Journals of Gerontology Series A: Biological Sciences and Medical Sciences, Vol 54, Issue 9 B384-B392, Copyright © 1999 by The Gerontological Society of America
Dietary restriction alters retinol and retinol-binding protein metabolism in aging rats
S Chevalier, WS Blaner, V Azais-Braesco and B Tuchweber
Department of Nutrition, University of Montreal, Quebec, Canada.
Recent studies reported that retinoid metabolism was influenced by long-
term dietary restriction (DR) in rats. Because plasma retinol was decreased
in rats subjected to DR, it was thought that this dietary manipulation may
have an effect on retinol-binding protein (RBP) metabolism. Thus, the aim
of this study was to assess retinoids, RBP, and transthyretin (TTR) levels
in plasma and liver of young (3 months), adult (12 months), and old (22
months) female Sprague-Dawley rats fed ad libitum (AL) or subjected to a
40% DR, enriched (DR+), or not (DR), with vitamins and minerals. Results
indicate that hepatic total retinoid concentrations and content increased
with age in all the groups. DR+ rats showed higher hepatic retinoid
concentrations than age- matched AL and DR rats. Adult and old DR and DR+
rats exhibited significantly lower plasma RBP-retinol and higher total
retinoic acid levels than corresponding controls, although these parameters
were not influenced by aging. Liver RBP levels were also decreased in DR
and DR+ rats when compared to respective AL controls. There was a slight
age- related decline in plasma TTR levels in DR and DR+ rats which was not
associated with modifications in liver TTR levels. Hepatic gene expression
of RBP and TTR, as evaluated by Northern blot hybridization, did not change
with age or diet, suggesting that the lower levels of plasma RBP-retinol
and liver RBP in vitamin A-sufficient rats subjected to DR may reflect
post-transcriptional alterations and/or accelerated degradation of hepatic
RBP. The elevated plasma levels of retinoic acid may represent an adaptive
mechanism developed by DR rats to maintain retinoid-dependent functions.
