Is abdominal wall contraction important for normal voiding in the female rat?

Area of Science:

• Urology
• Physiology
• Neuroscience

Background:

• Normal voiding in rats involves abdominal wall muscle contraction, similar to the visceromotor response (VMR).
• This abdominal activity may be crucial for generating the bladder pressure needed for efficient, pulsatile urine release.

Purpose of the Study:

• To investigate the presence and necessity of abdominal wall activity during normal voiding in urethane-anesthetized female rats.
• To differentiate this physiological response from the VMR to noxious stimuli.

Main Methods:

• A free-voiding model was used in rats without instrumentation to assess abdominal wall EMG during physiological bladder filling.
• Rectus abdominis EMG and uroflow parameters were measured before and after inducing paralysis of these muscles using botulinum-A (BTX).

Main Results:

• Abdominal wall muscle activity was observed during normal free voiding.
• BTX-induced paralysis abolished this activity, significantly decreasing average per-void volume (1.8 to 1.1 ml) and average flow rate (0.17 to 0.11 ml/sec).
• The intercontraction interval remained unchanged.

Conclusions:

• The Voiding-associated Abdominal Response (VAR) is a necessary component of normal voiding in this model.
• VAR may ensure efficient voiding by contributing to bladder pressure, potentially initiated by signals from the proximal urethra.
• The term VAR is proposed to distinguish this normal voiding response from the VMR.