AGE-DEPENDENT AND LOBE-SPECIFIC SPONTANEOUS HYPERPLASIA IN THE BROWN-NORWAY RAT PROSTATE

We showed previously that exogenously administered testosterone caused age- and lobe-specific overgrowth of the prostate in Brown Norway rat s. A common feature observed in testosterone-treated animals was cell hypertrophy in each of the ventral, dorsal, and lateral lobes of both young (6 mo old) and old (24 mo old) rats. By contrast, hyperplasia wa s seen only in the dorsal and lateral lobes of old rats treated with t estosterone. These observations prompted us to examine whether age- an d lobe-specific overgrowth might also occur in untreated rats as a con sequence of the endogenous hormonal milieu. To this end, blood and pro states were collected from a large number (25-30 rats per group) of 4- to 6-mo-old (young) and 21- to 24-mo-old (old) Brown Norway rats. Bot h serum testosterone (-45%) and estradiol (-22%) concentrations decrea sed significantly with age, but the greater magnitude of the decrement in testosterone relative to estradiol led to a reduction in the serum testosterone:estradiol ratio. Paradoxically, although the prostate is androgen dependent, the wet weight, protein, and DNA contents increas ed significantly with age in the dorsal and lateral lobes of old rats despite the decrease in testosterone level. Histologic examination rev ealed that the increased weights and DNA contents of the dorsal and la teral lobes in old rats coincided with an increased number of epitheli al cells in the distal and intermediate segments of these lobes, indic ative of hyperplasia but independent of change in cell size. Taken tog ether, these results Show a spontaneous age-related overgrowth of cell s in the dorsal and lateral prostatic lobes of old Brown Norway rats d espite diminished serum testosterone concentrations. The aging Brown N orway rat, therefore, may be a useful model for studies of some aspect s of the pathogenesis underlying spontaneous age-related prostatic hyp erplasia.