Sympatholytic effect on striated urethral sphincter. A peripheral or central nervous system effect?

Area of Science:

• Urology
• Neuropharmacology
• Physiology

Background:

• Sympatholytic drugs are used to treat voiding disorders.
• The mechanisms by which these drugs affect urethral and anal sphincter function are not fully understood.
• Investigating the role of central versus peripheral effects is crucial.

Purpose of the Study:

• To investigate the effects of centrally acting and peripherally acting sympatholytic drugs on urethral pressure and sphincter electromyography.
• To determine if these drugs affect reflex-induced sphincter activity.
• To elucidate the potential central nervous system contribution to the efficacy of sympatholytic drugs in voiding disorders.

Main Methods:

• Intravenous administration of clonidine (crosses blood-brain barrier) and phentolamine (does not cross blood-brain barrier) to five healthy women.
• Measurement of urethral pressure and electromyographic activity of urethral and anal sphincters.
• Assessment of drug effects during bladder filling and voluntary pelvic floor muscle contraction.

Main Results:

• Clonidine significantly decreased urethral pressure and sphincter electromyography.
• Phentolamine decreased urethral pressure but did not affect sphincter electromyography.
• Neither drug inhibited reflex-induced increases in urethral pressure or sphincter activity.
• Phenoxybenzamine produced effects similar to clonidine.

Conclusions:

• Sympatholytic drugs that penetrate the blood-brain barrier exert effects on both urethral pressure and sphincter electromyography, likely via central mechanisms.
• Peripherally acting sympatholytic drugs primarily affect urethral pressure without impacting sphincter electromyography.
• Central effects on the striated urethral sphincter innervation may contribute to the clinical benefits of certain sympatholytic drugs in managing voiding disorders.