The effects of the constituents of Baralgin ® (metamizole, fenpiverinium, and pitofenone) on mechanical activity were studied in isolated human preparations of the upper urinary tract. Metamizole in concentrations up to 10––3 mol/l did influence neither spontaneous phasic activity nor activation by high external potassium, norepinephrine, or acetylcholine. Fenpiverinium blocked the increase in frequency of phasic-rhythmic contractions and the tonic tension development induced by acetylcholine. Fenpiverinium did influence neither spontaneous phasic activity nor activation by high potassium or norepinephrine. Pitofenone (10––3 mol/l) antagonized completely spontaneous phasic-rhythmic as well as norepinephrine- or acetylcholine-induced phasic activity. The tonic activation induced by norepinephrine and acetylcholine was nearly completely inhibited. Pitofenone (10––6 to 10––3 mol/l) antagonized the high potassium-induced activation in a concentration-dependent way. The EC50 of pitofenone amounted to 2 × 10––4 mol/l. Uptake measurements of 14C-pitofenone (2 × 10––4 mol/l) in isolated ureteral segments showed the drug to be accumulated in the ureteral tissue; a tissue/medium ratio of about 3 was found at an exposure time of 60 min. The accumulation of the drug was reversible after washing in drug-free solution, indicated by the loss of radioactivity increasing with longer washing times. The results show that pitofenone has a direct relaxant effect on smooth muscle of the upper urinary tract, whereas fenpiverinium has exclusively anticholinergic properties. Metamizole had no direct effect on smooth muscle activity, and its clinical effects may be rather due to its analgesic action.

Keywords:
Human ureter, Smooth muscle, Contraction, Relaxation, Baralgin®, In vitro
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© 1984 S. Karger AG, Basel
1984
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