The Role of Ureteral Relaxation in the Promotion of Stone Passage

In order to promote stone passage in renal colic, we must first understand normal ureteral activity and how this is affected by the presence of a stone. Measuring normal ureteral activity in humans is difficult without the use of invasive methods or techniques which in themselves may affect peristalsis. Monitoring the activity during confirmed renal colic is even more difficult and virtually impossible. Both animal and human studies have therefore been used in an attempt to understand the physiology of the ureter and how this is affected by the presence of a stone. Using this knowledge, drugs can be used to alter the behavior of the ureter in an attempt to promote stone passage. Peristalsis has always been thought to be essential to allow stone passage and therefore it has been necessary to determine whether stone passage occurs by promotion of ureteral activity or by smooth muscle relaxation. Research indicates that drugs which allow continued peristalsis whilst preventing the increased uncoordinated activity seen in renal colic would be the most advantageous. The alpha-lA-adrenoceptor antagonists are the most effective drugs to date.