The ejaculatory mechanism involves 2 reflexes: the "glans-vasal," which see
ms to bring the semen to the posterior urethra (emission phase of ejaculati
on), and the "urethromuscular" which ejects it to the exterior (ejection ph
ase). This study investigated the mechanism of bulbocavernosus muscle (BCM)
contraction, once the seminal fluid reaches the bulbous urethra. The study
included 14 healthy male volunteers (mean age 37 +/- 10.2 SD years). To te
st the response of the BCM to urethral distension, a 10F balloon-tipped cat
heter was introduced into the prostatic urethra and filled with saline in i
ncrements of 0.25 mt: a needle electrode recorded the response. The balloon
was then withdrawn to lie in the membranous, bulbous, and pendulous urethr
a and the test was repeated at each sire. The latency of the muscle respons
e was calculated. The BCM response to each of the anesthetized bulbous uret
hra and anesthetized BCM was recorded. Distension of the prostatic, membran
eous, or pendulous urethra effected no BCM EMG response. Bulbous urethral d
istension with 0.25 mt of saline also produced no muscle response. whereas
distension with 0.5 mL and up to 1.5 mL caused increased EMG activity of th
e BCM. The muscle response augmented with the increase of the distending vo
lume. The mean latency was 10 +/- 1.3 ms and showed no significant change (
p >.05) with the different distending volumes. Neither the anesthetized bul
bous urethra nor the anesthetized BCM responded to bulbous urethral distens
ion. The BCM contraction upon distension of the bulbous urethra is probably
reflex and mediated through the urethrocavernosus reflex. Small-volume dis
tension did not effect BCM contraction. The latter presumably propels the s
emen from the posterior to the pendulous urethra. It is suggested that the
urethrocavernosus reflex be included in current andrologic investigations f
or patients with ejaculatory disorders.