Growth and differentiation of the prostate gland depends upon androgens, yet overgrowth of the human prostate occurs later in life when serum levels of testosterone are declining. We have reported a similar phenomenon in the Brown Norway rat, but the age-dependent overgrowth of the prostate is confined to the dorsal and lateral lobes and, hence, is lobe specific. Because tissue growth depends upon the balance between proliferation and death of cells, the present study was designed to investigate whether cell death differed in the various prostatic lobes of Brown Norway rats as a function of age. Apoptosis of cells in the ventral, dorsal, lateral, and anterior lobes of the prostate was examined in young (4-month-old) and old (24-month-old) Brown Norway rats after castration. Whereas castration caused tissue weights of all four prostatic lobes to decrease over the course of 10 days, this occurred more rapidly and to a greater magnitude in the ventral than in the dorsal, lateral, and anterior lobes. Tissue DNA content, a measure of cell number, decreased only in the ventral lobe after castration. DNA fragmentation, indicative of apoptotic cell death, was detected by in situ labeling using the terminal deoxynucleotidyltransferase-mediated dUTP nick end-labeling method and as intranucleosomal cleavage of genomic DNA analyzed by agarose gel electrophoresis. Both methods demonstrated the correlation between loss of DNA content and apoptotic cell death in the ventral lobe, whereas only the highly sensitive terminal deoxynucleotidyltransferase-mediated dUTP nick end-labeling (TUNEL) method revealed relatively few dying cells in the dorsal, lateral, and anterior lobes after castration. Moreover, when examined as a function of age, less cell death occurred in all four lobes of old rats compared with young rats. In both young and old rat prostates, cell death was observed in epithelial and stromal cells within the ventral lobe where apoptotic cells were detected throughout the branched ductal network and were not restricted to a particular region. Taken together, these studies demonstrate the marked differences in cell death and survival between the different rat prostatic lobes in response to castration and further suggest that the androgen-sensitive apoptotic response is age dependent. Hence, the lower rates of cell death observed for the dorsal and lateral lobes, accompanied by the further decline that occurs with increasing age, are important components of the age-dependent and lobe-specific overgrowth observed for these lobes. Moreover, the age-dependent decline in apoptotic cell death observed in the prostates of old rats suggests that prostatic cells develop androgen independence as a function of age, and survival of these cells does not require androgen.
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