EFFECTS OF ISOPROTERENOL ON CONTRACTILE FORCE AND CHARACTERISTICS OF SPONTANEOUS CONTRACTILE ACTIVITY IN ISOLATED RABBIT RENAL PELVIC SMOOTH MUSCLE STRIPS

Abstract

The characteristics of spontaneous contractility in isolated rabbit renal pelvis in response to isoproterenol are examined. Isometric studies are done on upper and lower renal pelvic muscle strips dissected radially as well as on whole segment which is dissected longitudinally to include both upper and lower pelvic muscles. Control study without the administration of isoproterenal shows a higher contractile frequency in upper pelvic muscle (8.4±0.9m^-1) than in lower pelvic muscle (2.3±0.4m^-1). Isoproterenol causes a concentration dependent increase in contractile force of upper renal pelvic smooth muscle. Conversely, isoproterenol causes a concentration dependent decrease in contractile force of lower renal pelvic smooth muscle. The contractile force of longitudinal whole muscle strip decreases in response to isoproterenol.
These data show that upper pelvic smooth muslce, which is thought to be a pacemaker region of pelviureteral peristalsis, has a contractile response to isoproterenol similar to that of cardiac musice and that the contractile response of lower pelvic muscle to isoproterenol is similar to that of the ureter and other smooth muscles.