Antenatal betamethasone attenuates intrauterine infection-aggravated hyperoxia-induced lung injury in neonatal rats

BACKGROUND: Intrauterine infection can exacerbate postnatal hyperoxic lung injury. We hypothesized that antenatal betamethasone treatment attenuates hyperoxic lung injury aggravated by intrauterine infection in neonatal rats. METHODS: Newborn Sprague-Dawley rats were divided into eight experimental groups according to (i) whether rats were exposed to normoxia (N) or hyperoxia (H, 85% oxygen) from postnatal day (P)1 to P14, (H) whether antenatal betamethasone (0.2 mg/dose) or vehicle was administered to pregnant rats at gestation days (E)19 and E20, and (Hi) whether intrauterine infection was induced or not antenatally. Intrauterine infection was induced by intracervical inoculation of Escherichia coli into pregnant rats on E19. We measured cytokine levels of tumor necrosis factor-alpha (TNF-alpha), interleukin (IL)-6, and IL-1 beta in P1 rat lungs and performed morphometric analyses and assessed inflammatory responses in lung tissue and bronchoalveolar lavage (BAL) at P14 by terminal deoxynucleotidyl transferase mediated deoxyuridine triphosphate nick end labeling (TUNEL) staining and measurement of myeloperoxidase activity, collagen, and cytokine levels. RESULTS: Cytokine levels in P1 rat lungs were increased by intrauterine infection, and these increases were attenuated by antenatal betamethasone. Hyperoxic lung injuries, indicated by morphometric changes and an inflammatory response in the lung and BAL fluid, were aggravated by intrauterine infection at P14. This aggravation was significantly attenuated by antenatal betamethasone. CONCLUSION: Antenatal betamethasone attenuated aggravated hyperoxic lung injuries induced by intrauterine infection in neonatal rats via its anti-inflammatory actions.