Dogs and chimpanzees are the only experimental animal species that develop BPH spontaneously. In both species the BPH occurs in an age-dependent manner, but there are important differences from the human BPH.
Nonhuman primates represent the best model for most human diseases when it comes to similarity to human pathology. BPH is not an exception. Chimpanzee prostate is anatomically very similar to the human prostate (Steiner et al., 1999). It is divided into two lobes— caudal, which resembles the human transition and peripheral zone, and cranial, which resembles the central zone in the human prostate. The age dependence of BPH in chimpanzees does not differ from human BPH, and histological evaluation has shown that the epithelium/ stroma ratio is also similar. Is chimpanzee BPH an ideal model? No, but it is currently the best available. The problems lie just in the availability, as primates are available for research use only in specialized primate research centers. Spontaneous BPH occurs in chimpanzees at their elderly age—cca 30 years. Furthermore, the prostate-specific antigen is present only in very low concentration; thus, to follow the development of BPH in primates biochemically is complicated. On the other hand, the presence of outlet obstruction enables functional evaluation.
Canine prostate lacks a capsule, and its growth is oriented not to the urethra, but to the pelvic cavity due to anatomical relations, including the lack of a fixation to symphysis. This explains why BPH in dogs does not result in LUTS but is mostly asymptomatic or it causes defecation problems due to rectal obstruction. Canine prostate is not divided into clear morphological subunits; similarly, canine BPH does not resemble the nodular pathogenesis of human BPH. Moreover, the histological picture of canine BPH involves epithelial proliferation in contrast to human BPH, where fibrostromal proliferation is usually present. This might be explained by the finding that the activity of 5-alpha reductase is higher in the epithelium than in the stroma. Several other biochemical differences have been described, including the expression of prostate-specific antigen and prostate-specific esterase. Nevertheless, canine spontaneous BPH is a widely used model of human BPH, and if differences are taken into account, pathophysiologic and therapeutic studies can make use of this model.
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