Age-related changes in guinea pig prostatic stroma

The histology of benign disease of the human prostate (benign prostatic hyperplasia) is heterogeneous. No other species demonstrates the same complexity, and current animal models do not appear to fully encompass the stromal and epithelial developmental changes involved in the human disease. This study describes age-related changes in the prostatic smooth muscle stroma of guinea pigs and humans, which may be pertinent to some aspects of the disease process in humans.

Histologic and ultrastructural changes were examined and measured in the prostates of guinea pigs during aging (2 weeks to 31 months). Similar measurements were also made in human prostatic tissues during aging and the development of benign prostatic pathology.

Morphometric analyses of prostates in guinea pigs and men demonstrated similar changes in stromal volume with age. The stromal volume proportion of the prostate in both species decreases at puberty due to the expansion of the epithelial cell compartment, and is followed by a progressive increase during adulthood until a maximum stromal content of approximately 75% of total tissue volume is reached at age 2 years in guinea pigs, and at age 70 years in men. The pathognomic feature of nodularity and the dramatic increase in gland size observed during the late stages of human benign prostatic disease did not occur in the guinea pig prostate. Ultrastructural analysis of guinea pig prostatic smooth muscle cells identified a progressive hypertrophy (approximately 10-fold) from prepuberty through to old age. Two-thirds of smooth muscle cells in the prostatic stroma of aging individuals of both species demonstrated perinuclear organelles (rough endoplasmic reticulum and free ribosomes) that were not present in younger individuals.

The prominent histologic features of the guinea pig prostate during aging are increased stromal mass, significant stromal fibrosis, and occasional prostatitis. These features are frequently observed in men with clinical benign prostatic hyperplasia. The age-related increases in prostatic smooth muscle cell size and content of perinuclear organelles in the guinea pig suggest a re-activation of cellular synthetic activity. The similarity in some features of the prostatic smooth muscle stroma between aging men and guinea pigs suggests that there may be common pathophysiologic processes. We conclude that the guinea pig could be a useful model for examination of the age-related hypertrophy of the smooth muscle cell and the processes inducing reversion to a more synthetic smooth muscle cell phenotype.