Ys. Gao et al., A SINGLE-DOSE OF ANTENATAL BETAMETHASONE ENHANCES ISOPRENALINE AND PROSTAGLANDIN E-2-INDUCED RELAXATION OF PRETERM OVINE PULMONARY-ARTERIES, Biology of the neonate, 73(3), 1998, pp. 182-189
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.