Role of cyclic adenosine monophosphate in prostaglandin E₁-induced penile erection in rabbits

To investigate the role of cyclic adenosine monophosphate (cAMP) in penile erection in relation to the effect of prostaglandin E₁ (PGE₁), male adult New Zealand white rabbits were utilized as a model to study intracavernous pressure (ICP) in vivo. After intracavernous injection of PGE₁ (0.2-1.6 μg/kg) and 8-bromocyclic adenosine monophosphate (8-Br-cAMP, 0.5-1.5 mg/kg), both drugs raised the ICP in a dose-dependent manner. The increased ICPs induced by PGE₁ and 8-Br-cAMP were 33.4 ± 8.12 and 24.1 ± 4.9 mm Hg, respectively (p < 0.05, paired Student's t test). Administrations of cyclic adenosine monophosphothioate, Rp-isomer (cAMP antagonist, 0.02-0.08 μmol/kg) prior to PGE₁ injections inhibited the effect of PGE₁ in vivo in a dose-dependent manner. The systemic blood pressures and heart rates in rabbits were unchanged during all the intracavernous injections. The corpus cavernosal tissues isolated from rabbits were studied for the cAMP contents after incubation of different doses of PGE₁ in vitro. The cAMP contents were also elevated in a manner parallel with the increases in PGE₁ concentrations (3-9 μM). We conclude: (1) the feasibility of intracavernous injection of vasoactive drugs is similar to that in man, thus the rabbit can be used as a suitable alternative for the studies of penile erection, and (2) cAMP is mediated in PGE₁-induced relaxation of the rabbit corpus cavernosum, and the cAMP system only participates partially in penile erection.