Objective: To evaluate differing methods of stimulation on strips of human bladder neck smooth muscle and compare muscle taken from the anterior and posterior aspects.
Materials and methods: Samples of adult human male bladder neck muscle were obtained from patients undergoing open radical prostatectomy. Muscle was taken from either the anterior or posterior (nine and six patients, respectively) aspects of the bladder neck. Muscle strips dissected from these samples were suspended in the Brading-Sibley organ bath. The strips were superfused with 100 mm KCl-enriched Krebs' solution for 4 min to determine viability. This allowed experimentation on 17 strips from the anterior aspect of the bladder neck and 13 from the posterior bladder neck. These remaining strips were then superfused either with various concentrations (x10(-7) to x10(-3)m) of carbachol or noradrenaline in Krebs' solution, for 15 s. A further set of strips (eight from anterior, six from posterior) was suspended and responses to electrical field stimulation (EFS) with varying parameters were measured. Each EFS experiment was repeated after a 15 min exposure to 10(-3)m atropine, and again after a 15 min exposure 10(-7)m tetrodotoxin (TTX). Tension responses produced in these series of experiments were measured using strain gauges and analysed using data acquisition software. Student's t-test was used for the statistical analysis.
Results: All muscle strips included in the study responded to EFS. The magnitude of this contraction is frequency dependent. The contractions were abolished by superfusion of the muscle strips with atropine. There was no further suppression of the contractile response on addition of TTX. Posterior bladder neck samples had a greater mean contractile response per unit mass than anterior strips at all frequencies of >1 Hz, and significantly more at 20 and 30 Hz. There was a concentration-dependent response in bladder neck contraction to carbachol but only in the strips from the anterior bladder neck at concentrations of <10(-3)m. Posterior bladder neck strips did not significantly contract upon application of carbachol. Similarly, there was a concentration-dependent response to noradrenaline. Responses to noradrenaline were not uniform around the bladder neck, but not significantly different. Carbachol was the more 'potent' stimulator in anterior smooth muscle strips, but again the differences between agonists were not statistically significant.
Conclusion: These experiments show physiological variability around the circumference of the human male bladder neck. The posterior bladder neck shows significantly stronger contraction to alpha-adrenergic agonists compared with cholinergic agonists; the anterior bladder neck does not have a similarly significant differential response. The uniform response to noradrenaline may underlie the bladder neck's role in the prevention of retrograde ejaculation. The differential responses to carbachol may reflect differences in the embryological derivation of the anterior and posterior bladder neck fibres or in their innervation. Some of these differences may have clinical importance through the action of therapeutic agents.