A SINGLE-DOSE OF ANTENATAL BETAMETHASONE ENHANCES ISOPRENALINE AND PROSTAGLANDIN E-2-INDUCED RELAXATION OF PRETERM OVINE PULMONARY-ARTERIES

beta-Adrenergic agonists and prostaglandin E-2 (PGE(2)) play an import ant role in perinatal pulmonary circulation. We have determined the ef fect of antenatal glucocorticoid treatment on isoprenaline- and PGE(2) -mediated relaxation of pulmonary arteries of newborn preterm lambs. O vine fetuses (121 days of gestation; term = 150 days) received a singl e intramuscular dose of betamethasone (0.5 mg/kg) or saline. Fifteen h ours after the injection, the lambs were delivered, ventilated for 3 h , and sacrificed. The fourth-generation pulmonary arteries were dissec ted and cut into rings for study. In endothelin-1-preconstricted vesse ls, isoprenaline, PGE(2), and forskolin (an activator of adenylyl cycl ase) induced greater relaxations of pulmonary arteries of betamethason e-treated lambs than those of controls. 8-Bromo-cyclic adenosine monop hosphate, a cell membrane permeable analogue of cyclic adenosine monop hosphate, caused similar relaxation of all vessels. When stimulated wi th isoprenaline and PGE(2), the adenylyl cyclase activity of crude mem brane preparations of pulmonary arteries treated with betamethasone wa s greater than that of controls. These results show that single-dose a ntenatal betamethasone treatment enhances relaxation of pulmonary arte ries of preterm lambs induced by isoprenaline and PGE(2) and that an e nhanced adenylyl cyclase activity contributes to the effect of betamet hasone on pulmonary arteries of preterm lambs.