Journals of Gerontology Series A: Biological Sciences and Medical Sciences, Vol 50, Issue 4 B213-B217, Copyright © 1995 by The Gerontological Society of America
Beta-adrenergic receptor downregulation and recovery in heart and lung in the Fischer 344 rat: effects of aging and correlation with mRNA levels
MH Raitt, C Tamblyn, JM Allen and IB Abrass
Division of Cardiology, University of Washington, Seattle, USA.
Using indirect methods to downregulate beta-adrenergic receptor (BAR)
density, several investigators have observed an aging-related delay in the
recovery of BAR density after downregulation and suggested this finding may
in part explain the decreased beta-adrenergic responsiveness associated
with aging. We downregulated BAR density in male Fischer 344 rats ages 3,
12, and 24 months using the direct BAR agonist, metaproterenol. Lung and
heart BAR density and BAR mRNA levels were measured daily for 5 days during
recovery. Heart BAR density was downregulated significantly more in the
24-month compared to the 3- month-old animals (ANOVA p < .05). The rate
of recovery of heart BAR density was greater in the 24-month compared to
the 3-month-old animals (ANOVA, p = .05). Lung BAR density showed no
significant age-related differences at baseline, after downregulation, or
during recovery. There was no significant change in lung or heart BAR mRNA
levels observed in association with downregulation of BAR density. The
previously documented decrease in myocardial beta-adrenergic responsiveness
with aging in this animal appears to not be related to delayed or
incomplete recovery of BAR density after agonist-induced downregulation,
but may be associated with greater initial downregulation of heart BAR
density.
