamethasone (0.5 mg/kg) plus L-thyroxine (T4) (15 micrograms/kg) or vehicle control 48 h before delivery at 121, 128, or 135 d gestational age (d 121, d 128, d 135, term = 150 d). T4 was administered in conjunction with betamethasone in an attempt to enhance the maturational response. The right-upper lobes were instillation fixed at 30 cm H2O by Karnovsky's fixative after a 40-min period of mechanical ventilation. A number of significant changes occurred between d 121 and d 135 in control animals: alveolar airspace volume increased by 270%; despite a 40% reduction in alveolar septal thickness, alveolar septal volume did not change appreciably, suggesting a "redistribution" of septal tissue into the formation of secondary alveolar septa, which doubled in number; and both parenchymal collagen and elastin volume increased significantly, whereas pleural collagen and elastin volume did not change. In contrast to the changes seen in control animals, exposure to betamethasone plus T4 led to alveolar septal thinning at each gestational age without an associated increase in secondary septal number, a 40% decrease in alveolar septal volume, and a proportionate reduction in parenchymal elastin at d 121. Although attenuation of alveolar septa coincides with redistribution of septal tissue into the formation of secondary septa during normal maturation, exposure to betamethasone plus T4 promotes thinning of alveolar septa in the absence of secondary septal formation, which results in a loss of alveolar septal tissue.

Background: Although single courses of antenatal glucocorticoids decrease respiratory distress syndrome and mortality, repetitive courses of antenatal glucocorticoids are being given to women at risk of preterm delivery without evidence of benefit or appreciation of potential risks., Objectives: To evaluate the effects of single and repetitive antenatal glucocorticoid exposures on fetal growth and postnatal lung function in sheep., Methods: Pregnant ewes were randomized to three protocols that included one or three doses (at 7-day intervals) of 0.5 mg/kg of betamethasone (beta) given to the ewe or fetus beginning at gestations ranging from 104 to 128 days' gestation with delivery at 125, 135, and 146 days' gestation. Postnatal assessments included measurements of gas exchange, compliance, ventilation efficiency, static lung volume, and lung tissue and alveolar wash saturated phosphatidylcholine., Results: Single or repetitive maternal beta but not fetal beta caused fetal growth retardation at delivery at 125, 135, and 146 days' gestation. Single-dose fetal beta had no effect on postnatal lung function whereas single-dose maternal beta significantly increased compliance, lung volume, and tissue and alveolar surfactant after preterm delivery. Although three-dose fetal beta improved all indicators of postnatal lung function, three-dose maternal beta resulted in larger responses. The added benefits of repetitive beta relative to a single-dose beta on postnatal lung function after preterm delivery were not as great when therapy was begun later in gestation. Postnatal lung function after delivery at 146 days' gestation (term is 150 days) was improved after repetitive maternal beta at early gestational age., Conclusions: In sheep, single or repetitive maternal beta causes growth retardation from 104 to 121 days' gestation and the growth retardation persists to term. In contrast, single or repetitive fetal beta does not cause fetal growth retardation and is less potent at improving postnatal lung function and increasing surfactant pools. There are potential benefits as well as risks for the use of repetitive antenatal glucocorticoids. Randomized, controlled trials in humans are essential given the widespread use of repetitive courses of antenatal glucocorticoids in women at risk of preterm delivery. respiratory distress syndrome, maturation, prematurity, growth retardation, surfactant.

Objective: We evaluated the effects of single or three repeated doses of maternal betamethasone on fetal growth at preterm and term delivery in sheep., Study Design: Pregnant ewes were randomly assigned to receive one dose of 0.5 mg/kg betamethasone at 104 days' gestational age; three doses of betamethasone at 104, 111, and 118 days' gestational age; or saline for controls. Lambs were delivered at 125 days' (preterm) or at 145 days' (term) gestational age for assessments of fetal growth., Results: The single betamethasone exposure at 104 days' gestational age caused symmetric growth retardation of 11% at 125 days' gestational age and 14% at term. The three-dose exposures decreased body weights by 25% in preterm lambs and by 19% at term. Organ protein and deoxyribonucleic acid per kilogram of body weight were selectively decreased in preterm lambs. At term the decreases in organ weight, protein, and deoxyribonucleic acid were proportionate to the decreased birth weight., Conclusion: One or three doses of maternal glucocorticoids begun at an early gestational age caused symmetric growth retardation in lambs delivered prematurely, and the decreased fetal size persisted to term.

Abnormalities of premature newborn adaptation after preterm birth result in significant perinatal mortality and morbidity. We assessed the effects of short-term (24 h) fetal betamethasone exposure on preterm newborn baboon pulmonary and cardiovascular regulation and renal sodium handling during the first 24 h after birth. Male fetal baboons (Papio) (124-day gestation, term 185 days) received ultrasound-guided intramuscular injections of saline (n = 5) or betamethasone (0.5 mg/kg; n = 5). Fetuses were cesarean delivered 24 h later, treated with 100 mg/kg surfactant, and ventilated by adjusting peak inspiratory pressures to maintain PCO2 values of 35-50 mmHg for 24 h. Betamethasone- vs. saline-treated mean +/- SE newborn body weights (0.45 +/- 0.02 vs. 0.41 +/- 0.01 kg) were similar. Although prenatal betamethasone did not affect postnatal lung function (PCO2, arterial/alveolar O2 gradient, or dynamic compliance), plasma hormone (cortisol or thyroxine), or catecholamine levels, mean arterial pressure (25 +/- 1 vs. 32 +/- 1 mmHg), plasma sodium concentration (132 +/- 2 vs. 138 +/- 1 meq/l), glomerular filtration rate (0.07 +/- 0.02 vs. 0.16 +/- 0.02 ml.min-1.kg-1), and renal total sodium reabsorption (1.5 +/- 0.5 vs. 16.0 +/- 3.0 mu eq.min-1.kg-1) values were significantly lower in saline-treated than in betamethasone-treated newborns at 24 h. We conclude that despite the fact that there are no pulmonary and endocrine effects, antenatal glucocorticoid exposure alters premature newborn baboon vascular and renal glomerular function and improves sodium reabsorption after preterm delivery.

The effect of fetal gender on postnatal lung function and response to prenatal steroid exposure were examined retrospectively in a group of 115 preterm lambs. Fetuses received a single intramuscular injection of 0.5 mg/kg betamethasone alone or in conjunction with L-thyroxine 48 h before delivery at 128-d gestational age. Control animals received an equivalent volume of saline. After delivery, respiratory mechanics and blood gas parameters were recorded for 40 min. Deflation pressure volume curves were constructed in excised lungs. Right upper lobes from a randomly selected subgroup of control animals were examined morphometrically. Control (saline-treated) females were able to be ventilated at lower ventilatory pressures with equivalent tidal volumes and more efficient gas exchange. There were no gender differences in compliance, conductance, or excised lung volumes for saline-treated animals. More efficient gas exchange in females could not be explained by thinner alveolar septa or greater alveolar surface area. After hormone treatment, both males and females exhibited significant improvements in respiratory mechanics, gas exchange, and an increase in alveolar surfactant concentration. However, female exhibited a significantly greater improvement than males for compliance, conductance, excised lung volume, and arterial oxygen partial pressure. These data provide a comprehensive description of gender differences in postnatal lung function and response to steroid treatment in preterm animals, and support clinical findings of sexual dimorphism.

To assess effects of dose and duration of glucocorticoid exposure on maturation of the fetal lung, we administered single or multiple doses of betamethasone (0.5 mg/kg im) to pregnant sheep for 2 or 21 days before preterm delivery at 125 days of gestation. Lung function (compliance, lung volume at 40 cmH2O pressure, and ventilatory efficiency index) was increased after two to four weekly doses of glucocorticoid (2.5- to 4-fold increase) and after 48 h of exposure (1.4- to 2.3-fold). Total protein of lavage fluid decreased similarly with three doses, four doses, and 48 h of treatment. In lambs with long-term exposure to betamethasone, there was a similar, dose-dependent increase in concentrations of saturated phosphatidylcholine and surfactant proteins A (SP-A) and B (SP-B) (maximal 2- to 3-fold in tissue and 10- to 15-fold in lavage fluid). Levels of SP-A and SP-B were closely correlated in lavage fluid. In animals treated for 48 h, only tissue SP-B was increased (2.7-fold). We conclude that 48 h of glucocorticoid treatment improves lung function in the premature lamb without a detectable increase in lavage surfactant components and that longer exposure to antenatal glucocorticoid increases surfactant lipid and proteins in a coordinated fashion. The enhanced response with repetitive dosing indicates that the process of glucocorticoid-induced lung maturation is either reversible and/or gestational age dependent.

Prenatal glucocorticoid plus T4 treatment of fetal sheep results in improvements in oxygenation, gas exchange, lung mechanics, and lung volumes after preterm delivery. We have evaluated the morphometric changes in the lungs of lambs exposed to betamethasone and T4 48 h before preterm delivery at 121 and 135 d gestation and related those changes to the physiologic improvements in lung function. The lungs used for the morphometric studies were from lambs with postnatal physiologic responses similar to those of the entire group of lambs reported previously (16). At both 121 and 135 d gestation, lung gas volumes and fixed tissue volumes increased, the percent of collapsed (nonaerated) parenchyma decreased, and the percent of perilobular connective tissue decreased with both gestational age and prenatal hormone exposure. Alveolar size, as estimated by mean linear intercept length, did not change with gestation or hormone exposure, but there was a decrease in alveolar wall thickness with advancing gestation and at each gestation with hormone exposure. The major anatomic effect of prenatal hormone exposure was a decrease in alveolar wall thickness and an increase in aerated parenchyma, effects that were consistent with the physiologic improvements in postnatal lung function.

We evaluated the effects of multiple fetal exposures to glucocorticoids on postnatal lung function and growth. Ewes were randomized to receive 1 to 4 doses of 0.5 mg/kg betamethasone or saline placebo at 7 d intervals from 104 d to 118 d and at 124 d gestation. All lambs were delivered preterm at 125 d gestation, and postnatal lung function was evaluated. There were sequential improvements in compliance, ventilation efficiency, and lung volumes for two, three, and four doses of betamethasone. The maximal effect was a 150% increase in compliance and a 4-fold increase in lung volume after fetal exposure to four doses of betamethasone. However, birth weights decreased (15% after one dose, 19% after two doses, and 27% after three and four doses). There were no changes in lung to body weight ratios, lung dry to wet weight ratios, lung protein to body weight ratios, or lung hyaluronan content. Prenatal glucocorticoid exposure also altered postnatal cortisol, thyroid, and catecholamine plasma levels. Repetitive 7-d interval exposures of fetal lambs to glucocorticoids progressively enhanced postnatal lung function and resulted in growth and endocrine abnormalities.

The optimal dose, route of administration, and treatment-to-delivery interval necessary to induce beneficial extrapulmonary effects of glucocorticoids are not known. Pregnant ewes (127 days gestation) were randomized to receive maternal or fetal intramuscular injections of betamethasone (0.2 or 0.5 mg/kg body wt) or saline 24 h before cesarean delivery of their lambs. Three hours after delivery, low-dose maternal vs. control lamb mean arterial pressure [64 +/- 4 vs. 47 +/- 2 (SE) mmHg], glomerular filtration rate (1.7 +/- 0.2 vs. 0.7 +/- 0.1 ml.min-1.kg-1), and total renal sodium reabsorption (219 +/- 31 vs. 85 +/- 12 mueq.min-1.kg-1) were increased. Comparable increases were observed in the high-dose maternal and fetal groups without effects in the low-dose fetal group. This study provides the first quantitative data demonstrating that even short-term (24-h) antenatal betamethasone exposure alters preterm newborn cardiovascular and renal functions. These responses are route and dose dependent and are comparable to glucocorticoid-induced maturational effects after longer-term antenatal exposure.

Objective: We hypothesized that two doses of betamethasone administered 1 week apart would further enhance postnatal pulmonary function in preterm lambs (compared with a single dose)., Study Design: Fetal sheep (121 days' gestation) randomly received saline solution or betamethasone (0.5 mg/kg) as a single injection. Six days later fetal sheep were retreated with either saline solution or corticosteroid, and postnatal lung function was evaluated 1 day later., Results: Betamethasone improved compliance and ventilation efficiency index nearly 50%, and total lung volume increased twofold. No effects of treatment-to-delivery interval (1 vs 7 days) or corticosteroid retreatment on pulmonary function were apparent. Although surfactant pool sizes increased as a function of duration of exposure, no additional effect of corticosteroid retreatment was noted. Antenatal betamethasone increased messenger ribonucleic acid levels for the surfactant proteins A and C, and retreatment augmented surfactant protein B messenger ribonucleic acid levels but suppressed surfactant protein A and C messenger ribonucleic acid., Conclusion: Improved postnatal lung function resulting from antenatal betamethasone was not augmented by retreatment.

We asked whether a single-dose fetal treatment strategy using betamethasone plus either a long-acting beta 2 agonist (formoterol) or betamethasone plus agents that elevate intracellular cyclic adenosine monophosphate (isobutyl methylxanthine and dibutyryl-cyclic adenosine monophosphate) would augment the effects of prenatal betamethasone on postnatal lung function. Preterm lambs were treated with 0.5 mg/kg beta-methasone or betamethasone plus the other agents and delivered 48 h after treatment. The postnatal lung function as assessed by compliance, ventilatory efficiency, and lung volumes at 40 min of age was improved by prenatal betamethasone and improved further by combination treatment, although the augmented responses were not significantly greater than with betamethasone alone. Fatty acid synthase protein and enzymatic activity were not increased by betamethasone or combined treatments, in contrast to responses reported for other animal models. There were no effects of glucocorticoids or the combined treatments on surfactant. Stimulation of the beta 2 agonist system did not augment postnatal lung function significantly above that noted for betamethasone alone with the agents, doses, and duration of exposures tested.

Unlabelled: These studies determined the effects of fetal treatment with betamethasone alone, or in combination with thyroid hormone (thyroxine; T4), on postnatal renal and endocrine adaptations in preterm newborn lambs. Ovine fetuses (126 d of gestation; term = 150 d) received single, ultrasound-guided intramuscular injections of saline, 0.5 mg/kg betamethasone (Celestone Soluspan, or 0.5 mg/kg betamethasone plus 60 micrograms/kg T4. After 48 h, lambs were delivered, treated with surfactant (Survanta, 100 mg/kg), and ventilated for 3 h. Due to maintained urine flow in the betamethasone-treated animals and a significant decrease in the saline group, betamethasone versus saline urine flow values (0.11 +/- 0.03 versus 0.03 +/- 0.004 mL.min-1.kg-1) were significantly elevated by the end of studies. GFR (1.5 +/- 0.3 versus 0.8 +/- 0.2 mL.min-1.kg-1) and mean blood pressure (61 +/- 4 versus 42 +/- 3 mm Hg) values also were higher in the betamethasone-treated animals. Although renal blood flow, renal plasma flow, and fractional sodium excretion rates did not differ, betamethasone versus saline values for the filtration fraction (11.9 +/- 1.5 versus 7.4 +/- 1.5%) and total sodium reabsorption (196 +/- 38 versus 81 +/- 16 microEq.min-1.kg-1) were increased. Betamethasone versus saline treatment also was associated with significant reductions in plasma angiotensin II (125 +/- 23 versus 550 +/- 140 pg/mL) and AVP (116 +/- 19 versus 230 +/- 77 pg/mL) levels. Overall, the effects of combined betamethasone + T4 treatment were similar to the effects of betamethasone alone., Conclusions: 1) fetal betamethasone injection 48 h before delivery stabilizes GFR and significantly alters endocrine function in preterm newborn lambs, and 2) the addition of T4 does not augment betamethasone-induced renal and endocrine responses.

Objectives: Although antenatal corticosteroids improve outcomes for preterm newborns, negative effects could result if preterm delivery does not occur. We investigated whether betamethasone treatment of preterm fetal sheep would alter cardiovascular, renal, and lung function after delivery at term., Methods: Preterm fetal lambs were randomized at 126-128 days' gestation to receive single doses of saline (n = 6) or 0.5 mg/kg betamethasone (n = 7) by ultrasound-guided fetal intramuscular injection. The lambs were delivered by cesarean at term, 20 days after fetal treatment, then ventilated for 4 hours to evaluate lung, cardiovascular, renal, and endocrine newborn adaptive responses, as well as responses to mild hypoxia., Results: Body and organ weights (brain, lung, heart, kidney, adrenal) were similar in the two groups. Values for blood gases and pH, mean arterial pressures, heart rates, glomerular filtration rates, renal osmolar clearance, and plasma cortisol, angiotensin II, epinephrine, and norepinephrine levels were similar between groups for 3 hours after delivery and before hypoxia. A 20-minute period of mild hypoxia resulted in increases in catecholamines, arginine vasopressin, and atrial natruretic factor in both betamethasone-treated and control lambs. However, hypoxia did not alter cardiovascular or lung function in either group. After reversal of hypoxia, measured physiologic parameters did not differ between groups. Kidney Na, K-adenosine triphosphatase activity was significantly higher for the betamethasone-treated lambs., Conclusion: Preterm fetal betamethasone administration does not alter neonatal pulmonary, cardiovascular, renal, or endocrine physiology after term delivery or in response to mild hypoxia.

Although administration of exogenous corticosteroids accelerates the late gestational rise in fetal rat and lamb lung antioxidant enzyme activity, the effect of dosing intervals on these responses remains uncertain. We studied the persistence and efficacy of the antioxidant response in fetal lamb lung to a single fetal dose of corticosteroids injected between 121 and 127 days gestational age. Fetal lambs received 0.5 mg/kg of betamethasone (n = 35) or saline (n = 26) by fetal intramuscular injection 24 h, 48 h, 4 days, or 7 days before preterm delivery at 128 days gestation (term = 150 days). After delivery, the lambs were ventilated for 40 min and killed. Total superoxide dismutase, catalase, glutathione peroxidase activities, and lipid hydroperoxide levels were measured, using homogenized lung. The saline-injected controls were similar at all time points. Lung antioxidant enzyme activity was consistently higher and lipid hydroperoxide presence was lower in the betamethasone-treated groups. We conclude that the positive effect of a single fetal dose of betamethasone on lung antioxidant enzyme activity occurs within 24 h after exposure, persists over a period of 7 days without a major change in the magnitude of the response, and leads to a reduction in lipid hydroperoxide formation during immediate postdelivery oxygen exposure.

Objective: We hypothesized that fetal betamethasone exposure for < 24 hours would improve postnatal lung function in preterm lambs., Study Design: Singleton fetal sheep were randomized to receive by ultrasonographically guided fetal injections of 0.5 mg/kg betamethasone or saline solution either 8 or 15 hours before preterm delivery and postnatal assessment of lung function., Results: After the 15-hour fetal treatment-to-delivery interval, betamethasone-treated lambs had twofold improvement in compliance and lung volumes, a fourfold to fivefold decrease in edema index, and higher blood pressures than saline solution-treated lambs. Postnatal lung function or lung volumes did not improve for the 8-hour treatment-to-delivery interval, although betamethasone decreased the pulmonary edema and increased the postnatal blood pressure., Conclusions: The minimal interval from fetal exposure to corticosteroids to delivery for improved postnatal lung function was between 8 and 15 hours. Corticosteroid effects on pulmonary edema and blood pressure occurred within 8 hours.

A single combined intramuscular dose of betamethasone and l-thyroxine (T4) or placebo was injected into the shoulder of fetal lambs 48 hours prior to delivery at days 121 (n = 14), 128 (n = 25) or 135 (n = 20) of gestation. Respiratory mechanics were calculated using multiple linear regression analysis. Both respiratory system resistance (RRS) and elastance (ERS) decreased approximately 4 fold between gestational days 121 (D121) and 135 (D135). Both variables were also reduced by hormone treatment. Reduction in ERS was due to a reduction in both lung (EL) and chest wall (EW) components. In absolute terms EW decreased with gestational age; however, EW as a proportion of total elastance (% EW) increased. Inclusion of a volume-dependent elastance term in the multiple linear regression model enabled us to separate total elastance into volume-independent (E1) and volume-dependent (E2V) components. E1 decreased almost 8-fold compared with only a 2.5-fold fall in E2V between D121 and D135. %E2, the proportion of ERS which is volume-dependent and which provides an index of overventilation, doubled over this time period. Hormone treatment affected E1 and E2V components equally hence %E2 was not altered. Both excised lung volume and end expiratory alveolar volume increased with gestational age and with treatment. The response to treatment was qualitatively similar at each of the gestational ages examined, however, for all mechanics variables, except resistance and E1, the magnitude of response to treatment was significantly smaller in D135 animals compared with other age groups.

Although the benefits of antenatal hormone treatment are well accepted, most studies have reported only pulmonary effects. There is evidence of beneficial cardiovascular and metabolic effects in studies using chronically catheterized animals; however because of the route of administration, the results are not directly applicable to clinical strategies. We previously demonstrated significant pulmonary effects in animals treated antenatally with a single, direct fetal, intramuscular injection of glucocorticoids. This study was performed to determine the effects of a single fetal injection of betamethasone (BETA) alone or in combination with thyroxine (T4) on cardiovascular and metabolic responses after preterm birth. Hemodynamic and metabolic responses at birth were determined in fetuses (126-d gestation; term = 150 d) treated with ultrasound-guided intramuscular injections of 0.5 mg/kg BETA (n = 7), BETA plus 60 g/kg T4 (n = 7), or saline (SAL, n = 9). After 48 h, lambs were delivered by cesarean section and studied for 3 h. BETA treatment increased mean arterial blood pressure [56 +/- 6 (SEM) versus 42 +/- 3 mm Hg], heart rate (152 +/- 5 versus 123 +/- 4 beats/min), and cardiac output (467 +/- 17 versus 349 +/- 36 mL/min/kg) versus SAL. Responses of BETA+T4-treated animals were not different from animals treated with BETA alone. Glucose and FFA were similar among all groups. The increase in catecholamine levels normally seen at birth was significantly attenuated in both the BETA and BETA+T4-treated animals. A single, intramuscular injection of glucocorticoids 48 h before delivery improves cardiovascular responses to preterm birth. This effect is not augmented by concomitant administration of T4.

We previously found that a single dose of betamethasone in combination with thyroxine given by intramuscular injection to fetal sheep 48 h before preterm delivery at 128 d gestation improved postnatal lung function. We have now asked how the combination of 0.5 mg/kg betamethasone and 15 micrograms/kg T4 given by a single fetal intramuscular injection changes lung response 48 h after treatment at 121 and 135 d gestation. At 121 d gestation the fetal hormone treatment significantly improved postnatal lung function. Compliance increased by 55%, arterial PO2 increased from 39 to 215 mm Hg, PCO2 decreased from 109 to 79 mm Hg, and maximal lung volumes increased by 112%. The hormone treatment decreased the severity of the respiratory failure, although these very preterm lambs still had severe respiratory failure. At 135 d gestation, the fetal hormone treatment decreased the ventilatory pressure requirements that were needed to normalize PCO2 values from 30 to 21 cm H2O. Compliance increased by 40%, and maximal lung volumes increased by 33%. Alveolar or lung tissue, saturated phosphatidylcholine, or alveolar SP-A pool sizes did not change with hormone treatment at 135 d gestation. We conclude that fetal hormone treatment significantly improved postnatal lung function at both gestational ages, although the characteristics of the responses were different.

Effects of prenatal corticosteroid on the properties of surfactant have not previously been evaluated. A single ultrasound-guided fetal injection with 0.5 mg/kg betamethasone 48 h before delivery of preterm lambs at 134- to 135-days gestation improved oxygenation, lowered the ventilatory pressures required to maintain arterial PCO2 between 30 and 40 Torr and decreased the protein leak of albumin from the intravascular to the alveolar space. This dose of glucocorticoid did not alter surfactant-saturated phosphatidylcholine pool sizes in the airspaces of preterm lambs. However, the treatment changed the characteristics of the surfactant recovered from the ventilated preterm lambs. The in vitro conversion from heavy to light subtype surfactant decreased from 59% for the saline-treated lambs to 37% for the corticosteroid-treated lambs after 180 min of surface area cycling (P < 0.02). Surfactant from the corticosteroid-treated lambs also increased the dynamic compliance of preterm surfactant-deficient rabbits more than did surfactant from the saline-treated lambs (P < 0.05). Prenatal treatment of preterm lambs with betamethasone improved the functional characteristics of surfactant without significant effects on the alveolar surfactant pool sizes.

Objective: We determined the effect of a single direct fetal injection of corticosteroid and thyroid hormones on postnatal pulmonary function in preterm lambs., Study Design: Initially fetal sheep (126 days' gestation) randomly received saline solution, betamethasone (Celestone Soluspan, 0.5 mg/kg), betamethasone plus triiodothyronine (5 micrograms/kg), or betamethasone plus thyroxine (15 micrograms/kg) as a single injection. Forty-eight hours later (128 days' gestation) the fetuses were delivered and ventilated for 50 minutes. In a second protocol fetuses were delivered at 128 days' gestation, after only 24 hours of hormone exposure., Results: Betamethasone treatment improved compliance nearly twofold after 24 or 48 hours of exposure. Efficiency of ventilation also improved after steroid therapy; this effect was augmented 48 hours after thyroxine exposure (but not triiodothyronine). No thyroxine effect was noted after 24 hours of exposure. Maximal lung volume increased by 80% after steroid treatment and doubled in response to combination betamethasone and thyroxine therapy. Alveolar pool sizes of saturated phosphatidylcholine and surfactant protein A were comparable for all groups exposed for 48 hours., Conclusions: A single fetal exposure to betamethasone improves postnatal pulmonary function after 24 or 48 hours. Addition of thyroxine (but not triiodothyronine) augments this effect at 48 hours.

Three groups of sheep fetuses at 125 or 126 d gestational age randomly received a single ultrasound-guided intramuscular injection of saline, 0.5 mg/kg betamethasone, or 0.5 mg/kg betamethasone plus 50 micrograms/kg thyroxine (T4). Forty-eight hours later the fetuses were delivered, treated with a pulmonary surfactant preparation, and ventilated for 3 h. Corticosteroids alone and in combination with T4 increased FRC, compliance, and lung volumes, and decreased the protein leak into the airspace. Saturated phosphatidylcholine pool sizes recovered by alveolar washing were not changed after hormone treatment. To evaluate the function of surfactant recovered from the lambs in vivo, we treated preterm rabbits at 27 d gestational age with the large-aggregate surfactant from alveolar washes. Large-aggregate surfactants and the pulmonary surfactant preparation increased compliances and maximal lung volumes relative to those in untreated preterm rabbits. Large-aggregate surfactants improved compliance more than did the pulmonary surfactant preparation. We conclude that ultrasound-guided single fetal corticosteroid treatment followed by postnatal surfactant improved postnatal lung function in preterm lambs. Addition of T4 did not augment corticosteroid effects. The function of the exogenous surfactant was improved in premature lamb lungs independently of the fetal treatment modality.

We studied the effect of a single-dose, corticosteroid treatment on preterm lambs (gestational age: 128 d). A low, medium, or high betamethasone dose (0.1, 0.5, and 2.0 mg/kg) or saline control was administered directly to the fetus by ultrasound-guided intramuscular injection 48 h before delivery. A second group received either the high dose of betamethasome or saline 24 h before delivery. The lambs were delivered at 128 d gestation, anesthetized with ketamine, and ventilated for 50 min. Respiratory system elastance and resistance were measured at 10-min intervals using multiple linear regression analysis of pressure, flow, and volume. Similarly, estimates of lung mechanics were calculated from transpulmonary pressure. The viscoelastic time constant (tau) was calculated by fitting an exponential to the pressure changes occurring after occluding the airway during expiration. Excised lung volume at 40 cm H2O and lung weight were used to calculate specific elastance and resistance correcting for lung size using volume or weight, respectively. Of the 13 lambs in the 48-h high-dose betamethasone group, five developed pulmonary interstitial emphysema (PIE) as did 3 of 11 animals in the high-dose group treated 24 h before delivery. These animals were analyzed separately. The lambs receiving medium- or high-dose (24 and 48 h predelivery) betamethasone had significantly lower elastance and a trend toward lower resistance when compared with the control groups. Ten minutes after delivery, the animals that developed PIE all had elastance values comparable to that of the control animals despite corticosteroid treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Most previous studies of induced lung maturation have used fetal exposures to multiple doses of hormones, and such treatments are associated with fetal growth retardation in rodents and rabbits. This study was designed to evaluate whether single-dose maternal corticosteroid treatments could induce lung maturation without causing fetal growth retardation. Lung maturation was evaluated in 27-d gestational age rabbits by measurements of lung function after preterm delivery and ventilation. Lung function was assessed by measurements of ventilatory requirements, responses to exogenous surfactant, measurements of the recovery of intravascular albumin in the lungs, and surfactant pool sizes. As demonstrated previously, 0.1 mg/kg betamethasone (1 mg = 2.13 mumol betamethasone) given 48 and 24 h before delivery caused both growth retardation (birth weight 20% lower than controls, p < 0.01) and lung maturation (improved compliance, decreased radiolabeled albumin recoveries) despite lower alveolar saturated phosphatidylcholine pool sizes (p < 0.05 versus controls). A single dose of 0.2 mg/kg betamethasone given 48 h before delivery had an equivalent effect on birth weight as the divided doses of 0.1 mg/kg betamethasone, with the only lung maturational effect being a decrease in recovery of labeled albumin in alveolar washes (p < 0.01). A single dose of 0.1 mg/kg betamethasone given 48 h before delivery decreased birth weight by 9.4% (p < 0.01 versus control) but had no effect on any of the lung maturation indicators. Fetal lung maturation caused by maternal corticosteroid is associated with global fetal growth retardation, and a single low dose of corticosteroid can cause growth retardation without inducing lung maturation.(ABSTRACT TRUNCATED AT 250 WORDS)

Dose-response effects of corticosteroids were investigated in the preterm rabbit. Pregnant rabbits were given two doses of 0.01, 0.03, or 0.1 mg of betamethasone per kilogram every 24 hours, beginning on day 25 of gestation. Saline solution was used in a comparison treatment group. Half of the newborn rabbits received supplemental surfactant therapy after delivery via cesarean section on day 27, and all were ventilated on a ventilator-plethysmograph system for 30 minutes. The 0.01 and 0.03 mg/kg regimens had no effect on birth weight or lung function. The 0.1 mg/kg regimen resulted in fetal growth retardation and improved ventilatory measurements, gas exchange, and decreased protein accumulation in the lung, without increasing surfactant pool size. The induction of lung maturation by corticosteroids has multiple targets in the developing lung and does not exhibit a linear dose response.

The dose-response effect of thyrotropin-releasing hormone in enhancing pulmonary maturation was investigated with six dosing regimens. Pregnant does received thyrotropin-releasing hormone (5, 10, or 50 micrograms/kg every 12 hours for four doses or one dose of 20 micrograms/kg) in conjunction with betamethasone beginning on day 25 of gestation, with betamethasone alone or saline solution used as comparison treatment groups. Half of the newborn rabbits received supplemental surfactant therapy after delivery on day 27, and all were ventilated on a ventilator plethysmography system for 30 minutes. There were no differences among the four thyrotropin-releasing hormone doses in surfactant pool sizes, compliances, or proteins leak into or out of the air spaces. The groups that received multiple doses of thyrotropin-releasing hormone had significantly higher perinatal loss rates than the single-dose group. The lungs of the group treated with thyrotropin-releasing hormone plus steroid and the rabbits treated only with steroid were more compliant than the controls without surfactant therapy, and showed significant improvements in protein leak. The addition of thyrotropin-releasing hormone to betamethasone improved several of the protein leak measurements compared with use of betamethasone alone. These results question the necessity of multiple doses of thyrotropin-releasing hormone to induce pulmonary maturation, especially when the higher perinatal mortality and the theoretical long-term effects of fetal hyperthyroidism on thyroid axis function are considered.

Pregnant rabbits received bethamethasone (0.05, 0.2, 0.4, or 0.5 mg.kg-1.day-1) or vehicle control for 2 days before delivery of fetuses at 27 days gestation to evaluate dose-related effects on surfactant pool sizes with and without ventilation, pressure-volume measurements, lung protein leaks, and precursor incorporation into lung saturated phosphatidylcholine (PC). Alveolar wash-saturated PC pool sizes in betamethasone-exposed fetuses were less than in controls (P less than 0.01). At higher doses, total lung saturated PC also decreased (P less than 0.01). Maximal lung volumes on pressure-volume loops were larger than controls only at the 0.4 mg.kg-1.day-1 dose (P less than 0.05). The larger maximal volumes, despite decreased saturated PC pools, indicated increased responsiveness of the steroid-treated lungs to the smaller saturated PC pool sizes. Vascular-to-alveolar iodinated albumin leak decreased with steroid treatment independently of dose (P less than 0.01). No consistent pattern of increased precursor incorporation into saturated PC by lung slices was seen. Our results indicate that, in preterm rabbits exposed to a range of maternal corticosteroid doses, the beneficial lung maturational effect of structural alterations with increased responses to endogenous saturated PC pools was maximal even at the lowest dose.

Fetal rabbits were treated with corticosteroids by maternal administration for 48 h before delivery at 27 days gestational age. Both corticosteroid-treated and control animals then received exogenous natural rabbit surfactant at birth at doses of 0-75 mg lipid/kg. After 10 min of ventilation at tidal volumes of 12-15 ml/kg, static pressure-volume measurements were made. At all surfactant doses there was a significantly higher maximal lung volume, higher dynamic compliance, and lower pressure requirement in the corticosteroid-treated than in the control rabbits (P less than 0.01). Control animals showed incremental improvements in dynamic compliances and maximal lung volumes up to a dose of 50 mg/kg, whereas corticosteroid treated animals improved to a maximum at the low dose of 15 mg/kg (P less than 0.01). However, surface tension as assessed by lung stability index improved with increasing surfactant dose but was not significantly different between corticosteroid-treated and control animals at a given dose. The results imply that maternal corticosteroid treatment potentiates surfactant replacement by a change in lung structure that is independent of surface tension effects.

Maternal corticosteroid treatments decreased lung protein leaks and increased the compliance responses to exogenous surfactant in 27-day preterm rabbits. We asked if maternal corticosteroid treatments at different gestational ages might alter these responses. Pregnant does were given 0.1 mg/kg betamethasone 48 and 24 h before study of the rabbits at 27, 28, and 29 days of gestational age and term newborns at 31 days of gestational age. Alternate rabbits at each gestation were treated with 50 mg/kg surfactant after delivery. Alveolar saturated phosphatidylcholine pool sizes increased with gestation similarly in control and corticosteroid-treated groups. Corticosteroids improved compliance relative to control values at 29 days of gestational age in animals not treated with surfactant and improved the compliance response to surfactant treatment at 27 and 28 days of gestational age. Corticosteroids decreased the leak of radiolabeled albumin to the lungs and alveolar washes at all preterm gestations with a maximum decrease to 16% of the control value at 29 days of gestation. Surfactant decreased this protein leak more effectively than did corticosteroids at the earlier gestations. There were potentially beneficial effects of corticosteroids either alone or together with surfactant at all preterm gestations studied. No protein leak or compliance effects of either treatment were noted in the term newborns.

The relationship between alveolar saturated phosphatidylcholine pool size and compliance was evaluated in control and maternal corticosteroid-treated 27-, 28-, and 29-day gestational age preterm ventilated rabbits. Surfactant pool sizes below about 0.7 mumol saturated phosphatidylcholine/kg body weight did not alter compliance in either group. Compliance increased to values comparable to surfactant-treated or term newborn rabbits over a narrow range of saturated phosphatidylcholine pool sizes from about 0.7 to 1.2 mumol/kg for corticosteroid-treated rabbits and from about 0.9 to about 2.3 mumol/kg for control rabbits (p less than 0.01). When these results are compared with those from surfactant-treated rabbits, almost an order of magnitude less endogenous surfactant than exogenous surfactant is needed to alter compliance in preterm ventilated rabbits.

Pregnant does were treated with betamethasone, T3, TRH, or combinations of betamethasone plus T3 or TRH using doses of each agent known to effect lung maturation. Preterm rabbits were then delivered at 27 days gestational age, half of each group was treated with Surfactant TA, and the rabbits were ventilated in a ventilator-plethysmograph system such that tidal volumes were regulated to mean values of 12 to 13 ml/kg. At 30 min of age when mean PCO2 values for the study groups were between 33 and 42 mm Hg, lung function of each rabbit was evaluated by the peak inspiratory pressure needed to achieve the desired tidal volume, by compliance, and by the ventilation efficiency index. These measures of lung function showed no benefit of corticosteroids or T3 in the absence of surfactant, whereas TRH significantly improved lung function. Although surfactant treatment improved lung function in all groups, the best effect after a single hormone treatment was with corticosteroids. The combined use of corticosteroids and TRH in surfactant-treated animals resulted in the best overall responses. The leak of protein into and out of the lungs was measured with radiolabeled albumins. The leak decreased as peak ventilatory pressures decreased in all groups and decreased with surfactant treatments of all groups. Corticosteroids decreased the protein leak into the airways more than could be accounted for by the effects of corticosteroids on ventilatory pressures alone (p less than 0.01). None of the hormone treatments significantly increased the saturated phosphatidylcholine pool sizes from the low values noted in the control animals.(ABSTRACT TRUNCATED AT 250 WORDS)