[Action of acetylcholine and carbamylcholine on spontaneous rates of hearts isolated from human embryos].

Fifty-eight early human foetal hearts, which had been obtained from cases of legal termination of pregnancy, were studied for their sensitivity to acetylcholine. Acetylcholine action was found to cause moderate decline in spontaneous human embryonic heart rate around the fifth and sixth weeks of development. The sensitivity to acetylcholine of the embryonic heart, aged between five and eight weeks, was found to go up along with growing age. The action of carbamylcholine, another cholinergic stimulant, was studied in some of the cases. Bradycardic action of carbamylcholine upon hearts aged between nine and ten weeks was found to be much stronger than that on hearts aged between five and six weeks. --The findings recorded from these studies have produced evidence to the effect that parasympathetic innervation in human embryonic hearts was preceded by the appearance of cholinergic receptors. They have also shown that in a very early phase of ontogenesis considerable change is undergone also by the cholinergic receptors of the heart.