Maturation of contractile response of ductus arteriosus to oxygen and drugs.

Contractile responses of rings of ductus arteriosus from fetal and neonatal guinea pigs were studied in buffered Krebs-Henseleit solutions of various oxygen tensions. Oxygen-induced contraction of ductus arteriosus increased with gestational age, peaking at term and attenuating within 24 h after birth. Contractions of ductus in response to potassium were not different in term and preterm fetuses. Maximal contractile response of pre- and postductal aortic rings to oxygen was 8.3% of the maximal oxygen-induced contraction of ductal rings from the same fetuses. Pulmonary artery was quite insensitive to oxygen. Of 12 ductus exposed to bradykinin in the absence of oxygen seven contracted (maximal response was obtained with 15.0 ng/ml). Exposure of ductus to bradykinin in the absence of oxygen enhanced subsequent contractions of ductal smooth muscle rings to air. Atropine failed to inhibit the oxygen-induced contraction of ductus. These data suggest that acetylcholine is not essential for oxygen-induced contraction of the guinea pig ductus arteriosus.