The potency of KUL-7211, a selective ureteral relaxant, in isolated canine ureter: comparison with various spasmolytics

We compared the potency of a selective ureteral relaxant KUL-7211 (β₂/β₃-adrenoceptor agonist; (-)-2-[4-(2-{[(1S,2R)-2-hydroxy-2-(4-hydroxyphenyl)-1-methylethyl]amino}ethyl)phenyloxy]acetic acid) with those of various spasmolytics on contractions in isolated canine ureteral preparations. Drug effects were evaluated on the tonic contraction induced by KCl (80 mM) and on spontaneous, 1×10⁻⁵ M phenylephrine-, and 1×10⁻⁶ M PGF_2α-induced rhythmic contractions in isolated canine ureteral preparations using a functional experimental technique. The potencies (pD₂ value) of the following drugs were compared: KUL-7211, tamsulosin (an α_1A/1D-adrenoceptor antagonist), prazosin (an α₁-adrenoceptor antagonist), verapamil (a Ca²⁺-channel blocker), butylscopolamine (a nonselective muscarinic antagonist), and papaverine (a phosphodiesterase inhibitor). The rank order of relaxing potencies against KCl-induced tonic contraction was KUL-7211 (6.60)>tamsulosin(5.90)>verapamil(5.70)>papaverine(4.88)>prazosin (4.54). The rank order of potencies for reductions in spontaneous rhythmic contractions was KUL-7211 (6.80)>verapamil(6.12)>papaverine(5.05). Conversely, high concentrations of the two α-adrenoceptor antagonists (tamsulosin and prazosin) and of butylscopolamine enhanced the spontaneous contractions, although at low concentrations (up to 1×10⁻⁶ M) they had no significant effects. For suppression of spasmogen-induced rhythmic contractions, the rank order of potencies was, against phenylephrine-induced contractions: KUL-7211 (6.95)>tamsulosin(6.26)>prazosin(5.68)>verapamil(5.64)>papaverine (5.03), and against PGF_2α-induced contractions: KUL-7211 (7.05)>verapamil(6.70)>papaverine (5.27). Our results suggest that in dogs, the β₂/β₃-adrenoceptor agonist KUL-7211 is the most efficacious ureteral relaxant among the spasmolytics tested against various contractions. Possibly, KUL-7211 might be useful for promoting stone passage and relieving ureteral colic in urolithiasis patients.