Journals of Gerontology Series A: Biological Sciences and Medical Sciences, Vol 53, Issue 2 M87-M91, Copyright © 1998 by The Gerontological Society of America
The effect of adenosine on the reduced heart rate response to exercise in the elderly
EA Andros and JG Gerber
Division of Clinical Pharmacology and Toxicology, University of Colorado Health Sciences Center, Denver, USA.
BACKGROUND: In a previous study we demonstrated that excessive endogenous
adenosine production and/or response was responsible for the blunted
tachycardia to bolus intravenous doses of isoproterenol in the elderly. In
this study, we tested the hypothesis that excessive endogenous adenosine
may also be responsible for the diminished maximal tachycardia with aging.
METHODS: Twelve young (mean age 27.3 +/- .61 yr) and 12 older (mean age
66.8 +/- .9 yr) healthy men were asked to perform maximum exercise tests in
the presence of placebo or theophylline at plasma concentrations between
15-20 micrograms/ml. Heart rate, oxygen consumption, and respiratory gas
exchange ratio were continuously monitored and recorded during the
exercise. In addition, plasma lactate, glycerol, renin activity, and
catecholamines were measured before and after maximal exercise. RESULTS:
Maximum heart rate to exercise was higher in the young (190 +/- 3 bpm in
the young, 157 +/- 2 bpm in the old) and increased by 4.5 +/- 1.2 bpm in
the young and 9.8 +/- 2.6 bpm in the old with the administration of
theophylline that resulted in an equivalent serum concentration in the two
age groups. This age difference in the increase was not significant but
approached significance at a p value of .07. Maximum VO2 was also greater
in the young group and this was unaffected in both groups by theophylline
administration. The increase in serum lactate and plasma renin activity
(PRA) to exercise was higher in the young group both in the presence and
absence of theophylline. CONCLUSIONS: Our data could not identify excessive
adenosine in the older group as the cause of diminished maximal exercise
heart rate with aging. It is likely that the diminished chronotropic
response to exercise in the older humans is due to a mechanism intrinsic to
the cardiac excitatory tissue.
