Aging in rats is associated with an increase in adrenal apolipoprotein E

Extrahepatic tissues including the adrenal cortex are capable of synthesizing apolipoprotein E (apoE). Locally synthesized apoE is believed to affect cellular uptake, transport and redistribution of cholesterol within that organ. We and another laboratory have previously reported that the adrenal cortex of aged rats has an elevated cholesteryl ester content. The aim of this work was to investigate whether this elevation is accompanied by increased adrenal apoE levels in aged rats. A Western blotting technique with polyclonal goat anti-human-apoE antiserum was employed as a probe for studies. The results showed that: (a) anti-human-apoE antiserum not only detected apoE in human plasma and adrenal homogenate, but also cross-reacted with a protein (or proteins) resembling apoE in rat plasma and adrenal homogenate (or supernatant) with a molecular weight of 34,000-36,000; (b) rat adrenal apoE concentration (per unit weight of protein) increased with age; (c) the increase did not result from blood trapped in the gland, because after organ perfusion the adrenal of aged rats persistently exhibited 58% more apoE than that of young animals. In conclusion, rat adrenal apoE concentration appears to increase with age. Whether this increase mechanistically causes the accumulation of cholesteryl esters in the aged rat adrenal remains to be investigated.