Influence of sympathetic tone on the reactivity to indorenate in the external carotid vascular bed of the dog.

The present study was designed to analyze the effects of drugs that interfere with sympathetic transmission on the external carotid vasodilator response induced by the 5-HT1A receptor agonist, indorenate, in pentobarbital-anesthetized dogs. Intracarotid (i.c.) infusions of indorenate (1000 micrograms/l min) produced an increase in external carotid blood flow (external C.B.F.) without modifying mean arterial blood pressure or heart rate. This effect of indorenate was dose-dependently antagonized by intravenous (i.v.) administration of the alpha 1-adrenoceptor antagonist, prazosin (1, 3.1, 10, 31 and 100 micrograms/kg), the ganglionic blocking agent, mecamylamine (0.031, 0.1, 0.31, 1, 3.1 and 10 mg/kg) or the 5-HT2 receptor and alpha 1-adrenoceptor antagonist, ketanserin (10, 31 and 100 micrograms/kg). It is concluded that indorenate-induced increase in canine external C.B.F. is dependent on the vascular neurogenic tone.