In Vitro Nerve-Mediated Responses in the Smooth Muscles of Lower Urinary Tract of Animals

Abstract

The neurophysiological mechanisms of the smooth muscles of the lower urinary tract have been less well studied than many other types. In the present study, the na-ture of the nerve-mediated contractions in the lower urinary tract smooth muscles from the rabbitf and pig was examined in vitro using field stimulation of muscle strips, and recording the isometric tension generated. Field stimulation produced frequencydepentdent contractions in rabbit and pig bladder strips that were partially blocked by atropine.The atropine resistant response was completely abolished by the addition of tetrodotox-in. Smaller contractile responses ot field stimulation were present in trigone and ure-thral strips. In the rabbit, the frequency-response curves showed that the contractiole re-sponses of the anterior were significantly greater than of posterior strip in both the sexes, but there was no significant difference in the response to field stim-ulation between the sexes or in the dose-response curv to carhachol between the ante-rior and posterior detrusor strips or between the sexes of the rabbit. Atropine had very little effect on the response to fieldf simulation in the rebbit urethra; phentolamine almost abolishe the contractile response to nerve stimulation. In the pig there was no significantly different response to field stimulation between the anterior and posterior detrusor or between the sexes. α , B-methylene ATP caused a partial inhibition of field stimulation in the rebbit and pig detrusor, but no effect on the urethral strips. In con-clusion, the present studies confirmed that abundant nerve distributes in the bladder, α-adrenoceptors predominated in the urethra, and non-adrentrgic non-cholinergic transmitters are involved in the mechanism function of the lower urinary.