EFFECT OF AGING ON REGULATION OF SDI-1 IN RAT HEPATOCYTES

We examined basal and EGF stimulated DNA synthesis as well as sdi-1 mR NA and protein in primary hepatocyte cultures, and basal levels of sdi -1 mRNA and protein in whole liver homogenates from 6 and 24 month old rats. Since EGF stimulated DNA synthesis decreases with age, it was h ypothesized that basal and EGF stimulated levels of sdi-1 mRNA and pro tein, an inhibitor of DNA synthesis, might increase. Surprisingly, how ever, both sdi-1 mRNA and protein actually decreased both in cells and homogenates of old rats. These results indicate that the age-related impairment in EGF stimulated DNA synthesis in hepatocytes appears to o ccur prior to or parallel with sdi-1 expression and cannot be explaine d on the basis of increased inhibition due to elevated levels of this protein. (C) 1996 Academic Press, Inc.