URETHRAL PRESSURE RESPONSE TO SMOOTH AND SKELETAL-MUSCLE RELAXANTS INANESTHETIZED, ADULT MALE CATS WITH NATURALLY ACQUIRED URETHRAL OBSTRUCTION

The effects of the skeletal muscle-relaxing dug dantrolene sodium alon e, and in combination with the alpha(1)-adrenergic antagonist prazosin , on the urethral pressure profile were investigated in male cats with obstructive lower urinary tract disease. Decreases in mean segmental intraurethral pressure induced by dantrolene (n = 3) or dantrolene in combination with prazosin (n = 3) were evaluated statistically, using a paired design. Statistical analysis was applied to absolute (mm of H g) pressure values. Intravenous administration of dantrolene alone (1 mg/kg of body weight, n = 3) significantly decreased pressure in the p ostprostatic/penile urethral segment, but did not decrease prostatic u rethral pressures. Dantrolene in combination with prazosin (0.03 mg/kg , IV) caused a 20% pressure decrease in the prostatic segment (P = 0.0 60). Preprostatic urethral pressure was not significantly affected by either treatment regimen in the small pool of cats studied. There was no difference in baseline pressures (mm of Hg) in the 3 Intraurethral segments of these 6 recently obstructed male cats, compared with histo ric baseline pressures (mm of Hg) in the 3 intraurethral segments of 2 8 healthy male cats. These results indicate that dantrolene and prazos in may be effective in relaxing intraurethral skeletal and smooth musc ulature in male cats clinically afflicted with obstructive lower urina ry tract disease. However, it is not certain that administration of mu scle relaxants would facilitate urethral catheterization and removal o f the obstruction in male cats with blockage of the lower urinary trac t. Strikingly, results of this study suggest that urethral muscle spas m had a minor role in these cats.