Modulation of detrusor contraction strength and micturition characteristics by intrathecal baclofen in anesthetized rats.

Abstract

The effect of intrathecal (i.t.) baclofen in modulating the micturition reflexes, detrusor contraction strength, and micturition efficiency was evaluated in anesthetized rats. Female Wistar rats (n = 14, 337 +/- 8 gm.) were anesthetized with urethane (1.2 gm./kg. s.c.). Cystometrograms were done through a lower midline incision made to expose the bladder and a catheter was inserted through the bladder dome to record pressure during filling with saline at the rate of 0.038 ml./min. During the micturition phase of cystometrogram, the measurement of voided volume was made synchronously with the intravesical pressure. Baclofen was given intrathecally at the increasing doses of 0.05, 0.10, 0.5 microgram. and pressure/flow parameters were measured. The measured urodynamic parameters show that baclofen produced a significant dose dependent increase in bladder capacity and a decreases in voiding efficiency, detrusor pressure and maximum and average flow rate. Baclofen (0.1 microgram.) significantly decreased detrusor contractility reducing both Wmax from 3.7 +/- 0.1 (control) to 2.0 +/- 0.1 W/m2 and Wisv,max from 5.9 +/- 0.3 to 5.5 +/- 0.4 W/m2 respectively. Baclofen altered the characteristic pattern of the micturition reflex by suppressing high frequency pressure oscillations during voiding which was completely abolished after 0.1 microgram. in 75% of the rats. Furthermore, urinary dribbling incontinence was evident at a dose of 0.5 microgram. in 58% of all rats. These results demonstrate that i.t. baclofen has a significant inhibitory effect on the micturition reflex, depressing detrusor contraction strength and micturition efficiency, while increasing bladder capacity.