Relevance of Spontaneous Activity to Urinary Bladder Function: An in Vitro and in Vivo Study

Abstract

The presence and functional significance (if any) of spontaneous activity in the normal urinary bladder during filling is a controversial subject. One model used by many investigators to study spontaneous activity has been isolated urinary bladder smooth muscle strips. Although spontaneous activity is a property commonly observed in isolated urinary bladder strip preparations, the in vitro whole bladder preparation (rabbit) is devoid of spontaneous activity. Additionally, under normal conditions the in vivo rabbit bladder does not display spontaneous activity during the filling phases of micturition. The present study compares the spontaneous activity of isolated smooth muscle strips, the whole bladder preparation, and the catheterized in vivo bladder (rabbit). The results are as follows: The spontaneous activity (frequency and amplitude) of isolated strips is extremely variable among strips of the same bladder. Spontaneous activity is not affected by the following specific inhibitory compounds: tetrodotoxin, atropine, phentolamine, propranolol and hexamethonium. This indicates that spontaneous activity observed in isolated strips is myogenic in nature and not dependent on the activation of specific autonomic receptors. The in vitro whole bladder preparation shows no spontaneous activity at any volume or pressure unless longitudinal tension is applied. The spontaneous activity of the whole bladder subjected to longitudinal tension is not affected by the same compounds mentioned above. Spontaneous activity of the in vivo bladder is absent at low intravesical volumes and pressures. Spontaneous activity develops upon reaching a critical pressure. However, this activity is completely inhibited by intravenous ganglionic blockade (hexamethonium). In the presence of hexamethonium, the in vivo bladder is devoid of spontaneous activity at any volume or pressure, thus the in vivo "spontaneous activity" is mediated through neuronal reflexes. It is concluded that under normal circumstances the rabbit bladder is devoid of myogenic spontaneous activity and that the spontaneous activity observed in isolated strips is directly related to longitudinal stretch. Since under normal conditions the bladder is not subjected to longitudinal stretch, the spontaneous activity observed in the isolated strip studies has little physiological significance under normal conditions, but could help explain the pathophysiology of certain dysfunctions during the filling stage of micturition.

New concepts in relation to urge and detrusor activity

“…The results obtained from similar experiments on human unstable bladders are consistent with this observation in vitro. Our results show that spontaneous activity observed in vitro is more than an artifact, as was concluded by Levin et al [1986]. Phasic spontaneous pressure waves may be induced by blockwise straining of the bladder wall.…”

Mechanical properties of mammalian single smooth muscle cells III. Passive properties of pig detrusor and human a terme uterus cells

“…In those cases where (small) wavelike increments of force were superimposed on the relaxation curves, the delay between the stretch and the onset of a superimposed force rise varied from at least 10--30 s, probably indicating a stretch induced cell depolarization, which gave rise to an additive active force component on the passive relaxation curve. In intact bladder muscle, and in bladder strips, the effects of stretch activated cell depolarization leading to force increases by cross-bridge cycling, were observed approximately 40--60 s after rapidly stretching the muscle (Levin et al, 1986;Van Mastrigt, 1977). The resulting wave-like superimposed force increments on the relaxation curve did not affect the general form of the relaxation curve to a significant degree (Coolsaet, 1975b).…”

Influence of Papaverine on Rat Bladder Contractions in vivo

“…Spontaneous rhythmic bladder contractions due to urethra ligation may represent a micturition reflex [11], However a fluid-induced stretching of the bladder wall may also be related to bladder contraction [12]. This activity can be completely inhibited by ganglionic block ade [8], The three kinds of bladder contractions we observed -a rhythmic spontaneous, a pelvic nerveinduced and a similar, but spontaneously exhibited single contraction -seem to be mediated through neuronal reflexes.…”

“…A spontaneous activity is known from bladder muscle strips [7,8]. In vivo, outlet obstruction induces a high degree of spontaneous contractile activity of the bladder [9,10].…”