Abstract

Evidence is presented that Su-4029 has no effect or only a transient suppressant effect in efferent sympathetic pathways during the first few hours following its administration to dogs and cats. In cats pretreated intravenously with 10 mg/kg of Su-4029, the response of the splanchnic vasculature to stimulation of the greater splanchnic nerve was diminished; the vasoconstriction evoked in the hindlimb by stimulation of the lumbar sympathetic chain was not invariably reduced ; the nictitating membranes were not relaxed nor were there reductions in the responses of the membranes to stimulation of their sympathetic supplies and to injected norepinephrine. Pretreatment of cats with 10 mg/kg of Su-4029 depleted hearts of catecholamines, but did not affect the catecholamine contents of aortas or smooth muscles of the nictitating membranes. In dogs pretreated with 30 mg/kg of Su-4029, stimulation of the sympathetic supply to the limb resulted in vasodihation which could be blocked with atropine; nictitating membranes were not relaxed; hearts and aortas were depleted of their catecholamine contents. Su-4029 did not produce gross alterations in the electrical activity recorded from the carotid sinus nerve of cats; in pretreated cats the electrical activity in the greater splanchnic nerve appeared to be reduced. The significance of these findings is discussed.