New evidence for prostaglandin induced motility of the ureter.

In the search for particular ultrastructural features which could be responsible for the persistent rhythmic contractility in sheep ureteral preparations we detected a large number of extracellular electron dense granules in the lamina propria of the ureter. These structures are very similar to lipid granules previously described in the renal papilla of the rat and man. Ureteral motility is blocked by indomethacin and prostaglandins are powerful stimulators of rhythmic contractions. Tissue extracts from the ureter contain substances which exhibit smooth muscle stimulating properties as shown in bioassays. Evidence is presented which shows that the ureteral granules contain lipid material which could be the source (precursor) of smooth muscle stimulating factors, probably prostaglandins.