Endothelin-1-endothelin receptor type A mediates closure of rat ductus arteriosus at birth

1. The ductus arteriosus (DA) undergoes rapid closure after birth as pulmonary circulation is established. The involvement of endothelin-1 (ET1) in this closure mechanism is controversial. 2. The effect of ATZ1993 (ATZ), a non-peptide antagonist for the ET(A) and ET(B) receptors, on postnatal closure and O2-induced contraction of the rat DA was investigated both in vivo and in vitro. Rat pups were delivered by Caesarean section and were given ATZ intraperitoneally. The minimum external DA diameter and the extent of DA constriction in vivo were evaluated at 2.5 h after birth. ATZ caused a dose-dependent inhibition of DA closure in vivo. When rat pups were given ATZ at 2.5 h after birth, re-opening of the DA was observed. 3. In vitro, ATZ also caused a marked inhibition of O2-induced and ET1-induced DA contractions as did BQ123, an ET(A)-specific antagonist. In contrast, sarafotoxin S6c, an ET(B)-specific agonist, did not cause DA contraction and BQ788, an ET(B)-specific antagonist, did not affect O2-induced DA contraction. 4. In conclusion, ET1 and its cognate receptor ET(A) may play a physiological role in the postnatal closure of the rat DA in vivo.