Androgen receptor messenger ribonucleic acid (mRNA) in the rat liver: Changes in mRNA levels during maturation, aging, and calorie restriction

By means of RNAase protection assay with an antisense cRNA probe, we have shown that the liver of the young adult male rat contains androgen receptor (AR) mRNA to a level of 4% compared to the prostate. Steady state levels of AR mRNA in the liver show both sex and age specificity. Compared to that of the male, the female liver contains a markedly reduced amount of AR mRNA. AR mRNA is almost undetectable in livers of prepubertal male (<35 days old) and senescent male (>750 days old) rats. Both prepubertal and senescent animals are relatively insensitive to the androgenic induction of α_2u-globulin, a hepatic secretory protein. The age-dependent decline in hepatic androgen sensitivity and AR mRNA level can be delayed considerably by a 40% reduction in the dietary calorie intake. Analysis of poly(A)-containing RNA from two liver cell populations, hepatocytes and nonhepatocytes, revealed that only the hepatocytes that express α_2u-globulin gene contain AR mRNA. From these results and our earlier observation of in vitro induction of α_2u-globulin in isolated rat liver, we conclude 1) that androgen can act directly on hepatocytes to promote α_2u-globulin synthesis; 2) that changes in the hepatic androgen sensitivity during maturation and aging are reflections of the age-dependent expression of the receptor gene; and 3) that retardation of the age-dependent loss of androgen sensitivity by calorie restriction is due to a concomitant delay in the decline of the hepatic AR mRNA level.