Lower urinary tract dysfunction (LUTd) comprises multiple prevalent conditions of which many have a high impact on patient’s health and mental condition.  Current treatments often lack efficacy or come with bothersome side effects.  Animal models of lower urinary tract dysfunction are an important tool for preclinical drug development. Cystometry is widely accepted as the standard technique for studying bladder function in rodents. This technique allows the measurement of bladder pressure and voided volume during multiple filling and voiding cycles. During cystometry, the animals can be awake but are mostly anesthetized. The most frequently used anesthetic during cystometry is urethane, as it generates a long and stable anesthesia and as it does not abolish reflex voiding. Using a new technique called videocystometry, combining cystometry with continuous bladder imaging, we were able to continuously determine absolute bladder volume in addition to bladder pressure. Using this new technique, we determined the effect of urethane anesthesia on volume parameters such as residual volume, bladder capacity and urine flow.

Videocystometry was performed on 5 C57Bl/6J female mice (n = 5). During the experiment, the bladder was filled with saline supplemented with an iodine-based contrast agent, while placing the animal in a fluoroscope. Images were taken continuously at a framerate of 30 frames per second. Afterwards, bladder volume was determined based on the image data. Videocystometry was performed at increasing doses of subcutaneously administered urethane, starting with 0 g/kg bodyweight and adding 0.3 g/kg until a cumulative dose of 1.2 g/kg was reached. At each dose interval, videocystometry was performed during 40 minutes. For each urethane dose, pressure and volume data were later analyzed using repeated measures one-way ANOVA at a 0.05 significance level.

Urethane anesthesia at increasing doses does not affect voiding peak pressure or bladder capacity. The anesthetic does however induce a significant drop in voiding efficiency, which is dose-dependent with a mean voiding efficiency of 97% in animals who did not receive urethane, compared to a mean voiding efficiency of 45% in animals receiving a dose of 1.2 g/kg (p < 0.0001). Due to this drop in voiding efficiency, bladder residual volume increases with urethane dose. In animals receiving no urethane versus 1.2 g/kg urethane, the mean residual volume was 6 µl and 99 µl respectively (p < 0.0001) (figure 1). Importantly, urethane induces a dose-dependent reduction in maximal urethral flow rate and urethral conductance.

Urethane is a commonly used anesthetic during in vivo cystometry in rodents. Although it is known to spare reflex micturition, its mechanism of action is not clearly understood. We investigated the dose-related effect of urethane on different volume and pressure related voiding parameters. Our results show that although urethane does not completely suppress reflex micturition, it does have a clear dose-dependent effect on voiding efficiency, which causes a substantial increase in residual volume with each increase in urethane dose. This decrease in voiding efficiency can be explained by the dose-related decrease in urethral conductance. The above findings suggest that urethane anesthesia causes an impaired bladder-bladder outlet coordination during voiding.

The use of urethane as an anesthetic during cystometry has a dose dependent effect on bladder function by reducing voiding efficiency and increasing residual volume. These effects should be taken into account when interpreting in vivo experiments using urethane anesthesia.