Length density and total length of acetylcholinesterase positive nerves related to cystometry and in vitro studies of muscle strips in mini-pig urinary bladder after chronic outflow obstruction and recovery from obstruction.

Chronic partial bladder outlet obstruction was created in mini-pigs by implanting a 6-7 mm ring around the proximal urethra. After a median obstruction period of 63 days, the ring was removed and after a median recovery period of 60 days the animals were sacrificed. At each occasion stepwise cystometry, measurement of residual urine, muscle strips studies with electrical and carbachol stimulation, and stereological estimations of length density and total length of acetylcholinesterase positive nerves were performed. The results can be summarized as follows: (1) unchanged sensitivity of muscle strips to carbachol, but markedly decreased contractility and rate of contraction to carbachol, (2) no evidence of detrusor instability, but severely decompensated bladders in two pigs, (3) a significant increase in residual volume, (4) a pronounced decrease in length density and total length of acetylcholinesterase positive nerves, and (5) at field stimulation strips from some pigs showed increased sensitivity and contractility with high atropine and TTX resistance, while strips from the other pigs revealed decreased sensitivity and markedly decreased contractility to electrical stimulation. In general, most of the changes were markedly, though incompletely, reversed after recovery. Light and electron microscopy of muscle strips showed no histological or ultrastructural changes during the experiments or after storing 1 day at 4 degrees C.