Effects of Anoxia on the Biphasic Response of Isolated Strips of Rabbit Bladder to Field Stimulation, Bethanechol, Methoxamine and KCI

Publisher Website
Google Scholar
Abstract
The contractile response of the bladder can be divided into two phases: an initial rapid increase in tension and a prolonged period of sustained tension (plateau phase). The bladder empties primarily during the plateau phase of the contractile response. These two phases can be differentiated using both pharmacologic and metabolic agents, indicating that the two phases have independent energy requirements. The present study compares the phasic (peak) and tonic (plateau) components of the responses of isolated strips of bladder body and base to field stimulation, bethanechol, methoxamine and KCI administration. New Zealand White rabbits were anesthetized with pentobarbital, and the bladder was removed. The bladder was divided between body and base at the level of the ureteral orifices. Three strips of bladder body and three strips of bladder base were mounted in separate baths containing Tyrode’s solution at 37 °C and equilibrated with 95 % 02, 5 % CO2. Anoxia was produced by changing the gas mixture to 95% nitrogen, 5% CO2. The effects of anoxia on the responses to field stimulation, bethanechol, methoxamine and KCI were determined at different times after the initiation of anoxia. The results of these studies can be summarized as follows: (1) Anoxia induced time-dependent decreases in both peak and plateau phases of the response to field stimulation (2 and 32 Hz). (2) The rate of inhibition of the plateau phase was significantly and substantially greater than that of the peak phase in both the bladder body and base. (3) Similarly, anoxia inhibited the plateau phase of the bladder body’s response to bethanechol to a significantly and substantially greater degree than anoxia inhibited the peak contraction. (4) Anoxia potently inhibited both the peak and plateau phases of the response of the bladder base to methoxamine. (5) Anoxia (15 min) produced only mild inhibitions of the peak and plateau phases of the responses to KCI. These studies demonstrate that the ability of the bladder to sustain increased tension following receptor-mediated contraction (field stimulation, bethanechol and methoxamine administration) is lost rapidly upon the initiation of anoxia, whereas the ability to generate peak tension is reduced gradually over a 30-min time period. Alternately, the bladder’s ability to both generate and sustain tension following KCI stimulation (non-receptor-mediated membrane depolarization) decreases along the same gradual time course as its peak response (inhibited by anoxia) to field stimulation and bethanechol administration. In conclusion, the ability of the bladder to sustain increased tension during a receptor-mediated contraction is dependent on oxidative metabolism. Since the bladder empties during the sustained phase of the response to stimulation, the ability of the bladder to empty (as compared to its ability to generate pressure) would be very sensitive to a reduction in oxidative metabolism.

This publication has 0 references indexed in Scilit: