The peno-motor reflex: study of the response of the puborectalis and levator ani muscles to glans penis stimulation.

The response of the pelvic floor muscles (puborectalis 'PR' and levator ani 'LA') as well as the vesical, prostatic urethral and anal pressures to glans penis 'GP' stimulation was determined aiming to elucidate their role in the sexual act. The study was done in 16 healthy volunteers (mean age 43.3 years). The GP was stimulated mechanically and electrically by surface electrode. The vesical and prostatic urethral pressures were measured with a two-channel microtip catheter and the anal pressure by a balloon-tipped catheter. The response of the PR and LA muscles to GP stimulation was determined by a needle electrode inserted into each of them. Upon electrical or mechanical stimulation of the GP, the vesical pressure showed significant drop (p < 0.05), whereas the prostatic urethral and anal pressures increased (p < 0.05). The EMG of the PR and LA muscles recorded significant increase (p < 0.01). The response was greater upon electrical than mechanical stimulation and was not evoked by stimulation of either the anesthetized GP or the PR and LA muscles. PR and LA contraction upon GP stimulation postulates a reflex relationship which we call 'peno-motor reflex'. The constancy of this reflex relationship is evidenced by reproducibility and by the failure to evoke the response when either of the two arms of the reflex arc was anesthetized. PR contraction is associated with contraction of external urethral, prostatic and anal sphincter which might explain the rise of prostatic urethral and anal pressures. It seems that during the sexual act urethral and anal sphincters' contraction prevents leak of urine or stools, while prostatic sphincter contraction squeezes the prostatic secretions into the posterior urethra.