AbstractDetrusor and trigone from man and detrusor, trigone, bladder neck, and urethral smooth muscle from pig were investigated in a series of experiments in vitro. A noncholinergic, nonadrenergic inhibitory nerve response was demonstrated. In the outlet smooth muscle, the onset of the relaxation was fast and sustained during stimulation. The amplitude of the relaxation was proportional to the basal tension and maximal with stimulation frequencies of 5‐10 Hz. In pig detusor, the relaxation was preceded by a contractile phase. Spontaneous or induced contractility and high tension favoured the relaxation in a nonlinear way. In human detrusor the relaxation was difficult to generate and the results were equivocal. No tested transmitter candidate mimicked exactly the relaxation evoked by electric nerve stimulation. Acetylcholine, noradrenaline, enkephalins, substance P, histamine, and prostaglandins were excluded. Vasoactive intestinal polypeptide induced relaxation in both detrusor and outlet muscles. Serotonin and ATP induced contraction in the detrusor and relaxation in pig outlet muscle. However, the relaxationevoked pharmacologcally developed slowly and the amplitudes were submaximal. The relaxation evoked by ATP was probably caused by adenosine after degradation of ATP. No other known and tested transmitter candidate evokes relaxation in lower urinary tract smooth muscle.Bladder neck smooth muscle biopsies from men with bladder neck dyssynergia, median‐sized benign prostatic hypertrophy, and normal infravesical outlet were analysed for vasoactive intestinal polypeptide by radioimmunoassay and by immunohistochemistry. No diferences were found between the groups. Pressure‐flow‐EMG studies were performed in men and urethrocystometry was performed in women before, during, and after vasoactive intestinal polypeptide 3 μg/kg × h intravenously. No systematic changes developed in any of the urodynamic p
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