Developmental changes in constriction of the ductus arteriosus: Responses to oxygen and vasoactive agents in the isolated ductus arteriosus of the fetal lamb

Abstract

Development of the constrictor response of the ductus arteriosus to O2 and selected vasoactive drugs (acetylcholine and bradykinin) was studied in 20 fetal lambs weighing 68CM1800 g (90- to 150-day gestation). The isolated ductus arteriosus was perfused in vitro with Tyrode’s solution at constant flow, temperature (38°), pH (7.3-7.4), and Pcos (30,-40 mm Hg), and the mean pressure difference across the ductus was measured. Ductal resistance was calculated at different levels of Po2 (10-700 mm Hg), raised stepwise to produce dose-response curves. Three young fetuses failed to respond initially to O2 and in the other 17 the initial response occurred at progressively lower Po2 levels with advancing gestation. The maximal degree of constriction developed showed a progressive increase with advancing gestational age. At any given Po2 both acetylcholine and bradykinin produced a further increase in resistance when added to the perfusion solution, but this further increase was independent of age. The level of Po2 at which an initial response occurred was decreased after exposure to acetylcholine but not bradykinin. © 1972 International Pediatric Research Foundation, Inc.