LENGTH-TENSION CHARACTERISTICS IN CHRONICALLY OBSTRUCTED DILATED URETER

Abstract

A rabbit model with partial obstruction for 50-150 days was experimentally produced. The mechanical properties of smooth muscle strips from the helical layer of obstructed rabbit ureter was studied under isometric condition. In order to tetanize the muscle of normal and dilated ureter, 40V, 50Hz, a-c stimulation was used at 37°C with oxygenated Krebs-Ringer's solution.
Active and passive length-tension characteristics of the normal and dilated ureter were determined. Developed force increased with elongation up to a maximum and then decreased with further lengthening as in skeletal muscles. Passive tension increased more rapidly with length change in dilated ureter than normal ureter.
In responses of 7 dilated ureters to relative strain (ΔL/Ls), the passive tension of 4 obstructed ureters was higher than that of nomal ureter. These 4 ureters had been obstructed for over 100 days after obstruction.
Moderately obstructed ureters were capable of exerting a larger force per unit cross sectional area of muscle. But, in severely obstructed ureters, the maximum active tension was less than normal ureter. With 8 dilated ureters, the maximum active tension was decreased with increase in degree of dilatation. A significant correlation was demonstrated between the maximum active tension and the degree of dilatation.