Benztropine-induced prolongation of responses to vasodilator nerve stimulation in the canine paw pad.

After blockade of noradrenergic transmission with guanethidine in anaesthetized dogs, stimulation of the peripheral end of the cut tibial nerve (1 Hz, 10 pulses) produces a vasodilator response which is localized to the circulation of the paw pads. The time course of the response is considerably prolonged after systemic administration of the dopamine-uptake blocking drug, benztropine (1 mg/kg). This effect is not due to inhibition of Uptake 1, as benztropine, unlike desmethylimipramine, does not prolong responses to noradrenergic vasoconstrictor nerve stimulation. The results support previous evidence suggesting that the dilator response to tibial nerve stimulation involves neural release of dopamine.