THE ACTION OF 5‐HYDROXYTRYPTAMINE AND SOME OF ITS ANTAGONISTS ON THE UMBILICAL VESSELS OF THE HUMAN PLACENTA

Abstract

The vasoconstrictor action of 5‐hydroxytryptamine (5‐HT) in the human placental preparation is about 10 times stronger than that of adrenaline and is antagonized by anti‐adrenaline compounds like phentolamine. Both 5‐HT and adrenaline are antagonized by yohimbine and chlorpromazine. Specific and strong anti‐5‐HT action is demonstrated for lysergic acid diethylamide (LSD) and tryptamine. Both LSD and tryptamine in larger doses have a vasoconstrictor action. Mescaline has no certain modifying effect on the action of 5‐HT, but itself causes vasoconstriction in large doses. The antihistamine drug phenbenzamine in histamine blocking doses abolishes the action of 5‐HT in half the preparations tested. The ganglionic blocking agent trimetaphan in large doses antagonizes the action of 5‐HT added subsequently, and also, to a lesser degree, the effect of adrenaline. Hexamethonium and tetraethylammonium bromides are ineffective in this preparation. No certain modifying action of reserpine on subsequently added 5‐HT could be demonstrated, and the same was true for heparin even in very high concentrations.