Inhibition of human detrusor contraction by a urothelium derived factor

Purpose: Stimulating muscarinic receptors in pig bladder urothelium causes the release of a diffusable factor that inhibits contractions of the underlying detrusor muscle. We investigated whether the contractions of human detrusor strips elicited by the muscarinic agonist carbachol, electrical field stimulation, KCl or the neurokinin receptor agonist neurokinin A are affected by the urothelium. Materials and Methods: Paired intact and urothelium denuded muscle strips were placed in modified gassed Tyrode's solution at 37C. Cumulative concentration-response curves to carbachol or KCl were constructed. In other tissues the strips were stimulated electrically (1 to 40 Hz) with trains of square wave pulses 20 seconds in duration at 5-minute intervals. Results: Cholinergic contractions evoked by electrical field stimulation at 10 and 30 Hz or by carbachol were significantly inhibited in the presence of an intact urothelium. Contractions elicited by KCl and by 10 μM neurokinin A were not modified by the urothelium. The urothelium mediated inhibition of contractions induced by carbachol was not affected by 300 μM L-N ^G-nitroarginine, 1 μM ODQ (1H-[1,2,4]oxadiazolo[4,3-α ]quinoxalin-1-one), 1 μM propranolol or 5 μM indomethacin. Conclusions: Muscarinic agonists stimulate the release of an inhibitory factor from the human urothelium. The factor is distinct from nitric oxide and it persists in the presence β-adrenoceptor blockade or cyclooxygenase inhibition.