Alpha-adrenoceptor-mediated penile erection in dogs: in vivo and in vitro observations

We have evaluated the role of adrenergic components in the pelvic splanchnic nerve on the erectile function in the dog. Electrical stimulation of pelvic splanchnic nerves increased blood flow in the internal pudendal artery and also elevated the cavernous pressure. These increases were blocked in part by phentolamine or methylene blue, but not by propranolol or atropine. The effects of cholinergic and adrenergic agonists and antagonists on mechanical responses were also examined in muscle strips obtained from various arteries in the intrapelvic region including the internal pudendal artery. Norepinephrine induced contraction in the iliac artery and relaxation in the internal pudendal artery, and both the contraction and relaxation responses were blocked by phentolamine but not by propranolol. These findings suggest that in the dog, alpha-adrenergic components projected through the pelvic splanchnic nerve may contribute to penile erection, together with cyclic GMP-mediated mechanisms.