AIMS: The aim of this functional urodynamic experiment was to study the effect of the selective alpha1(A)-blocker tamsulosin on the urethral pressure in healthy human females and assessed first the resting urethral pressure and second the urethral contractility in response to magnetic stimulation of the sacral roots.
METHODS: 11 healthy female subjects gave their written informed consent and were included. A microtip pressure transducer catheter was inserted into the bladder and three baseline urethral pressure profiles were obtained. Another three urethral pressure profiles were recorded while magnetic single pulse stimulation of the sacral roots was performed above the motor threshold of the pelvic floor to evoke reproducible urethral contractions. Then the subjects received 0.4 mg of tamsulosin and the entire protocol was repeated 6 hours after drug administration. Cardiovascular monitoring was obtained during the baseline and follow-up measurements. Mean and maximal urethral pressure values calculated over the entire urethra, mean pressure values calculated over the proximal, middle and distal third of the urethra and the pressure amplitudes to magnetic stimulation at baseline were statistically compared to the follow-up measurements with tamsulosin.
RESULTS: The oral administration of tamsulosin did not change the systemic blood pressure, but did significantly reduce the mean and maximal urethral pressure acquired over the entire urethra. When the proximal, middle and distal third of the urethra were analysed separately, there was a significant pressure reduction in all three segments. Amplitudes of the urethral contractions evoked by sacral magnetic stimulation remained unchanged after tamsulosin.
CONCLUSIONS: These data show a significant relaxing effect of tamsulosin on the resting urethral tone in healthy females in vivo. These results may suggest tamsulosin as a new pharmacological approach to treat urinary retention due to overactive or non-relaxing urethra in women.