title: Effects of fitness and age on the response to vagotonic atropine.
abstract: Previous work indicates compromised cardiac vagal control plays a prominent role in reducing arterial baroreflex gain with age, however older fit individuals display cardiovagal baroreflex responses similar to young individuals. The purpose of this study was to test the hypothesis that chronic aerobic exercise mitigates against age-related declines in cardiac parasympathetic receptor function. In forty-four young and old (fit and unfit) individuals, we used the parasympathomimetic responses to low doses of atropine to probe cardiac cholinergic receptor responses. Data were collected before and after eight doses of atropine sulfate from 0.4 to 7.2 microg/kg. Chronotropic responses were assessed from average RR intervals and heart rate variabilities were derived in time and frequency domains. All subjects exhibited bradycardia with at least one dose of atropine and peak bradycardia occurred at a similar dose in each group. However, changes in heart rate variability did not consistently track the chronotropic responses within subjects (r-square from 0.90 down to 0). As expected, basal RR interval was longer in the fit groups and was unaffected by age. However, the degree of RR interval lengthening with parasympathomimetic atropine was unaffected by physical fitness and was significantly less in all older subjects. These data indicate there are certain prepotent age-related declines in the cardiac parasympathetic system that cannot be prevented by regular physical activity.
authors.affiliation: Cardiovascular Research Laboratory, Department of Physical Medicine & Rehabilitation, Spaulding Rehabilitation Hospital, Boston, MA 02114, USA.
authors.forename: Kichang
authors.initials: K
authors.lastname: Lee
authors.forename: Glen
authors.initials: G
authors.lastname: Picard
authors.forename: Stacy D
authors.initials: SD
authors.lastname: Beske
authors.forename: Gyu-Sam
authors.initials: GS
authors.lastname: Hwang
authors.forename: J Andrew
authors.initials: JA
authors.lastname: Taylor
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000187:drug effects* / Q000502:physiology; D000704:Analysis of Variance; D001146:Arrhythmia, Sinus / Q000139:chemically induced; D001285:Atropine / Q000494:pharmacology*; D001794:Blood Pressure / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D005260:Female; D005583:Fourier Analysis; D006339:Heart Rate / Q000187:drug effects; D006801:Humans; D008297:Male; D008875:Middle Aged; D010276:Parasympatholytics / Q000494:pharmacology*; D010809:Physical Fitness / Q000502:physiology*; D014630:Vagus Nerve / Q000187:drug effects* / Q000502:physiology
chemical_list: D010276:Parasympatholytics; D001285:Atropine