COMPARISON OF THE EFFECTS OF OXYGEN, 5-HYDROXYTRYPTAMINE, BRADYKININ AND ADRENALINE IN ISOLATED HUMAN UMBILICAL ARTERY SMOOTH MUSCLE

¹ Autonomic Physiology Unit, Institute of Physiology, University of Glasgow, Glasgow G12 8QQ
² Analytical Pharmacology Group, Department of Biochemical Sciences, Wellcome Research Laboratories, Langley Court, Beckenham, Kent BR3 3BS
³ Queen Mother's Hospital Glasgow

The actions of 5-HT, bradykinin and adrenaline on the isolated human umbilical artery (HUA) were examined in paired isometric and isotonic preparations and in paired isometric and perfused preparations at both low (20 mmHg) and high (120 mmHg) oxygen tensions. The response to each agonist was potentiated by the higher oxygen tension in all test systems. The relative potency of the three agonists studied was similar using each of the experimental techniques. The contractions to stepped increments in oxygen tension were compared in isometric and isotonic preparations. The thresholds were found to be 20 and 28 mmHg respectively. The maximum contraction occurred at 234 and 199 mmHg respectively. In the perfused (constant flow rate) preparations, oxygen did not evoke any increase in perfusion pressure unless the vessel was held under longitudinal tension, in which case the pressor responses were similarly concentration dependent as for isometric and isotonic preparations. Responses to 5-HT, bradykinin and adrenaline in the perfused preparation were similar with or without application of longitudinal tension. It is concluded that oxygen may contract only the longitudinal muscle whereas 5-HT, bradykinin and adrenaline act on both longitudinal and circular muscle. The possible roles which these agonists may play in the regulation of umbilical blood flow are discussed.

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