title: Enhanced sympathetic mediation of chronotropic baroreflexes in old Sprague-Dawley rats.
abstract: We compared reflex heart rate responses elicited during intravenous infusions of phenylephrine or sodium nitroprusside in conscious 4- and 24-month-old male Sprague-Dawley rats to determine whether baroreflex regulation changes with age. Underlying neural mechanisms were assessed by repeating baroreflex tests following cholinergic blockade with methylatropine or beta-adrenergic blockade with propranolol. Basal blood pressures always tended to be higher, while corresponding heart rates were lower, in old than in young rats. Reflex bradycardia (but not tachycardia) was initially weaker in 24-month-old rats as were reductions in both reflex bradycardia and tachycardia after cholinergic blockade. On the other hand, the reduction in reflex tachycardia following beta-adrenergic blockade in old rats was more pronounced and almost equal to that produced by combined cholinergic and beta-adrenergic blockade. From these results we conclude that with old age in male Sprague-Dawley rats, just as has been shown previously in Fischer 344 rats, predominant efferent pathways for regulating heart rate reflexes are also altered to become almost exclusively beta-adrenergic or sympathetic.
authors.affiliation: Department of Pharmacology, College of Health Sciences and Hospital, University of Kansas Medical Center, Kansas City 66103.
authors.forename: R D
authors.initials: RD
authors.lastname: Buñag
authors.forename: T L
authors.initials: TL
authors.lastname: Teräväinen
authors.forename: L
authors.initials: L
authors.lastname: Eriksson
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D001286:Atropine Derivatives / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D004525:Efferent Pathways / Q000502:physiology; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D008297:Male; D009599:Nitroprusside / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011311:Pressoreceptors / Q000187:drug effects / Q000502:physiology*; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012018:Reflex / Q000187:drug effects / Q000502:physiology; D013564:Sympathetic Nervous System / Q000502:physiology
chemical_list: D001286:Atropine Derivatives; D009599:Nitroprusside; D010656:Phenylephrine; C006649:methylatropine; D011433:Propranolol