Bladder-relaxant properties of the novel benzofuroindole analogue LDD175

The present study describes the bladder-relaxant properties of LDD175 (4-chloro-7-trifluoromethyl-10H-benzo[4,5]furo [3,2-b]indole-1-carboxylic acid), a novel benzofuroindole compound. LDD175 had no significant effect on the spontaneous and electrically evoked bladder contractions, but produced concentration-dependent relaxation in strips precontracted by 1 μmol/l acetylcholine (pEC₅₀ = 5.9 ± 0.2, E_max = 90.3 ± 2.6%; 100 μmol/l, n = 6). In high K⁺- (20 and 80 mmol/l) stimulated samples, LDD175 caused a concentration-dependent relaxant activity which was significant in 20 mmol/l K⁺ (pEC₅₀ = 5.6 ± 0.2, E_max = 63.1 ± 4.8%, n = 6), but not in 80 mmol/l K⁺ (pEC₅₀ = 5.1 ± 0.3, E_max = 12.7 ± 2.5%, n = 6). Iberiotoxin (100 nmol/l), a specific BKCa blocker, attenuated the compound's relaxative effect (vehicle = 65.7 ± 9.2% vs. iberiotoxin 28.0 ± 3.5%, respectively, n = 3), but not tetraethylammonium chloride (10 mmol/l), a nonselective K⁺ channel blocker, barium chloride (10 mmol/l), a conventional K_IR blocker, and glibenclamide (1 mmol/l), a K_ATP blocker. LDD175 was evaluated in both endothelium-intact and denuded rat aorta contracted with high K⁺. In these preparations, LDD175 did not produce significant inhibition. Administered intravenously to conscious restrained rats, LDD175 (10 mg/kg) did not alter the rat's hemodynamic activity (i.e. blood pressure and heart rate). When tested in the spontaneously hypertensive rats (SHR) for its influence on their voiding behavior, LDD175 (5 and 10 mg/kg) significantly reduced voiding frequency and lengthened void intervals of the animals. These observations: (1) reveal the BKCa channel potentiation of LDD175; (2) support previous claims concerning the bladder (vs. vascular) selectivity of benzofuroindole compounds; (3) demonstrate the efficacy of LDD175 in the animal model of bladder overactivity (SHR). Therefore, the compound may be potentially useful in the treatment of bladder overactivity.