Objective: As the most common second massagers, cyclic guanosine 3, 5 monophosphate (cGMP) and cyclic adenosine 3,
5 monophosphate (cAMP) have widely confirmed to modulate
the contractility of smooth muscle in many tissues. However, the
documentation as to the contractility of SV is relatively sparse.
We examined the effects of vardenafil and caffeine on nervemediated
contraction and phenylephrine-induced contractures
to testify whether cGMP and cAMP are involved in modulating
the contractility of smooth muscles from seminal vesicle (SV).
Methods: Muscle strips were prepared from guinea-pig SV and
contractions were elicited by 3 s trains of electrical field stimuli
(0.1 ms, 10-100 Hz) or 0.1 M phenylephrine respectively.
Various concentrations of vardenafil (1, 3, 10 and 30 μM) and
caffeine (0.1, 0.3, 1, 3 and 10 mM) in a cumulative manner were
used to identify and characterize cGMP and cAMP.
Results: Both vardenafil and caffeine produced differential
inhibition on contractions at most stimulation frequencies,
and the inhibitive effect of vardenafil or caffeine significantly
increased with the improving of concentration. The half-maximal
inhibition concentration of vardenafil and caffeine at 40 Hz were
2.6±1.4 μM and 2.6±0.5 mM respectively. Additionally, caffeine
significantly inhibited the nerve-mediated contraction, and
when combined with vardenafil, the inhibitive effect of caffeine
was significantly enhanced. Moreover, there was no significant
difference of inhibitive rate between vardenafil and vardenafil on
the basis of the inhibitive effect of caffeine. Neither vardenafil nor
caffeine had effect on the phenylephrine-induced contracture
of smooth muscle from SV, and there was no significant change
with the increasing of the concentration.
Conclusions: The cGMP-specific phosphodiesterase and
cAMP-specific phosphodiesterase are present in intramuscular
nerve not smooth muscle itself, and cGMP and cAMP serve
as two main second massagers separately to modulate the
contractility of smooth muscle from SV. Abnormality in cGMP
and cAMP may lead to dysfunction of SV and hence contribute
to the mechanisms of premature ejaculation.