Mechanism of Penile Erection in the Dog

Abstract

A pressure-flow study of the corpus cavernosum penis in the dog was performed during the flaccid, tumescent, erect and rigid stages. Perfusion was selectively made into the penile deep artery. The erect stage was induced with the local administration of papaverine hydrochloride, and the rigid stage by electrostimulation of the ischiocavernous muscle during the erect stage. Concurrently, vascular casts of the penis at each stage of erection were observed under a scanning electron microscope for the anatomical analysis of the mechanisms controlling cavernous pressure. In the pressure-flow study, it was demonstrated that a combination of decreased arterial resistance and restricted venous outflow was essential to both cause and maintain the erect state. The rigid stage was generated by contraction of the ischiocavernous muscle tightly compressing the crus penis. In the rigid stage, the cavernous pressure was elevated as high as five times the perfusion pressure; nevertheless, no backflow from the cavernous sinus to the deep artery was recognized. By use of the casts, it was confirmed that venous outflow restriction in the erect and rigid stages was due to compression of the postcavernous venules and penetrating veins in the tunica albuginea. The deep artery was occluded in the tunica albuginea in the casts made during the rigid stage, suggesting that the backflow from the corpus cavernosum penis to the deep artery was prevented by this occlusion. Therefore, in the rigid stage, the arterial and venous occlusion isolated the cavernous sinus from the systemic circulation; this mechanism seems to account for the maintenance of the extremely high cavernous pressure.

Mechanism Preventing Backf low from the Canine Corpora cavernosa to Arteries in the Rigid Phase of Penile Erection

“…According to the method used in a previous study [5], the bul bourethral artery, the penile dorsal artery and the penile deep artery were exposed after removing the pubis and a part of the ischium. A polyethylene cannula (0.25 mm caliber) for recording the blood pres sure was placed in the deep artery via the dorsal artery, its tip being about 0.5 cm distal to the tunica albuginea.…”

“…This method of papaverine administration was based on the concept that the relaxation of both vascular smooth muscles and tra becular smooth muscles is responsible for the increased arterial inflow in erection [ 13], The rigid phase, in which the corporeal pressure is higher than the systemic pressure, was induced by the electrostimulation (1.5 V, 40 Hz) of the ischiocavernous muscle with an electrode put on the muscle [5], During the rigid phase, the deep artery' was transiently ligated at its most proximal point -as shown in figure 1 -in order to close the space between the cannula and the arterial wall. After dis connecting this cannula from the pressure transducer, we examined whether or not a backflow from the ligated cannula was present in the rigid phase.…”

“…We used a selective perfusion system of the deep artery [5] to obtain tissue materials fixed in the flaccid, tumescence/full erection and rigid phases as shown in figure 2. A polyethyl ene cannula was placed into the penile artery and ligated with this vessel.…”

“…The saline in the corpus cavernosum was then replaced by the fixa tive via the 18-gauge butterfly needle directly inserted into the corpus cavernosum, as there was little inflow to the corpus cavernosum via the deep artery in the full erection phase [5,14]. Immediately after the injection of the fixative, the proximal corpus cavernosum was mechanically compressed at least for 20 min to retain a high corpo real pressure above 350 mm Hg( fig.…”

“…I n dogs, for example, the peak of the corporeal pressure during erection was recorded to reach more than 5,000 mm Hg [1], The corporeal pressure in humans was recorded to rise at least ten times higher than the systemic pressure [4], In order to achieve such a pressure gradient, the corpus cavernosum must be isolated from the systemic circula tion by the obstruction of vessels both supplying and draining the corpus cavernosum. Many studies using morphological and physiological techniques have re vealed the mechanism of venous obstruction [5][6][7][8][9][10], In contrast, there have been only a few studies concerning the mechanism of arterial occlusion. Beckett et al [11] using antegrade serial angiography suggested that the internal pudendal artery or the penile deep artery might be mechanically occluded in rigid erection.…”