Developmental response to indomethacin: A comparison of isometric tension with PGE2 formation in the lamb ductus arteriosus

We studied the effects of oxygen and indomethacin on the isometric contractile response and the production of PGE₂ in isolated rings of lamb ductus arteriosus from animals of different gestational ages (100 to 144 days; term is 150 days). Rings of ductus arteriosus from animals less than 110 days released significantly less PGE₂ than did rings from animals greater than 120 days. The indomethacin-induced increase in muscle tension in relation to the decrease in endogenous PGE₂ production in preparations from animals less than 110 days gestation was greater than in animals older than 120 days. These findings do $\text{not}$ support the hypothesis that immature animals have a larger indomethacin-induced contraction due to an increased production of PGE₂ earlier in gestation. They are, however, consistent with a decreased sensitivity to PGE₂ in the more mature animals; they also support the hypothesis that the decreased effectiveness of indomethacin on the ductus arteriosus from later gestation animals reflects primarily a decrease in the sensitivity of the vessel to PGE₂ during development.