Pulmonary antioxidant enzyme activity during early development: Effect of ventilation.

OBJECTIVE: To examine the effect of tidal liquid ventilation (TLV) and conventional gas ventilation (GV) on the pulmonary antioxidant enzyme (AOE) activity in two groups of preterm lambs at 110 and 120 days of gestation and to compare these results to age-matched fetal controls. DESIGN: Experimental, prospective, randomized, controlled study. SETTING: School of medicine, department of physiology. SUBJECTS: Thirty-two premature lambs at 110 days (n = 16) and 120 days (n = 16) gestation. INTERVENTIONS: Six lambs at 110 and 120 days were ventilated with TLV for 4 hrs. Three lambs at 110 days were ventilated with GV for 3 hrs, and six lambs at 120 days were ventilated with GV for 4 hrs. Four lambs, each at 110 and 120 days, were used as age-matched fetal controls. Measurements: Sequential measurements of arterial blood chemistries were performed in all groups. Biochemical assays included catalase activity, superoxide dismutase activity, and glutathione peroxidase activity. Histologic examinations of lung sections from TLV and GV lungs were performed. Main Result: Despite vast differences in physiologic outcome, there were fewer differences in AOE activity as a function of ventilation (fetal control, GV, and TLV lambs) and/or gestational age. There were no significant differences in superoxide dismutase and glutathione peroxidase activity as a function of age or ventilation. Catalase activity was significantly higher (p <.05) in fetal 120-day control lambs (24.8 +/- 1.9 units/mg protein) relative to the 110-day control lambs (14.3 +/- 1.7 units/mg protein). Catalase activity significantly (p <.05) decreased in both GV and TLV 120 day lambs compared with fetal controls; yet, in the 110-day gestational lambs, there were no significant differences in enzyme level as a function of ventilation. Thus, an age-specific response to ventilation was evident for catalase activity. CONCLUSION: The present data demonstrate several developmental differences in AOE activity. The lack of ventilation effect in AOE activity, in view of the big difference in physiologic and inflammatory outcomes, suggests that mechanisms associated with free radicals do not underlie the response to different modes of ventilation.