The effects of urine on mast cells and smooth muscle of the human ureter.

Electron microscopy was performed on normal human ureteral rings before and after incubation in human urine for 30 minutes. A large number of mast cells was detected subepithelially and in close proximity to smooth muscle fibres. Treatment with urine (346 mOsm/l) induced various degrees of degranulation in the majority of mast cells. Some membrane bound granules were found free in the surrounding connective tissue and near smooth muscle cells indicating rupture of the cell membrane. In the functional study frequency and amplitude of peristaltic contractions were studied in-vitro. Addition of urine increased frequency and amplitude of peristaltic contractions and addition of the histamine-1-blocker mepyramine (10(-6) M) partially reversed these changes. It can be concluded that in a situation with urothelial damage such as ureteral calculus, urine can penetrate subepithelially and induce degranulation of mast cells with release of mediators. This is followed by forceful peristaltic contractions which are induced by histamine and other newly formed mediators such as prostaglandins. The process is likely to occur in renal colic with impacted kidney stones.