Terbutaline alleviates the lung injury in the neonatal rats exposed to endotoxin: Potential roles of epithelial sodium channels

Abstract

Intrauterine inflammation generates inflammatory mediators that damage the developing bronchoalveolar epithelium, resulting in neonatal lung injury. Lung fluid transport disorders are the main reasons for the development of pulmonary edema, an important pathology of lung injury. Previous studies suggested that epithelial sodium channels (ENaCs) play an important role in lung fluid transport. Here, we investigated whether changes in the expression of ENaCs were observed when neonatal rat lung injury was induced by maternal exposure to endotoxin. We also examined the therapeutic effect of terbutaline nebulizer inhalation on this injury. The results showed that maternal exposure to endotoxin increased the levels of TNF-α and IL-1β in bronchoalveolar lavage fluid, suppressed α-, β-, γ-ENaC in the neonatal rat lung, and resulted in the formation of pulmonary edema on postnatal days 1 and 7. Terbutaline up-regulated the expression of β- and γ-ENaC in the distal lung after 7 days of treatment. The potential signal molecules cAMP, PKA, and CREB expressions were increased after terbutaline treatment. In summary, maternal exposure to endotoxin decreased the expression of ENaCs in neonatal rats which, in turn, may exacerbate pulmonary edema. Inhalation of the β2-adrenergic receptor agonist terbutaline improved lung liquid clearance. By increasing the expression of sodium ion channels, the effective removal of alveolar fluid provides a new way for the prevention and treatment of neonatal lung injury.

Keywords: endotoxin; epithelial sodium channels; lung injury; neonatal rat; terbutaline.

Figure 1

Terbutaline reduced the intrauterine inflammation in the lung tissues from neonatal rats treated with endotoxin. A and B, Effects of terbutaline on LPS‐induced lung histological alterations and pathological score after LPS challenge on P1 and P7 (H&E stain, magnification ×200). C, Effects of terbutaline on wet/dry ratios in neonatal lungs on P1 and P7 after LPS challenge. Lung wet/dry weight ratios in the terbutaline group were significantly lower than those in the LPS group. Data are presented as means ± SD. *P < 0.05 compared with the control group, #P < 0.05 compared with the LPS group, n = 8 in each group

Figure 2

Terbutaline decreased the BALF levels of TNF‐α and IL‐1β after LPS treatment. A, Effects of terbutaline on the levels of TNF‐α on P1 and P7 in neonatal rat BALF after LPS treatment. B, Effects of terbutaline on the levels of IL‐1β on P1 and P7 in neonatal rat BALF after LPS treatment. C and D, The expression of TNF‐α and IL‐1β mRNA decreased after terbutaline treatment. Data are presented as means ± SD. *P < 0.05 compared with the control group, #P < 0.05 compared with the LPS group, n = 8 in each group

Figure 3

Terbutaline reversed the effects of LPS on ENaC expression. Effects of terbutaline on mRNA transcription levels of the alveolar epithelial sodium channel (ENaC) in neonatal rat lungs on P1 and P7 after LPS treatment (A, α‐ENaC; D, β‐ENaC; G, γ‐ENaC). Effects of terbutaline on protein expression levels of the cell membrane alveolar epithelial sodium channel (ENaC) in neonatal rat lungs on P1 and P7 after LPS treatment (B and C, α‐ ENaC; E and F, β‐ENaC; H and I, γ‐ENaC). Data are presented as means ± SD. *P < 0.05 compared with the control group, #P < 0.05 compared with the LPS group, n = 8 in each group

Figure 4

Terbutaline upregulated α‐ENaC in the alveolar epithelium. A, immunohistochemistry, brown yellow particles as positive expression; B, immunofluorescence stain, bright green particles as positive expression, magnification ×200). The arrow pointed to the positive‐stained cells

Figure 5

Terbutaline increased cAMP, PKA, and CREB in the neonatal lungs treated with endotoxin. A, cAMP; B, PKA; C, CREB. Data are presented as means ± SD. *P < 0.05 compared with the control group, #P < 0.05 compared with the LPS group, n = 8 in each group