EFFECT OF ANOXIA ON THE URETHRAL RESPONSE TO PHENYLEPHRINE

Purpose: Smooth muscle requires oxygen for proper contractile function. In addition, anoxia has been shown to inhibit the contractile response to various forms of stimulation. Continence, at least in part, depends upon active alpha-adrenergic tone, which provides intraurethral tension during bladder filling. The current study was designed to determine the effect of anoxia on the ability of the urethra to sustain tension. Materials and Methods: Standard isolated urethral strip preparations were used to determine the effect of anoxia on the contractile response to phenylephrine; isolated whole urethra preparations were used to determine the effect of anoxia on the intraurethral pressure-flow characteristics. Results: The peak tension responses of the female and male urethra to phenylephrine were significantly greater than the plateau tension. Anoxia induced an immediate decrease in phenylephrine-stimulated tonic tension to baseline tension. In the whole urethra preparation, phenylephrine increased opening pressure to a greater extent in the male urethra than in the female urethra. In both sexes, anoxia reduced the opening pressure and completely prevented phenylephrine stimulated increases in opening pressure. Conclusion: The tonic response to phenylephrine is lost virtually immediately upon the initiation of hypoxia. This suggests that hypoxia decreases the ability of the urethra to maintain a tonic response to alpha-adrenergic stimulation during bladder filling and may be a factor in incontinence, especially in females.