Effects of antenatal glucocorticoids on circulatory adaptation at birth in the ovine fetus.
OBJECTIVE
Adaptation to extra-uterine life requires dramatic increase in pulmonary blood flow. Mechanisms that induce pulmonary vasodilatation at birth are incompletely understood but include alveolar ventilation, increase in PaO2, and production of vasoactive mediators. We hypothesized that antenatal glucocorticoids (GC) increase pulmonary vasodilatation to birth-related stimuli.


METHODS
To test this hypothesis, we studied the pulmonary hemodynamic response at birth to mechanical ventilation with low (<10%) and then with high (100%) FiO2 in chronically prepared late-gestation fetal lambs treated or not by antenatal maternal steroids.


RESULTS
Basal mean aortic and pulmonary artery pressure (PAP), left pulmonary blood flow, pulmonary vascular resistance (PVR), and blood gas were similar between control and dexamethasone-treated animals (GC group). During mechanical ventilation with low FiO2, mean PVR decreased by 40% in the control group (from 0.44 +/- 0.01 to 0.25 +/- 0.01 mm Hg/ml/min) and by 60% in the GC group (from 0.44 +/- 0.02 to 0.19 +/- 0.02 mm Hg/ml/min) (p < 0.01). When subsequently ventilated with 100% O2, there was no difference in PVR decrease between groups (0.15 +/- 0.02 mm Hg/ml/min in the GC group vs. 0.14 +/- 0.01 mm Hg/ml/min in the control group).


CONCLUSIONS
Antenatal GC enhance pulmonary vasodilatation induced by alveolar ventilation at birth but do not alter the pulmonary vascular response to O2. We speculate that antenatal steroids exposure improve adaptation at birth through acceleration of both parenchymal and vascular lung maturation.
Houfflin-Debarge
V
V
Department of Obstetrics, Centre Hospitalier Régional Universitaire de Lille, Lille, France. v-houfflin-debarge@chru-lille.fr
Deruelle
P
P
Jaillard
S
S
Magnenant
E
E
Riou
Y
Y
Devisme
L
L
Puech
F
F
Storme
L
L
D000222:Adaptation, Physiological / Q000187:drug effects*; D000818:Animals; D000831:Animals, Newborn; D003907:Dexamethasone / Q000494:pharmacology*; D005260:Female; D005333:Fetus / Q000187:drug effects; D005938:Glucocorticoids / Q000494:pharmacology*; D006439:Hemodynamics; D010100:Oxygen / Q000032:analysis; D011247:Pregnancy; D011270:Pregnancy, Animal; D011652:Pulmonary Circulation / Q000187:drug effects*; D012756:Sheep; D014664:Vasodilation / Q000187:drug effects
D005938:Glucocorticoids; D003907:Dexamethasone; D010100:Oxygen