Which mechanism describes how nifedipine or tamsulosin aid distal ureteral stone passage?

• A. Increasing urine calcium excretion
• B. Narrowing ureter
• C. Inducing ureteral dilatation and relaxation
• D. Decreasing peristalsis

Answer: (C)

Relaxing the smooth muscle of the ureter to widen the lumen makes it easier for a distal ureteral stone to pass. Tamsulosin blocks alpha-1 receptors in ureteral smooth muscle, reducing tone in the distal ureter, while nifedipine (a calcium channel blocker) lowers intracellular calcium in smooth muscle, causing further relaxation. The resulting ureteral dilation lowers resistance to flow and helps peristaltic movement push the stone toward the bladder. Increasing urine calcium excretion wouldn’t directly aid passage, narrowing the ureter would hinder it, and decreasing peristalsis would slow transit—so the key mechanism is ureteral dilatation and relaxation.