Structural changes in the rat bladder after acute outlet obstruction.

The urinary bladder of adult female rats was subjected to complete outlet obstruction for periods of up to 24 h. Within 2 h the obstruction led to a rise in intravesical pressure to about 80 mmH2O. Subsequently, the pressure remained high but declined slightly. After 24 h of complete obstruction the bladder was maximally distended, but its volume was similar to that of a control bladder fully distended, indicating that overstretch (or overdistension) occurs only to a very limited degree. After 6 h of obstruction there was congestion of all the intramural blood vessels and extravasation of red blood cells from some vessels of the mucosa. At 12 h and 24 h the extravasation was very substantial and there was also infiltration of erythrocytes in the muscle layer. Ultrastructurally, there were several damaged nerve endings (but no changes in the nerve trunks) and, occasionally, damaged muscle cells. Removal of the obstruction after 24 h was followed by resorption of the extravasate, partly by phagocytosis by muscle cells, a process which lasted 4-6 days, and by 7 days damaged varicosities and muscle cells became uncommon. We conclude that the changes observed in the bladder wall following complete obstruction are caused more by haemorrhage and ischaemia than by overstretch and that the changes are reversed when outlet conditions are normalized.