In vitro effects of a thromboxane A2-analogue U-46619 and noradrenaline on contractions of the human thoracic duct
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A piece of a human thoracic duct removed at operation was investigated in organ baths. The duct was cut in 8 ring segments each about 1mm long and isometric tension recorded. The segments were exposed to a potassium rich (124mM) Krebs buffer solution. In only two of the segments were contractions induced (7.2 and 1.0mN, respectively). Noradrenaline and the thromboxane mimetic U-46619 induced tonic and phasic contractions. At a noradrenaline concentration of 10(-5)M the phasic contractions had a frequency of 5 min-1. The highest frequency, 9 min-1, was recorded with 3 x 10(-10)M of U-46619 present in the bath. Noradrenaline had a mean Emax of 50% of the previous K+ (124mM)-induced contraction, and the mean pEC50-value was 6.7. The Emax and pEC50-values of U-46619 were 142% and 9.5, respectively. Postjunctional alpha-adrenoceptors and thromboxane A2-receptors may play a role in the contractility of the human thoracic duct.