Effect of antenatal dexamethasone treatment on Ca2+-dependent nitric oxidesynthase activity in rat lung

We investigated the effects of dexamethasone on nitric oxide synthase activ ity, nitrate/nitrite concentration, and cGMP concentration in the lungs of premature and full-term neonate rats. Dexamethasone or vehicle alone was ad ministered to the mother (1 mg/kg/d, s.c., 2 d), and the neonate was killed 24 h after birth. Ca2+-dependent nitric oxide synthase activity and nitrat e/nitrite and cGMP concentrations in lungs of dexamethasone-treated neonate s, both premature and full-term, were significantly higher than those in th e lungs of the control rats. Gaze-dependent nitric oxide synthase activity, nitrate/nitrite concentration, and cGMP concentration in the lungs of cont rol rats showed developmentally associated increases during late gestation and in the early postnatal period. The activation of the nitric oxide synth ase-nitric oxide-cGMP system by antenatal dexamethasone treatment may be re lated to the improvement of pulmonary function by antenatal glucocorticoid therapy to minimize respiratory distress syndrome.