Antenatal betamethasone therapy augments nitric oxide-mediated
relaxation of preterm ovine pulmonary veins.
Zhou, Haiyan, Yuansheng Gao, and J. Usha Raj.
Department of Pediatrics, Harbor-UCLA Medical Center, University of
California, Los Angeles, School of Medicine, Torrance, CA 90509
APStracts 2:0434A, 1995.
Antenatal glucocorticoid therapy improves pulmonary function in
preterm newborns. We have determined the effect of antenatal
glucocorticoid therapy on nitric oxide-mediated relaxation in
pulmonary vessels of preterm lambs. Ovine fetuses (126 d gestation;
term=150 d) were injected with betamethasone, 0.5 mg/kg body weight,
or saline. After 48 h, lambs were delivered, ventilated for 3 h, and
sacrificed. Isolated fourth generation pulmonary arteries (diameter:
2-3 mm) and veins (diameter: 1.5-2 mm) were suspended in organ
chambers filled with modified Krebs-Ringer solution (95% O2, 5% CO2)
at 37 degrees C and their isometric tension recorded. During
contractions to endothelin-1 or U46619 (in the presence of
indomethacin), acetylcholine and bradykinin induced endothelium
-dependent, nitro-L-arginine-inhibitable relaxation in arteries and
veins. The relaxation was greater in veins of betamethasone-treated
lambs than in those of control lamb. Veins without endothelium
treated with betamethasone were more sensitive to sodium
nitroprusside than those of control. For arteries, there was no
significant difference in relaxation between different groups.
Relaxation induced by 8-bromo-cyclic GMP was similar in arteries and
veins of different groups. Radioimmunoassay showed nitric oxide
caused a greater increase in cyclic GMP in betamethasone-treated
veins than in control. These data suggest that antenatal
betamethasone therapy augments nitric oxide-mediated relaxation of
pulmonary veins of preterm lambs, probably by increasing soluble
guanylate cyclase activity of vascular smooth muscle.
Received 31 March 1995; accepted in final form 22 September 1995.
APS Manuscript Number A359-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95