Abstract
We simultaneously recorded the prostatic contractile and urethral pressure responses to electrical stimulation (ES) of the hypogastric nerves (HGNs) or phenylephrine in anesthetized rats and studied the effects of tamsulosin on these responses. At 0.01 and 0.1 mg/kg, i.v., tamsulosin inhibited the prostatic responses to ES of the HGNs in a dose-dependent manner, while at 1 μg/kg, i.v., it reduced the response to phenylephrine (0.01 mg/kg, i.v.) to about 26% of the nonantagonized level. These inhibitory effects on prostatic responses were maintained for 60 min. Tamsulosin exerted an inhibitory effect on the urethral response to ES of the HGNs at 0.01 mg/kg, i.v. but not at 0.1 mg/kg, i.v. At 1 μg/kg, i.v., tamsulosin also reduced the urethral response to phenylephrine to about 46% of the nonantagonized level; this effect was maintained for 60 min. Furthermore, tamsulosin was found to exert a stronger inhibitory effect on the prostatic response than on the urethral response induced by sympathetic nerve activation. Our findings suggest that rat urethral sympathetic nerve terminals may contain prejunctional α1 adrenoceptors that modulate the release of norepinephrine.
