Role of the trigone in micturition.

The exact function of the trigone in the act of micturition is not yet known. The current communication discusses its role. The myoelectric activity of the urinary bladder and trigone was studied in nine volunteers (six women, three men; mean age 38.6 +/- 9.9 years) using Beckman suction electrodes. Two electrodes were applied to the bladder and one to the trigone. The EMG and vesical pressure were recorded before and during vesical filling and voiding. Slow waves or pacesetter potentials (PPs) were recorded at rest from the detrusor and trigone. They had regular frequency and were followed randomly by bursts of action potentials (APs). The frequency and amplitude of the trigonal PPs and APs were significantly lower than those of the vesical tissue. The mean PP frequency was 5.8 +/- 1.8 cycle/min (cpm) and amplitude 0.69 +/- 0.1 mV in the bladder and 3.4 +/- 1.2 cpm (P < 0.05) and 0.36 +/- 0.09 mV (P < 0.05), respectively, in the trigone. During vesical filling, neither the vesical pressure nor the vesical and trigonal PPs and APs registered significant differences from the resting stage (P > 0.05). During voiding, the vesical electric activity increased and presented as fast activity spikes or APs of high amplitude (mean 678.6 +/- 88.6 muV). The trigonal electric activity showed no significant change (P > 0.05) in comparison with the pre-evacuation status. These findings suggest that the trigone does not contract during voiding, thus refuting the claim that the trigone is responsible for preventing ureterovesical reflux on voiding.