The influence of filling rates and sympathectomy on bladder compliance in the chloralose‐anaesthetised cat

The effect of total sympathectomy (hypogastric nerve and sympathetic chain section) on the relationship between bladder compliance and filling rate has never been studied over the full range of physiological filling rates. In a series of chloralose‐anaesthetised cats, we examined the effect of total sympathectomy on bladder stiffness (the inverse of compliance) at filling rates from 1 to 50 hourly diuresis (HD) units. In control animals the slopes of regression lines fitted from 5 to 30 (n = 7) or 5 to 50 (n = 3) HD units were equal to or approached 0 (mean slope = .002 ± .0008 SE). After sympathectomy there was a statistically significant increase in stiffness at filling rates from 5 to 30 HD units (P < .005), and, although there was a trend for increased stiffness at higher filling rates, the increase in the slopes of the regression lines did not reach statistical significance (.05 < P < .1). The volume threshold for micturition at a filling rate of 5 HD units was significantly lowered after sympathectomy (P ≤ .0005). We conclude that the sympathetic nervous system makes a significant contribution to the control of bladder stiffness (and therefore compliance) within the range of physiological filling rates and that this effect may be more important at higher rates of filling. The sympathetic nervous system also has a role in determining the volume threshold for micturition at physiological filling rates.