EFFECT OF ISOPROTERNOL ON BASAL TENSION OF ISOLATED RABBIT BLADDER SMOOTH MUSCLE

Abstract

It has been reported that there is big difference in response to isoproterenol between in vitro muscle strip and in vivo whole body. In order to resolve this problem, we have examined the difference in doseresponse, time-course and stretch-response to isoproterenol between the body and base of rabbit bladder.
We obtained the results that there was no qualitative difference in dose-response and time-course between these two regions and that stretching of the strips did not alter the effect of isoproterenol significantly. By these results, we can not explain the discrepancy of the potency between whole bladder and muscle strip. However, we have obtained the interesting result that the strips could be classified into stable and unstable, and stable strips responded to isoproterenol poorly, whereas unstable ones responded very strongly.
From this result, the difference in potency between whole bladder and muscle strip may be adequately explained: The potency and magnitude of the effect of isoproterenol on the urinary bladder is poor itself, as obtained in vivo and in vitro with whole bladder and stable muscle strips. However, in muscle strip study, the strips easily become unstable and the unstable strips respond to isoproterenol strongly.