Reduced Cardiovascular Responsiveness to Hypothalamic Stimulation during Urethane and Amobarbital Anesthesia

Abstract

Graded pressor responses to electrical stimulation of the posterior hypothalamus were accompanied by variable changes in heart rate. Tachycardia caused by weak currents was prevented by propranolol while reflex bradycardia associated with pressor responses to strong currents was abolished by atropine. Rats anesthetized with urethane were generally more responsive to hypo thalamic stimulation than those anesthetized with amobarbital. Stimulation thresholds were significantly lower when rats were awake than when they were anesthetized with either anesthetic. In some experiments, responses that were initially depressor during amobarbital anesthesia, later became pressor when the rats were awake or anesthetized with urethane. Our findings indicate that general anesthesia alters cardiovascular responsiveness to hypothalamic stimulation qualitatively as well as quantitatively.