Changes in penile volume during some cardiovascular reflexes and reactions in rabbit

The effect of various cardiovascular reflexes and reactions on the plethysmographically recorded penile volume in rabbit was investigated. Stimulation of the aortic nerve or direct stimulation of the carotid sinus produced increase in penile volume, while carotid occlusion produced decrease. Brief volume load or protoveratrine given into the right atrium produced increase in penile volume. Asphyxia, hypercapnia, hypoxia, cyanide and lobeline produced decrease in penile volume, while hypocapnia increased it. Moderate blood taps decreased penile volume, while hypocapnia increased it. Moderate blood taps decreased penile volume. With the exception of the response to asphyxia all these reactions required intact vasomotor nerves. Clonidine increased penile volume if vasomotor nerves were intact but decreased it if the penis was decentralized. Penile volume decreased in shivering animals but increased on warming. Carotid occlusion impaired erectile responses to hypogastric and pelvic nerve stimulation. In certain experiments this effect was more pronounced in the latter case. It is concluded that the medullary neuron pool responsible for penile vasomotor tone participates in general reflex cardiovascular homeostasis and that this may have implications for normal erectile responses.