Comparison between tamsulosin and alfuzosin on the expulsion phase of ejaculation in rats.

OBJECTIVE: To investigate the effects of acute intravenous (i.v.) delivery of tamsulosin and alfuzosin on the contractions of bulbospongiosus muscles (BS) induced by central delivery of a serotonin agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), in anaesthetized rats, as an experimental model of the expulsion phase of ejaculation.

MATERIALS AND METHODS: Under urethane anaesthesia, adult male rats were implanted with a cannula into the lateral cerebral ventricle for intracerebroventricular (i.c.v.) injection, and with recording electrodes in the BS for electromyogram (EMG) monitoring. Tamsulosin (1 microg/kg) and alfusozin (10 microg/kg) were injected i.v. and 15 min later 8-OH-DPAT (20 microg) was delivered i.c.v. BS-EMG recording was continued for 30 min after i.c.v. 8-OH-DPAT. The area under the curve (AUC) of the BS cluster of contractions was determined as reflecting the energy of BS contractions.

RESULTS: After i.c.v. delivery of 8-OH-DPAT, there were rhythmic BS contractions in the form of clusters of bursts in vehicle-, tamsulosin- and alfuzosin-treated rats. The number of BS clusters was not altered by the alpha1-blockers as compared with vehicle, but the AUC was significantly less in tamsulosin-treated rats than in vehicle- or alfuzosin-treated (both P < 0.05) rats.

CONCLUSION: Systemic injection of tamsulosin impaired BS contractile capacity whereas alfuzosin did not. This might explain anejaculation in men treated with tamsulosin.