Obstruction induced changes in longitudinal force-length relations of rabbit ureter.

The force-length relationships of rabbit ureters subjected to 2 weeks of obstruction were compared with those of normal rabbit ureters. After 2 weeks of ureteral obstruction, length increased by 24 per cent, diameter by 100 per cent, and cross-sectional muscle area by 248 per cent. At the in vivo length, the resting forces of the control and obstructed ureters were similar. With muscle lengthening, resting force increased. For the same per cent increase over in vivo length, both control and obstructed ureters exhibited the same resting forces. At the in vivo length, the obstructed ureter developed less active force and less stress in response to a suprathreshold electrical stimulus than did control ureters. At the length of maximum force development (1.4 times the in vivo length for both control and obstructed ureters), the force developed by the obstructed ureter was 3.5 times greater than that of the control, yielding a 250 per cent increase over control levels. Thus, active stress (force/unit area) was unchanged after 2 weeks of obstruction.