Local suppressive effect of clonidine on penile erection in the dog

Neuroleptics induce penile erection in the rabbit

1. Intramuscular (i.m.) administration of the neuroleptics chlorpromazine, haloperidol and spiperone at doses ranging from 0.1 to 0.4 mg/kg in male rabbits induced a dose-dependent penile erection. 2. The i.m. administration of the alpha 1-adrenoceptor antagonists prazosin and bunazosin (0.1-0.4 mg/kg), induced a dose-dependent penile erection. However, that of the peripheral dopamine receptor antagonist domperidone (0.4-4.0 mg/kg) and the dopamine receptor agonist apomorphine (0.1-1.0 mg/kg) did not. Penile erection was not induced by i.m. injection of chlorpromazine in combination with intrapenile administration of the alpha 1-adrenoceptor agonist methoxamine. 3. Penile erection was induced by the administration of chlorpromazine (0.25-1.00 mg/body) into the lateral cerebral ventricle. At a low dose, however, the administration of chlorpromazine into the lateral ventricle induced a less notable penile erection than that induced intramuscularly. 4. Penile erection was induced by i.m. injection of the ganglionic blocker hexamethonium (5-20 mg/kg). When chlorpromazine was given after pretreatment with hexamethonium, penile erection was more notable than that induced by either drug given alone. 5. These results suggest that neuroleptics could act locally in the penile structure to cause penile erection by alpha 1-adrenoceptor-blocking actions.

Intracavernous pressure as an experimental index in a rat model for the evaluation of penile erection

This report communicates our attempt to design a small animal model for the evaluation of penile erection, based on the pharmacological responses of cavernous tissues in the rat that resemble those of human subjects. Male adult Sprague-Dawley rats anesthetized with pentobarbital sodium were used in conjunction with papaverine and prostaglandin E1, two vasoactive drugs most commonly used in clinical management of impotence. Intracavernous administration of papaverine (0.05, 0.1, 0.02, 0.4 or 0.8 mg.) induced a progressive increase in intracavernous pressure that peaked at 0.4 mg. This effect was associated with visible penile erection that became conspicuous when accompanied by additional bursts of transient intracavernous pressure fluctuations. The duration of papaverine-induced increase in intracavernous pressure was significantly shortened by clonidine (15 micrograms, intracavernous). Injection of prostaglandin E1 (1, 2 or 4 micrograms) into the corpus cavernosum also elicited an elevation in intracavernous pressure, but the responses exhibited acute tachyphylaxis. By manifesting a response to papaverine and prostaglandin E1 that is similar to that in human, we conclude that the intracavernous pressure in the rat may represent a suitable index for the evaluation of penile erection in small laboratory animals.

Castration may not affect the penile erection ability in terms of peripheral neurocavernous mechanism in dogs

The penile erection ability (PEA) was assessed in 27 dogs with intact orchids (Group I), seven dogs with bilateral orchidectomy for one month (Group II) and four dogs with bilateral orchidectomy for three months (Group III). PEA was indicated by the increase of the intracorporeal pressure (ICP) upon electrical stimulation of the cavernous nerves. PEA was significantly decreased in both orchidectomized groups. However, when reduction in the blood pressure was considered, the difference in PEA between Group I and the orchidectomized group was no longer significant. Before the orchidectomy, plasma testosterone level of 22 adult male dogs varied widely from 105 to 6302 pg./ml. At one or three months after the orchidectomy in 11 dogs, it decreased to a level below 100 pg./ml. There was no significant change in the body weight in the post orchidectomy period. These findings indicate that the castration and/or the resulting low plasma testosterone level does not directly affect PEA through the peripheral neural and cavernosal mechanism.