KUL 7211 also reduces the spontaneous rhythmic contraction in a canine ureteral spiral preparation in a concentration-dependent manner, the pD2 value being 6.83±0.20. These data clearly demonstrate that KUL 7211 selectively stimulates both ureteral β2- and β3-adrenoceptors and potently relaxes ureteral smooth muscle.KUL 7211 ?is a new β-adrenoceptor agonist in vitro. In rat isolated organs, its selectivities, for inhibition of spontaneous uterine contraction (mediated via β2-adrenergic stimulation) and inhibition of colonic contraction (via β3-adrenergic stimulation) versus increase in atrial rate (via β1-adrenergic stimulation), are 56.3 and 242.2, respectively. KUL 7211 relaxes 80 mM KCl induced tonic contractions in both rabbit (pD2 value: 5.86±0.13, whose ureteral relaxation is mediated via β2-adrenergic stimulation) and canine (pD2 value: 6.52±0.16, via β3-adrenergic stimulation) isolated ureters in a concentration-dependent manner. These KUL 7211-induced relaxing effects are antagonized by ICI-118,551 (selective β2-adrenoceptor antagonist, pKB value: 8.91±0.24) in the rabbit ureter and by bupranolol (non-selective β-adernoceptor antagonist, pKB value: 6.85±0.12) in the canine ureter.