Corticosteroids, thyrotropin-releasing hormone, and antioxidant enzymes in preterm lamb lungs

Forty-three twin lamb fetuses of 121 +/- 1 d gestation were catheterized and received i.v. saline (n = 8), 0.75 mg/kg/h cortisol for 60 h (n = 15), 5 micrograms/kg thyrotropin-releasing hormone (TRH) every 12 h for five doses (n = 9), or cortisol and TRH (n = 11) before delivery at 128 +/- 1 d. After delivery, the lambs were randomized for natural sheep surfactant treatment or sham treatment, ventilated for 75 min, and killed. Superoxide dismutase, catalase, and glutathione peroxidase activities were measured in fetal lung tissue. Superoxide dismutase and catalase activities were increased in both the corticosteroid (p less than 0.001) and the corticosteroid with TRH (p less than 0.01) groups. Glutathione peroxidase activity was higher after prenatal corticosteroid treatment, but statistical significance was not reached (p = 0.06). Although prenatal exposure to corticosteroids increased superoxide dismutase, catalase, and glutathione peroxidase activities, TRH alone or TRH added to corticosteroids provided no additional benefit. Lambs treated with surfactant had higher lung catalase activities than lambs that did not receive surfactant, probably secondary to the presence of catalase activity in the surfactant preparation. Increased pulmonary antioxidant enzyme activity may be an additional feature of the overall beneficial effect of corticosteroids on fetal lung development.