Antenatal and postnatal corticosteroid and resuscitation induced lung injury in preterm sheep

Abstract

Background: Initiation of ventilation using high tidal volumes in preterm lambs causes lung injury and inflammation. Antenatal corticosteroids mature the lungs of preterm infants and postnatal corticosteroids are used to treat bronchopulmonary dysplasia.

Objective: To test if antenatal or postnatal corticosteroids would decrease resuscitation induced lung injury.

Methods: 129 d gestational age lambs (n = 5-8/gp; term = 150 d) were operatively delivered and ventilated after exposure to either 1) no medication, 2) antenatal maternal IM Betamethasone 0.5 mg/kg 24 h prior to delivery, 3) 0.5 mg/kg Dexamethasone IV at delivery or 4) Cortisol 2 mg/kg IV at delivery. Lambs then were ventilated with no PEEP and escalating tidal volumes (VT) to 15 mL/kg for 15 min and then given surfactant. The lambs were ventilated with VT 8 mL/kg and PEEP 5 cmH20 for 2 h 45 min.

Results: High VT ventilation caused a deterioration of lung physiology, lung inflammation and injury. Antenatal betamethasone improved ventilation, decreased inflammatory cytokine mRNA expression and alveolar protein leak, but did not prevent neutrophil influx. Postnatal dexamethasone decreased pro-inflammatory cytokine expression, but had no beneficial effect on ventilation, and postnatal cortisol had no effect. Ventilation increased liver serum amyloid mRNA expression, which was unaffected by corticosteroids.

Conclusions: Antenatal betamethasone decreased lung injury without decreasing lung inflammatory cells or systemic acute phase responses. Postnatal dexamethasone or cortisol, at the doses tested, did not have important effects on lung function or injury, suggesting that corticosteroids given at birth will not decrease resuscitation mediated injury.

Figure 1

Pulmonary outcomes. There were no differences between Injury, Dexamethasone (Dex), and Cortisol groups. (A) PaCO₂ decreased similarly in all groups at 15 min after the initial high V_T stretch injury, then increased with continued ventilation. PaCO₂ was lower after 120 min in the betamethasone group (Beta) relative to the injury group. (B) Ventilation efficiency index (VEI) decreased with time of ventilation, indicating progressive injury, with less decrease in the Beta group. (C) Dynamic compliance decreased following the stretch injury, with less decrease at 60 min for the Beta group. (D) Oxygenation index increased (indicating deterioration in oxygenation) with ventilation in all groups except the Beta group. t p < 0.05 vs Injury group.

Figure 2

Cytokines and Early Growth Response Protein 1 mRNA in lung tissue. (A) IL-1β mRNA and (B) Monocyte chemotactic protein 1 (MCP-1) mRNA increased with the stretch injury and ventilation in all groups relative to unventilated controls. Il-1β and MCP-1 were decreased by Betamethasone (Beta) and Dexamethasone (Dex) compared to the Injury group. (C) The increase in IL-6 mRNA with ventilation was suppressed by Beta. (D) Egr-1 mRNA increased in the Injury and Cortisol groups. Cytokine mRNA was normalized to L32 mRNA (loading control). All values reported as fold increases compared with control animals, normalized to 1. *p < 0.05 vs Controls. ^t p < 0.05 vs Injury group

Figure 3

Early Growth Response Protein 1 increased with stretch injury and ventilation. (A) Control animals show minimal staining around blood vessels. (B, D, E) The injurious ventilation increased Egr-1 protein surrounding airways, and these increases were not affected by Dex or cortisol. (C) The betamethasone group (Beta) had moderate staining around airways. (F) Semi-quantitative analysis of positive cells per high powered field demonstrated decreased staining in Beta group compared to injurious ventilation. * p < 0.05 vs control, ^t p < 0.05 vs Injury group.

Figure 4

HSP70 mRNA localization. (A) HSP70 mRNA was localized to the bronchial epithelium and parenchyma in unventilated controls. (B-E) Ventilation decreased HSP70 mRNA in airway epithelial cells and parenchyma. Injurious ventilation induced HSP70 mRNA in the smooth muscle surrounding large airways in all groups except the Beta group (C). (D) RNase protection assay for HSP70 mRNA in lung demonstrates decrease in lung mRNA with ventilation in all groups. *p < 0.05 vs controls.