Aging in the AXC/SSh rat: diminished prostate L-ornithine decarboxylase (ODC) activity reflects diminished prostate...

Immunotitration of L-ornithine decarboxylase (ODC) activity in ventral prostates of young mature (6-month-old) and aged (26-month-old) AXC/SSh rats established that the relation between enzyme activity and prostate ODC mass content was age invariant, demonstrating that the 4-fold diminution in prostate ODC activity in aged subjects represents decreased ODC protein content. Testosterone treatment of aged rats increased prostate ODC activity 2-fold and did not affect prostate ODC half-life. These latter findings and the preceding observation established that the testosterone-mediated increase in prostate ODC activity in aged individuals reflected increased ODC mass content. The half-life of prostate S-adenosyl-L-methionine decarboxylase, another prominent enzyme of polyamine biosynthesis, also was not altered by testosterone treatment of 26-month-old animals. The age-related diminution and testosterone-mediated increase in ventral prostate ODC activity occurred in concert with comparable quantitative changes in ventral prostate ODC transcript content. Because plasma testosterone content was age invariant between 3 and 18 months, the age span during which much of the reduction in prostate ODC activity occurs, and then declined by 50% at 26 months, our studies suggest that age-related diminutions in prostate ODC activity and transcript content reflect altered prostate sensitivity to androgen rather than response to diminished plasma testosterone content. Our data imply that age-related alterations in androgen regulation of androgen-responsive genes may be characteristic of the prostate during aging.