Endothelin-1 release from lamb ductus arteriosus: relevance to postnatal closure of the vessel.

Our previous investigations have shown that endothelin-1 (ET-1) is a singularly potent constrictor of the ductus arteriosus and that a cytochrome P-450 system located in the sarcolemma is crucial for the contractile response of the vessel to oxygen. We have now studied the release of ET-1 from isolated ductus arteriosus preparations of near-term fetal lambs. Preparations produced measurable amounts of ET-1 under basal conditions (about 0.04 pg/100 mg wet weight.min) both in the presence and absence of the endothelium. Anisomycin (10(-4) M) reduced this release by 50%, while thrombin (1 U/mL) doubled the release. Treatment with a CO mixture (CO/O2 ratio, 0.27) inhibited ET-1 release from intact and endothelium-denuded preparations. We propose that oxygen triggers closure of the ductus arteriosus at birth by causing a conformational change in a specific cytochrome P-450, which, in turn, provides the signal for the synthesis of the constrictor ET-1.