Clinical observations suggest that cigarette smoking impairs erectile function in patients with moderate arterial insufficiency. To evaluate the effects of smoking on the physiology of erection, we studied six healthy adult mongrel dogs in which bipolar cuff electrodes were implanted around the cavernous nerves. After threshold stimulation parameters for penile erection were established, cigarette smoke collected in a 60-ml. syringe was released slowly near the dog's mouth, to be inhaled by natural breathing. Stimulation of the cavernous nerve was repeated and blood samples for nicotine, cotinine and blood gases were obtained before and after each cigarette. The systolic and intracorporeal pressure, flow through the internal pudendal artery, and venous flow from the corpora cavernosa were recorded at baseline and with each electrostimulation after smoke inhalation. Five of the six dogs were unable to achieve full erection after inhalation of smoke from two to three cigarettes. Some decrease of flow through the internal pudendal artery occurred and the venous restriction ability was almost completely abolished by smoking. Further, when nicotine was injected intravenously into two additional dogs, the same phenomenon was observed. These findings support the idea that cigarette smoking may contribute to impotence in some patients.

To elucidate the hemodynamic changes during erection, we measured corporeal blood gases in 6 monkeys before, during, and after erection induced by either papaverine or phentolamine or a combination of the two. Papaverine alone caused a strong erection (maximal tumescence and rigidity) by means of a rapid, large increase in pO₂ and pCO₂ with a pH drop to the acidic range. Phentolamine alone caused ‘delayed’ tumescence with less rigidity; the intracorporeal pO₂ level increased, but pCO₂ and pH values did not change significantly. The combination of both drugs offered no advantage over papaverine alone. We conclude that papaverine is a potent erection-inducing drug that acts in a bimodal manner, namely, it increases the arterial inflow and, at the same time, decreases the venous outflow. Phentolamine affects the arterial component of erectile function only.

To investigate the effect of chronic papaverine treatment, seven monkeys underwent repeated intracavernous injections for one year. One monkey died after 56 injections; the others received a total of 100 each. The strength and duration of erection were recorded after each injection, and the erectile tissue was examined histologically at the end of the study. Over the long term, papaverine maintains its erection-inducing capability, but it does cause pathologic changes in the erectile tissue: minimal to marked fibrosis at the injection site and hypertrophy of smooth muscle in the non-injected area of the corpus.

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