Pharmacological analysis of vasoconstrictor responses of isolated and perfused human umbilical arteries.

Using the cannula inserting method, we studied vascular responses of isolated human umbilical arteries to several vasoactive substances. ACh did not produce a vasodilation in non-constricted preparations but induced only a vasoconstriction. Histamine and 5HT produced strong vasoconstrictions in a dose-dependent manner. Epinephrine and norepinephrine in large doses induced only a slight vasoconstriction. The ACh-induced vasoconstriction was markedly suppressed by atropine and slightly, but significantly, suppressed by methylsergide. The vascular responses to ACh were not influenced by removal of the endothelium by an intraluminal bolus injection of saponin. These results suggest that the endothelium has no muscarinic receptors in the umbilical arteries, although cholinergic vasoconstrictor mechanisms may be partially involved in the regulation of umbilical circulation, and that human umbilical arteries exhibit different pharmacological responses from those of vessels of other organs.