INVESTIGATIVE UROLOGY

An in vitro study on human ureteric smooth muscle with the alpha1-adrenoceptor subtype blocker, tamsulosin
Rajpathy J, Aswathaman K, Sinha M, Subramani S, Gopalakrishnan G, Kekre NS
British Oxygen Company Limited, Chennai, India
BJU Int. 2008; 102: 1743-5.

• Objective: To study the effects of tamsulosin on ureteric contractions and its effects on the basal tone of human ureteric specimens, as clinical trials with tamsulosin have shown promising results in the spontaneous expulsion of lower ureteric calculus, but the mechanism of action of tamsulosin in the expulsion of ureteric calculus has not been elucidated in in-vitro studies on human ureters.
• Materials and Methods: Human mid-ureteric specimens were obtained from live kidney donors. The specimen was transported in Krebs’ solution and the isometric contraction of human ureteric smooth muscle was recorded in the presence of tamsulosin. Ureteric rings from 19 kidney donors were studied.
• Results: At 100 microm tamsulosin the frequency of ureteric contraction was blocked completely, or the contraction frequency was reduced in 89% of specimens. There was no change in the frequency or in the amplitude of contraction in the remaining specimens. The basal tone of the ureter was reduced in 16% of the specimens.
• Conclusion: Our results suggest that peristaltic activity in human ureteric smooth muscle is inhibited by tamsulosin. The effect of tamsulosin on basal tone is marginal.
  
  
• Editorial Comment
  Previous studies hypothesized that tamsulosin relaxes the ureteric smooth muscle, thereby facilitating the spontaneous passage of stone. Clinical studies demonstrated that tamsulosin decrease the colic pain and the number of colic episodes. Nevertheless, the exact mechanism of action is still controversial. The authors found that tamsulosin decreased or completely blocked the peristaltic contractions in 17 of 19 ureteric specimens studied in vitro. However, tamsulosin did not produce a decrease in baseline tension in 16 of 19 specimens. The results of this work support that the mechanism of action of tamsulosin is the inhibition of peristaltic contractions, and do not support the hypothesis that it causes a relaxation of ureteric smooth muscle.
  In conclusion, the present study elegantly demonstrates that peristalsis in human ureter is inhibited by tamsulosin.

Dr. Francisco J. B. Sampaio
Full-Professor and Chair, Urogenital Research Unit
State University of Rio de Janeiro
Rio de Janeiro, RJ, Brazil
E-mail: sampaio@urogenitalresearch.org