Aims of Study
Because all three components of lower urinary tract control(parasympathetic, sympathetic and somatic) are intimately associated with serotonin(5-HT) and norepinephrine(NE) containing terminals and receptors, in the present study, we exmained the effects of increasing extracellular levels of 5HT and NE with venlafaxine, a serotonin and norepinephrine reuptake inhibitor, on lower urinary tract function in rat.

Methods
Urethral perfusion pressure and isovolumetric bladder pressure were measured with catheters inserted through the bladder dome in anesthetized female SD rats(250-300 gm., n=20). The catheter assembly was seated securely in the bladder neck to block passage of fluid between the bladder and urethra. The external urethra was not catheterized. Responses were examined in saline perfusion through the urethra ( perfusion speed of 0.007 ml/min). Simultaneous bladder and urethral pressure recordings were made at the control state and after the intraarterial (i.a.) injections of target drugs. Drugs injected were as followed; phenylephrine(10-100uM), phentolamine(10-1000uM), paroxetine(10-100uM), venlafaxine(100uM).

Results
During isovolumetric bladder contraction, urethral pressure was decreased simultaneously, and then returned to the resting states in conjunction with the end of the bladder contraction. Intraarterial injection of phenylephrine increased amplitutde of urethral perfusion pressure significantly without obvious changes of bladder pressure. Micturition frequency and urethral pressure were significantly decreased after i.a. injections of phentolamine. Injections of paroxetine did not cause significant changes of the bladder or urethral pressure. Administration of venlafaxine caused a significant increases of urethral pressure (p<0.01). Magnitude of the urethral pressure increment was not significantly different between phenylephrine and venlafaxine.

Conclusion
These results suggest that venlafaxine, which has been widely used in the treatment of depression, may be also useful in the management of stress urinary incontinence by increasing urethral pressure.