Differential anesthetic depression of chronotropic baroreflexes in rats.
To assess anesthetic alteration of chronotropic baroreflexes, arterial pressure and heart rate (HR) were monitored continuously during intravenous (i.v.) infusions of phenylephrine or sodium nitroprusside in rats that were either awake or anesthetized (with pentobarbital, urethane, or chloralose). Ensuing reflex HR responses during each drug infusion were determined in two ways: (a) at 10-s intervals (time analysis), and (b) with every 5-mm Hg change in pressure (pressure analysis). Results were less variable with pressure than with time analysis. With responses from awake rats as a basis for comparison, pressure analysis showed that pentobarbital greatly attenuated both reflex tachycardia and bradycardia, whereas urethane and chloralose reduced only reflex tachycardia. Depression by pentobarbital of both reflex tachycardia and bradycardia suggests severe attenuation of both sympathetic and parasympathetic tone. In contrast, preferential alteration of reflex tachycardia by chloralose and urethane implies a greater attenuation of sympathetic than parasympathetic tone.
Department of Pharmacology, College of Health Sciences, and Hospital University of Kansas Medical Center, Kansas City 66103.
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Barringer
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Buñag
D000758:Anesthesia; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D006339:Heart Rate / Q000187:drug effects*; D008297:Male; D011311:Pressoreceptors / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D012018:Reflex / Q000187:drug effects