Cardiovascular Reactivity in the Dog after Chemical Sympathectomy with 6-Hydroxy dopamine

Abstract

The cardiovascular responses to intravenous injections of noradrenaline, isoproterenol, and phenylephrine were studied in unanesthetized and anesthetized dogs before and after chemical sympathectomy with 6-hydroxydopamine (6-OH-DA), 50 mg/kg. Three days after 6-OH-DA pretreatment, the blood pressure response to noradrenaline in unanesthetized dogs was increased significantly despite the presence of a marked reflex slowing of the heart. Chronotropic and pressor responses to noradrenaline were likewise increased in anesthetized and vagotomized dogs after 6-OH-DA pretreatment. Not only was the amplitude of the responses to noradrenaline increased after 6-OH-DA pretreatment but their duration was likewise prolonged. In contrast, the cardiovascular responses to isoproterenol and phenylephrine did not appear significantly changed in 6-OH-DA pretreated dogs. These results are consistent with the development of a presynaptic type of supersensitivity in dogs pretreated with 6-OH-DA.