Effects of intrathecal injection of tamsulosin and naftopidil, alpha-1A and -1D adrenergic receptor antagonists, on bladder activity in rats.

The effects of intrathecal injection of tamsulosin (an alpha-1A adrenergic receptor antagonist) and naftopidil (an alpha-1D adrenergic receptor antagonist) on isovolumetric bladder contraction were investigated in rats under urethane anesthesia. Intrathecal injection of tamsulosin (10-30 microg) or naftopidil (0.1-30 microg) transiently abolished isovolumetric rhythmic bladder contraction. Following the recovery of bladder contraction, the interval between contractions was the same as the control value before the injection. The amplitude of bladder contraction was decreased by intrathecal injection of naftopidil (3-30 microg), but not by tamsulosin. Therefore, in addition to the antagonistic action of these agents on the alpha-1 adrenergic receptors of prostatic smooth muscle, both agents (especially naftopidil) may also act on the lumbosacral cord, and thus may improve collecting disorders in patients with benign prostatic hyperplasia.