ABSTRACT
Human benign prostatic hyperplasia is a predominantly stromal hyperplasia with accumulation of connective tissue. The main ultrastructural finding, which may be causal, is an activation of the smooth muscle cells, as seen by an increase of the volume density of the organelles within these cells. The dog is widely used as an animal model for human prostatic hyperplasia in spite of several differences. In this work the smooth muscle cells of the spontaneous and steroid-induced (by treating castrates with dihydrotestosterone and estradiol) prostatic hyperplasia of dogs were analysed by electron microscopical morphometry, and compared to estrogen or tamoxifen (antiestrogen) treated dogs as well as to untreated or castrated control dogs. The results clearly show that the prostatic smooth muscle cells of the dog can be activated by estrogen as well as tamoxifen, which proves the estrogenic side activity of the latter. In marked contrast to that, neither in the spontaneous nor in the steroid-induced prostatic hyperplasia could an activation of the smooth muscle cells be found. This is a most important difference from human benign prostatic hyperplasia, which limits the use of this animal model, and it might even be the explanation of the different reaction of human and canine prostatic hyperplasia to therapeutic hormonal manipulations.