Abstract
Perfusion experiments with the isolated ductus arteriosus from human fetuses showed that the cholinergic receptor function is already well developed at a gestational age of 12 weeks. Thus, acetylcholine stimulation produced prompt constriction of the ductus, and the anticholinergic drugs atropine and meperidine effectively blocked the constriction whereas morphine had no antagonistic action. The dose-effect relationship for acetylcholine constriction of the ductus did not change during growth of the fetus in the second trimester of pregnancy. Constriction was also produced by histamine but not by bradykinin. Changes in Po2 and pH of the perfusion fluid had no effect on the ductus. The results are consistent with the idea that autonomic receptor function in smooth muscles is developed early during fetal life and that the affinity for specific agonists is not changing during growth of the fetus. On the other hand, a sensitivity to changes in oxygen tension may be developing in the ductus during the last part of fetal life.
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