Prolonged exercise alters beta-adrenergic responsiveness in healthy
sedentary man.
Eysmann, Susan B., Ernest Gervino, Dorothy E. Vatner, Sarah E. Katz,
Lisa Decker, Pamela S. Douglas.
Charles A. Dana Research Institute and the Harvard-Thorndike
Laboratory of the Department of Medicine, Beth Israel Hospital,
Boston, MA., Harvard Medical School and the New England Regional
Primate Research Center, Southborough, MA
APStracts 2:0483A, 1995.
To examine whether beta adrenergic desensitization occurs after
prolonged exercise, echocardiograms, heart rate responses to
isoproterenol, plasma catecholamines and circulating lymphocyte beta
adrenergic receptors were examined in ten sedentary normal subjects
at rest and after brief (10 min) and exhaustive (mean duration 95
min) cycle exercise. Resting end-diastolic volume and ejection
fraction were significantly reduced after exercise (from 120+/-34 to
100+/-26 ml and from 60+/-0.4 to 54+/-0.6 %, both p<0.05). The
amount of isoproterenol needed to increase heart rate 15 and 25 bpm
increased in a dose (exercise duration) related fashion and the
increase in amount of isoproterenol needed after prolonged exercise
was closely related to the decrease in ejection fraction, r2=.67,
p=0.004. Circulating lymphocyte beta receptor density and affinity,
agonist binding and adenylyl cyclase levels were unchanged with
prolonged exercise. In conclusion, prolonged exercise in sedentary
normal subjects resulted in reduced cardiac chronotropic
responsiveness to isoproterenol which was not reflected in peripheral
lymphocyte beta adrenergic receptor down regulation.
Received 12 April 1995; accepted in final form 2 October 1995.
APS Manuscript Number A403-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 November 95