Effect of aging on rat skeletal muscle [beta]-adrenergic receptor
function male fischer 344 x brown norway rats.
Larkin, Lisa M., Jeffrey B. Halter, and Mark A. Supiano.
Divisions of Geriatric Medicine, Department of Internal Medicine,
and Institute of Gerontology, University of Michigan, and Geriatric
Research, Education, and Clinical Center, Department of Veterans
Affairs Medical Center, Ann Arbor, Michigan, 48109
APStracts 2:0239R, 1995.
In this study we tested the hypothesis that, in the male F344xBN rat,
aging would be associated with an increase in sympathetic nervous
system activity and a decrease in skeletal muscle [beta]-adrenergic
receptor ([beta]-AR) density and function. Radioligand binding
studies using 125I-iodocyanopindolol were done to evaluate [beta]-AR
density (Bmax) and antagonist binding affinity (Kd) in gastrocnemius
(GAS) and cardiac muscle from 6, 18, and 28-mo-old male F344xBN rats.
[beta]-AR function was measured as adenylyl cyclase (AC) activity
stimulated by the [beta]-AR agonist isoproterenol (ISP, 10-4M). Basal
arterial plasma norepinephrine (pNE) concentrations were higher in
the 28- compared to the 6- and 18-mo-old rats. Bmax was greatest and
ISP stimulated AC activity was unchanged in GAS muscle of the 28-
compared to the 6- and 18-mo-old age groups. In contrast, there was
an age-associated decrease in Bmax and ISP-stimulated AC activity in
cardiac muscle. In conclusion, there was an age-associated increase
in pNE concentrations in male F344xBN rats suggesting an increase in
sympathetic nervous system activity. In addition, there was an age
-associated increase in skeletal muscle [beta]-AR density, while in
skeletal muscle [beta]-AR stimulated AC activity remained unchanged
with age.
Received 31 March 1995; accepted in final form 14 August 1995.
APS Manuscript Number R215-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 15 September 1995.