Betamethasone-mediated vascular dysfunction and changes in hematological profile in the ovine fetus

Glucocorticoid administration to fetal sheep induces a sustained systemic b lood pressure rise and an associated increase in femoral vascular resistanc e. We utilized a small vessel myograph to compare isometric vascular respon ses of small femoral arterial branches from fetal sheep infused intravenous ly with either betamethasone or vehicle in vivo from 128 days gestation. Ch anges in hematological parameters were also determined. Betamethasone was i nfused for 48 h to produce fetal plasma betamethasone concentrations simila r to those observed in human fetuses after maternal treatment with betameth asone to accelerate fetal lung maturation. When compared with vessels remov ed from vehicle-infused fetuses, vessels obtained from betamethasone-treate d fetuses exhibited 1) enhanced sensitivity to depolarizing potassium solut ions; 2) no differences in response to the thromboxane mimetic U-46619 or n orepinephrine; and 3) differential responses to vasodilators, enhanced sens itivity to ACh, but decreased response to bradykinin and forskolin. In addi tion, erythrocyte and leukocyte counts were increased in betamethasone-infu sed fetuses. These observations indicate that multiple mechanisms operate t o increase fetal vascular resistance during antenatal betamethasone exposur e.