Motility of the Urinary Bladder in Cats During Filling at Physiological Rates

Abstract

Spontaneous rhythmic bladder contractions were studied in conscious and anesthetized cats. Rhythmic activity was absent in the awake state, but appeared during deep relaxation or sleep. Usually, marked rhythmic bladder activity was present in the anesthetized cat, showing a differentiated reaction to distension. In response to physiological filling rates and various bladder volumes the spontaneous rhythmic contractions of the intact bladder had a frequency of 1-4/min, amplitudes up to 20 cm H₂O (majority between 5-15 cm H₂O) and a duration of 10-20 sec. The smallest increase in the rate of filling necessary to cause a rise in frequency was 0.08 ml/min (~1.5 hour-diuresis). When the entire collecting phase was recorded during a gradual rise in filling rate, a typical pattern often occurred. The first response of the rhythmic contractions was a rise in amplitude followed by increased frequency. Towards the micturition the amplitude decreased while the frequency continued to increase. The volume threshold of appearance of the contractions was variable and unpredictable, and micturition occurred also without a significant preceding pattern of the rhythmic activity. Transection of the spinal cord above the segments of autonomic nervous outflow to the bladder (above Th₁₀) did not alter rhythmic contractions permanently. After partial or complete extrinsic denervation of the bladder the rhythmic contractions either disappeared or occurred with a frequency of 3-5/min, amplitudes less than 6 cm H₂O and a duration of 10-20 sec. The contractions became irregular and showed no significant reaction to bladder distension. Thus, the differentiated reaction of the spontaneous rhythmic contractions to distension is dependent on intact bladder innervation from the spinal cord.