Effects of prazosin on isolated human urethra and in patients with lower motor neurons lesions.

In isolated human urethra, prazosin competitively inhibited contractions induced by noradrenaline, but had no effect on contractions elicited by potassium (127 mM), suggesting an action solely on alpha-adrenoceptors. Seven patients with lower motor neuron lesions and micturition disturbances were treated with 2 mg of prazosin twice daily. Five were investigated by simultaneous urethrocystometry before and during treatment. Prazosin reduced the intraurethral pressure, the intravesical pressure during bladder filling, and autonomous bladder waves. Voiding and incontinence improved in five patients. In one, voiding was facilitated, but continence deteriorated, and in one, no clinical effects were observed. In all patients, residual urine decreased. There were no side effects, except one case of nasal congestion. It is concluded that prazosin effectively reduces alpha-adrenoceptor mediated hyperactivity in the smooth muscle of the lower urinary tract, and that it may be an effective treatment of micturition disturbances in patients with lower motor neuron lesions.