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

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.

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.

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.

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