Antierectile Role of the Sympathetic Nervous System in Rats

The effects of the pharmacological changes of sympathetic innervation were studied in a rat model of electrically induced erection. Stimulation of the cavernous nerve elicited an erectile response measured by intracavernous pressure and separated into latency phase, tumescence (corresponding to corpora cavernosa filling), full erection (ICPE: intravenous pressure during full erection) and detumescence (corpora cavernosa emptying). A close dependence of the corpora cavernosa filling rate, ICPE and corpora cavernosa emptying rate on arterial blood pressure was demonstrated. Ganglionic blockade by mecamylamine decreased ICPE. Chemical sympathectomy by 6-hydroxydopamine improved the entire erectile response. Phentolamine (alpha-adrenoreceptor blocking agent) and propranolol (beta-adrenoreceptor blocking agent) increased the latency phase. Phentolamine increased the corpora cavernosa filling rate and the ICPE, while propranolol decreased them. These results demonstrate that a sympathetic inhibition decreases the erectile response to stimulation and that this inhibition is due not only to norepinephrine, but possibly to a nonadrenergic noncholinergic transmitter, colocalized with norepinephrine.