The response of the corporal tissue and cavernosus muscles to urethral stimulation: an effect of penile buffeting of the vaginal introitus.

We investigated the hypothesis that urethral stimulation in humans induces sexual response in the form of activation of the corporal tissue and cavernosus muscles through a reflex mechanism. Electromyographic activity of corpora cavernosa (CC), corpus spongiosum (CS), bulbocavernosus (BCM), and ischiocavernosus (ICM) muscles was recorded in 43 healthy volunteers (24 men, 19 women; age, 37.7 +/- 8.2 years) during urethral stimulation. The tests were repeated after individual anesthetization of urethra, CC, CS, BCM, and ICM. During stimulation of the distal urethra, slow wave variables of CC and CS decreased while motor unit action potentials of BCM and ICM increased. Urethral stimulation after individual anesthetization of urethra, CC, CS, BCM, and ICM did not effect significant changes in these structures, but saline administration did. Diminished electromyographic activity of CC and CS with increased activity of BCM and ICM during distal urethral stimulation presumably denotes sinusoidal muscle relaxation of CC and CS and cavernosus muscles' contraction. Sinusoidal muscle relaxation and contraction of cavernosus muscles upon distal urethral stimulation are suggested to be mediated through a reflex that we call the "urethro-corporocavernosal reflex." Sinusoidal and cavernosus muscles' response during coitus appears to effect a degree of tumescence for both male and female partners.