Effect of the alpha-adrenergic blocking agent thymoxamine on the neurogenic bladder and urethra.

The effect of the alpha-adrenergic blocking agent thymoxamine by intravenous administration was studied in 25 patients with spastic paraplegia and uninhibited neurogenic bladder. By cystometry a shift to the right of the first desire to void, the threshold of the first uninhibited contraction and a reduction of the pressures of the uninhibited contractions was found, but the bladder capacity was unchanged. The urethral pressure profile studied in 10 patients showed reduction in most and the peak value in all the patients. EMG from the external urethral sphincter in five patients showed damping of anal reflexes in all cases and in basic activity and cough reflexes when appropriate for studies. The site of action on the bladder is most likely adrenergic receptors in the bladder and the unchanged bladder capacity may be related to a too-short duration of the effect of thymoxamine. The effect on the spastic striated pelvic sphincters may be central, whereas the effect on the smooth muscle may be peripheral. Feedback from the drug relaxed proximal part of the urethra to the bladder might also be of importance.