Characteristics of spontaneous contraction and effects of isoproterenol on contractility in isolated rabbit renal pelvic smooth muscle strips.

The contractile characteristics and the contractile responses to isoproterenol were examined by measurement of the isometric force in three types of smooth muscle strips obtained from the upper and lower parts of the renal pelvis and longitudinal strips encompassing the entire length of the renal pelvis. Regular rhythmic contraction was recorded from the upper renal pelvic strip with a frequency of 8.4 +/- 0.9 times per minute and from the lower renal pelvic strip with a frequency of 2.3 +/- 0.4 times per minute. The contractile frequency in the whole pelvic strip encompassing the entire longitudinal length of renal pelvis was found dependent on that in the upper renal pelvic strip. Isoproterenol caused an increase of contractile force in the upper pelvic strip and a decrease in the lower pelvic and whole pelvic strips. The results seem to suggest that the smooth muscle of the upper part of the renal pelvis is distinct from other smooth muscles and resembles heart muscle in its contractile response to isoproterenol.