N-[2-[4-(2-Methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-nitrophenyl) Cyclohexanecarboxamide: A Novel Pre- and Postsynaptic 5-Hydroxytryptamine_1A Receptor Antagonist Active on the Lower Urinary Tract

Abstract

N-[2-[4-(2-Methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-nitrophenyl) cyclohexanecarboxamide (Rec 15/3079) was synthesized with the aim of obtaining a novel compound with 5-hydroxytryptamine (5-HT)_1A antagonistic properties and activity in controlling bladder function at the level of the central nervous system. Rec 15/3079 showed a selective high affinity for the 5-HT_1A receptor (K_i = 0.2 nM). At the human recombinant 5-HT_1A receptor, Rec 15/3079 acted as a competitive, neutral antagonist in that it did not modify basal [³⁵S]guanosine-5′-O-(3-thio)triphosphate binding to HeLa cell membranes but shifted the activation isotherm to 5-HT to the right, in a parallel manner, with a pK_b value of 10.5. Accordingly, Rec 15/3079 (i.v.) potently antagonized 8-hydroxy-2-dipropylaminotetralin (8-OH-DPAT)-induced hypothermia in mice (ID₅₀ = 20 μg/kg) and 8-OH-DPAT-induced forepaw treading in rats (ID₅₀ = 36 μg/kg). In vitro Rec 15/3079 was poorly active in antagonizing carbachol-induced bladder (pD′₂ = 5.03) and norepinephrine-induced urethral (apparent pK_b = 6) contractions. However, in anesthetized rats, Rec 15/3079 (10–100 μg/kg i.v.) blocked isovolumic bladder contractions with no effect on their amplitude. In conscious rats and guinea pigs with bladders filled with saline, Rec 15/3079 (300–1000 μg/kg i.v.) increased bladder volume capacity (BVC) without affecting bladder contractility. In conscious rats with bladders filled with dilute acetic acid, Rec 15/3079 (300 μg/kg i.v.) reversed the decrease of BVC induced by the acid. To evaluate apparent selective effect on lower urinary tract reflexes, Rec 15/3079 was tested in experimental models for sedative, analgesic, anxiolytic, and antidepressant activity. Rec 15/3079 showed only a slight decrease in the duration of immobility in the behavioral despair test (antidepressant activity) at 1 mg/kg i.v. No anxiolytic activity was observed at 10 mg/kg i.v. No effect was observed in the hot plate test, but Rec 15/3079 increased tail-flick latencies after 3 to 10 mg/kg i.v. In conclusion, these studies demonstrate that Rec 15/3079 is endowed with favorable effects on bladder function, and it is devoid of unwanted side effects at the level of central nervous system at doses at least 10-fold higher than those active on the bladder.